Cross-linked glucose isomerase.

Cross-linked, water-insoluble glucose isomerase and method for its preparation

The invention relates to a new type of water-insoluble glucose isomerase formed by a cross-linked solidified crystalline enzyme. The invention also relates to a process for the preparation of cross-linked crystalline glucose isomerase.

The use of solid support-bound or immobilized enzymes in continuous reactors is becoming the predominant technology, as this allows for savings in enzyme costs and product purification. An example of such a process is the conversion of glucose to fructose by immobilized glucose isomerase.

Because enzymes are generally water-soluble, a special enzyme immobilization technique must be used in the continuous process: the enzyme must be bound to the solid phase in one way or another so that it is insoluble in water, but must not be inactivated. Several techniques have been developed: absorption into the carrier, covalent bonding to the carrier, crosslinking to the carrier, and microencapsulation; also the whole enzyme-producing microbe is bound to the solid phase. A good summary of the 25 techniques used can be found, for example, in Moo-Young, M. (ed), Comprehensive Biotechnology, Vol 2, Pergamon Press, London 1985, pp. 191-211.

In known methods, the enzyme is bound to a separately prepared carrier material, which in itself may be advantageous in terms of chemical kinetics or substrate flow technology. Unfortunately, in most cases, the support material is very expensive and can even cost many times the cost of the enzyme acting as a catalyst itself, especially in the case of large-scale mass production, such as in the sugar industry. Alternatively, the enzyme is immobilized by cross-linking with an inert massive component, for example gelatin. In any case, the prior art enzyme itself constitutes a fraction, usually less than 5%, usually 1-2%, by weight and volume of the material used in the process.

Cross-linking with glutaraldehyde has been a technically very important method e.g. upon immobilization of glucose isomerase; as is known, glutaraldehyde is permitted for use in the immobilization of enzymes used in food processes.

Other technically used methods are binding to ion exchangers or absorption on a solid support. An example of such an application is in U.S. Patent 4,699,882 (K. Visuri; Stabilized glucose isomerase); however, the support used in this known process is relatively expensive, and in addition, the process requires a large reactor.

The use of bulky carrier materials and large-sized devices has a wide range of cost implications that are not necessarily due to the enzyme itself used at all; such are:

- construction costs for process equipment and factory premises,

- the cost of acquiring (re-acquiring) the carrier material,

- the cost of disposing of the inactivated enzyme material,

- labor costs for emptying and filling reactors (or regenerating the carrier),

- secondary costs due to reactor slowness; thus, long residence times often result in non-enzymatic adverse side reactions, especially in the production of fructose.

There are several examples in the scientific literature of cross-linking of crystalline enzymes with glutaraldehyde. Quiocho and Richards (Proc.Natl.Acad.Sci (US) 52 (1964) p. 833 and Biochemistry 5 (1966) p. 4062) were the first to use glutaraldehyde to cross-link carboxypeptidases. Bishop and Richards (J. Mol. Biol. 33 (1968) pp. 415-421) have crosslinked crystalline beta-lactoglobulin with a 1% aqueous solution of glutaraldehyde at room temperature. Crystals were used to study the electrical properties of the enzyme. Haas (Biophysic.Journ. 8 (1968) pp. 549-555) has crosslinked lysozyme crystals in the presence of 4% sodium nitrate solution (pH 8) using a glutaraldehyde content of 12%.

Dyer, Phillips, and Townsend (Thermochimica Acta 8 (1974) pp. 456-464) have studied the thermostability of crystalline carboxypeptidase cross-linked with glutaraldehyde. They noted that cross-linking led to an increase in stability. TUchsen and Ottesen (Carlsberg Res.commun. 42 (1977) pp. 407-420) have studied the kinetic properties of crystalline subtilisin cross-linked with glutaraldehyde in sodium sulfate solution. The activity of the crystals was high on low molecular weight substrates but low on high molecular weight substrates.

Wong et al. (Biochem. And Biophysic. Research Communications 80 (1978) pp. 886-890) have crosslinked a microbial acidic protease in ammonium sulfate solution with glutaraldehyde. In crosslinking, the presence of ammonium sulfate was considered a technical drawback.

Morozov and Morozova (Biopolymers 20 (1981) p. 451467) have crosslinked crystalline lysozyme, hemoglobin and myoglobin using 2-6% glutaraldehyde solutions and a reaction time of 2-10 days at room temperature. Lee et al. (Bioorganic Chemistry 14 (1986) p. 202210) have crosslinked crystals of alcohol dehydrogenase with glutaraldehyde in the presence of 2-methyl-2,4-pentanediol (25%).

In these works, enzyme crystals have been cross-linked to achieve the objectives of basic research. Often, enzyme teas are so weak in structure that they cannot withstand the beam used in X-ray diffraction studies, but they can often be stabilized for these purposes with glutaraldehyde. In addition, crystals have been cross-linked for research purposes on stability and catalysis kinetics. In cases where cross-linking of the crystals has been successful, only glutaraldehyde and the solution in which the enzyme remains crystalline have been used as the medium. All in all, the insoluble crystal is formed directly from the interaction between glutaraldehyde and the enzyme protein.

It is known that glutaraldehyde often has difficulty producing an insoluble enzyme, especially if the protein contains relatively little lysine. This problem is often circumvented by mixing with a known enzyme such as albumin, a protein which is known to be readily insoluble (GB Broun, Methods in Enzymology, 44 (1976) p. 263). Such addition of an inert foreign protein is, of course, out of the question when attempting to cross-link a crystalline enzyme. Previously, no means have been proposed that could be used when crosslinking of a crystal to insolubility with glutaraldehyde alone fails.

As mentioned above, immobilization of glucose isomerase with glutaraldehyde is known. In this case, the isomerase is cross-linked either directly to the producer microbe itself or, in addition, to gelatin, for example. Such processes are in full industrial use. In contrast, cross-linking of glucose isomerase crystals to an insoluble form has not been successful and no such enzyme has been used as a catalyst in the isomerization process.

It has now been found that it is possible to cross-link the crystals of glucose isomerase so that the original crystalline state is maintained and also the enzymatic activity of the enzyme remains very high, even the same as that of the original enzyme. The product according to the invention is insoluble in any of the solvents which are relevant to the technical use of the enzyme. The cross-linked crystalline enzyme can be used as such in a technical isomerization process as a packing for an isomerization column. With the new cross-linked crystalline enzyme, it is possible to carry out a continuous isomerization process in much smaller and more efficient columns.

According to the process of the invention, the crystals of glucose isomerase are crosslinked with a dialdehyde, such as glutaraldehyde, and a compound containing at least one amino group, such as an ammonium compound, an amine or an amino acid, preferably an ammonium salt or lysine. Several amines and amino acids are suitable for use. It is also apparent that in addition to glutaraldehyde, several other dialdehydes and amino group reactants known as crosslinking reagents are suitable for use in the process.

The activity of the solid crystalline enzyme prepared by the method of the invention is substantially the same as that of the free enzyme. The solid, crystalline enzyme can be used as such as a column packing in a continuous process. It is very stable and very resistant to mechanical stress.

If desired, the crosslinked crystals can be further bonded into larger pieces, spherical, plate-like or ribbon-like, or in another shape by chemical-physical means known per se. The enzyme products thus obtained withstand very different mechanical treatments.

The method according to the invention is described in more detail below.

Preparation of crystalline glucose isomerase used as raw material

Ammonium sulfate (about 10% by weight) is dissolved in a glucose isomerase solution (1-10% by weight of isomerase as determined as dry protein). Cool the solution slowly to about 0-2 ° C, stirring constantly. In this case, the isomerase crystallizes practically completely (more than 95%). Instead of ammonium sulfate, for example, magnesium sulfate or sodium sulfate can be used as the crystallizing agent. The content of the salts used can vary within wide limits, for example from 5 to 25% by weight. The time required for the crystallization process varies within wide limits, for example 1 hour to several days. For the preparation of large crystals, it is preferable to use slow cooling and the purest possible isomerase. Crystallization is described in U.S. Patent 4,699,882 (Visuri).

After crystallization, the crystalline mass is separated by sedimentation or centrifugation from its mother liquor. If necessary, wash the crystalline mass with clean solutions of ammonium sulphate, magnesium sulphate or other material suitable for crystallization. For cross-linking, a tightly sedimented or centrifuged crystalline mass is used which does not contain free excess mother liquor. The typical activity of such a crystalline mass is 10,000 Glu / g. It contains 20-30% by weight of pure enzyme protein, determined as dry matter. It should be noted that enzyme crystals lose their structure if dried.

cross-linking

The crystalline mass is slurried in a brine in which the crystals are insoluble. The concentration of enzyme crystals in the solution can vary widely, for example from 2 to 17% by weight, determined as dry matter.

Ammonium salt is added to the solution, unless the saline solution already contains ammonium, or a suitable amine or amino acid, for example lysine. The pH of the mixture is adjusted to between 5 and 9, preferably to 7-8, by adding, for example, sodium hydroxide solution. For the control of acidity, for example, a phosphate buffer, for example 0.05 m sodium phosphate, can be advantageously used. The useful concentration of added amine or amino acid varies over a wide range and is dependent on the concentration of other components. The product of the invention is prepared in good yield with amine or amino acid contents

1-15% of the final weight of the mixture.

Glutaraldehyde is then added to the mixture to initiate the crosslinking reaction. The dosage of glutaraldehyde can be varied within wide limits, from 1 to 45% by weight, based on the wet enzyme crystal mass. The most preferred dose depends, inter alia, on the concentration of amine in the mixture. In general, the preferred concentration is 3-4.5 g glutaraldehyde / 3 g isomerase calculated as dry enzyme. During the reaction, the mixture is stirred continuously; the temperature is 2-25 ° C. Low temperature is an advantage, but temperature does not seem to be very important. The reaction can take place quite rapidly, in a few minutes, especially at higher temperatures. At low temperatures, the reaction time may be 20 hours.

After the reaction, insoluble crystals are separated from the mixture by sedimentation or centrifugation. The crystalline mass is washed by slurrying in water or suitable brine and centrifuging again. The washing is repeated several times until the crystalline mass is pure enough to be used as a catalyst. In connection with washing, it is also advantageous to rinse off the fine precipitate.

The resulting crystalline mass should not be dried if it is to be used as a catalyst in an enzymatic process. The moist crystalline mass remains fully active for at least six months without special measures.

Characterization of the final product

The crosslinked crystals prepared according to the invention are similar in appearance and size to ai

52 85 original raw alnecrystals. The size of the crystals is not critical. Crystals with a diameter of 100-200 μm are particularly suitable for technical use.

The most important property of the crystals according to the invention is their insolubility in water, brine and sugar solutions. Of particular importance is that the isomerase crystals do not dissolve in concentrated solutions of glucose and fructose even at high temperatures. A temperature of 60 ° C and a sugar content of 45% by weight are generally used in industrial processes. The cross-linked crystals do not dissolve under such conditions, nor at any other sugar content, nor at higher temperatures (up to 100 ° C).

The activity of the cross-linked crystals is of the same order of magnitude as that of the original enzyme. It is technically significant and advantageous that their activity is many times that of an enzyme immobilized on an inert carrier.

By cross-linking the enzyme as a crystal, a particular additional advantage is achieved as a result of the fact that the forces inherent in the crystal itself that hold the crystal together significantly stabilize the enzyme.

Methods used to characterize the starting material and the final product

Isomerase activity was determined in International Glucose Isomerase Units, abbreviated GIU, per 1 g of dried enzyme preparation. One unit (GIU) is the amount of enzyme which converts glucose to fructose at a rate of 1 pmol / min under the following conditions: glucose concentration 2.0 mol / l, pH 7.0 and temperature 60 ° C.

For the activity assay, 0.1-1 g of enzyme product (original crystal mass or well-washed cross-linked crystal mass) was mixed with the above substrate solution (100 ml). After a suitable time, e.g. 10 minutes, the fructose content of the solution was determined and the activity was calculated in the above units. The amount of enzyme and the reaction time were chosen so that less than 5% of the total sugar content was formed from fructose so that the measurement result was related to the initial rate of the reaction. The dry matter content of the starting material and the product was determined by a conventional method by drying the samples at 105 ° C to constant weight.

The isomerization process

The crystalline cross-linked enzyme is suitable for use in a conventional manner in a batch isomerization process, in which case the enzyme used after the reaction is separated, for example by filtration, and can be reused if desired.

However, on an industrial scale, it is more preferable to carry out the isomerization as a continuous process, allowing the sugar solution to be isomerized to flow through the enzyme column. By changing the delay time and / or temperature, the isomerization process can be easily controlled. The enzyme operates over a wide temperature range, from freezing to over 100 ° C. However, in addition to the slow reaction at low temperatures, the crystallization of sugar (fructose hydrates as glucose) is a disadvantage. At high temperatures, on the other hand, the destruction of both the enzyme and fructose is considerably accelerated.

Continuous isomerization is typically performed with a column packed with cross-linked enzyme crystals of 100 to 300. The size and height of the column can be varied according to the capacity requirement. In a small column, a bed height of 5 to 50 cm is suitable. The temperature can also be varied within wide limits. Easy to implement is room temperature. If microbiological contamination is a problem, it can be eliminated by raising the temperature to at least about + 60 ° C.

By changing the linear flow rate, the process is easily controlled. The linear flow rate with a small column is 2 to 30 cm / min. For fresh enzyme, a suitable delay time is 1 to 2 min. Operate at atmospheric pressure. The pressure drop is small (<0.2 bar / 50 cm bed). The delay time is controlled by the bed height of the column as well as the flow rate. Raising the temperature accelerates the isomerization reaction.

In a standard industrial process today, the goal is most often a sugar solution in which 40-45% of the sugar is fructose. As the enzyme activity decreases as the column ages, the desired level is maintained by slowing the flow rate.

The following examples further illustrate the invention: Example 1

850 g of glucose isomerase crystal mass crystallized in 10% ammonium sulfate solution according to U.S. Patent 4,699,882 was weighed. To this was added 1000 ml of 10% ammonium sulfate solution buffered with 0.5% sodium phosphate to pH 7.4. The mixture was cooled to 10 ° C. The mixture was stirred continuously with a propeller stirrer using a low speed, 200-400 rpm, to reduce crystal breakage. To the mixture was added 160 ml of 25% glutaraldehyde. After one hour, the reaction was quenched by the addition of 20 L of pure water. Stirring was stopped immediately and the crystalline mass was allowed to settle to the bottom of the vessel for 2 hours. The mother liquor was decanted, taking care to wash away the crystals. The crystal mass was again mixed with 20 L of pure water and the washings were removed by decantation. Washing with water was performed a third time. The wet isomerase crystal mass thus obtained, washed 3 times with water, was used as such in isomerization experiments and activity assays and other studies.

The cross-linked glucose isomerase thus prepared was in a crystalline state (microscopic examination). The crystals were insoluble in water, dilute aqueous solutions of various salts (pH range 2-9), dilute acids (1 mol / l), hot water and hot brine up to 100 ° C, and concentrated glucose, fructose and sugar solutions up to 100 ° C. Up to C. The appearance of the crystals remained unchanged under all the above conditions, whereas instead the non-crosslinked crystalline isomerase dissolved, or precipitated as an amorphous precipitate. The enzymatic activity of the cross-linked isomerase was 52% of the activity of the original, non-cross-linked isomerase, i.e., when the activity of the original isomerase is 40,000 Glu / g, the activity of the cross-linked crystals is more than 20,000 Glu / g, calculated per dried enzyme protein.

Example 2

By the arrangement of Example 1, the following reaction mixture was prepared at 25 ° C:

g isomerase calculated as pure enzyme protein g ammonium sulphate

1.5 g of glutaraldehyde (approx. 8 ml of 25% solution) 0.05 M sodium phosphate buffer (pH 7.4) in 100 ml of water

After a reaction time of one hour, the free solution was removed from the mixture by centrifugation in a laboratory centrifuge for 5 minutes at 1000 rpm. The resulting crystalline mass was slurried in 200 ml of pure water and centrifuged again as above. The washing with water was repeated once more as above. The moist washed crystalline mass was recovered and used for further studies. The activity of the crystal mass thus prepared was 49% of the activity of the original crystal mass.

Examples 3-8

By the arrangement of Example 1, reaction mixtures having the same initial composition as in Example 2 were prepared at 10 ° C. After various reaction times, the reaction was stopped and the crystalline mass was washed, after which the activities of the crystalline masses were determined. The results are shown in Table I:

Table I

Activity (% of initial crystal mass activeReaction time)

<td>Example 3</td><td>10 min</td><td> 45</td>

<td>Example 4</td><td>30 min</td><td> 46</td>

<td>Example 5</td><td>60 min</td><td> 49</td>

<td>Example 6</td><td>90 min</td><td> 48</td>

<td>Example 7</td><td>2 h</td><td> 40</td>

<td>Example 8</td><td>3 h</td><td> 40</td>

Judging from the results, the reaction is completed very quickly and the activity does not change significantly as the reaction times are maintained.

Examples 9-16

By the arrangement of Example 1, reaction mixtures were prepared at 10 ° C with the following initial composition:

g glucose isomerase protein (crystalline) g ammonium sulphate ml 0.5 M sodium phosphate solution (pH 6.0, 7.0, 8.0 or 8.4 as shown in Table II) glutaraldehyde 0.12, 0.5, 2 , 0, 3.5 or 4.12 g (as shown in Table II).

The reaction time was 1 hour. The activity of the obtained crystal masses (as a% of the activity of the initial crystal mass) is shown in Table II).

Table II

<td colspan="2"></td><td>PH</td><td>Glutaraldehyde (g)</td><td>Activity (%)</td>

<td>Example</td><td> 9</td><td> 6,0</td><td> 0,5</td><td> 22</td>

<td>Example</td><td> 10</td><td> 6,0</td><td> 3,5</td><td> 24</td>

<td>Example</td><td> 11</td><td> 7,0</td><td> 0,12</td><td> 60</td>

<td>Example</td><td> 12</td><td> 7,0</td><td> 2,0</td><td> 65</td>

<td>Example</td><td> 13</td><td> 7,0</td><td> 4,12</td><td> 59</td>

<td>Example</td><td> 14</td><td> 8,0</td><td> 0,5</td><td> 41</td>

<td>Example</td><td> 15</td><td> 8,0</td><td> 3,5</td><td> 44</td>

<td>Example</td><td> 16</td><td> 8,4</td><td> 2,0</td><td> 39</td>

From the results, it can be concluded that the amount of glutaraldehyde can be varied within quite wide limits and still good activities can be achieved. Instead, acidity has a strong effect on the result; the most preferred pH is about 7.0, although a useful product can be prepared over the entire pH range studied, 6.0 to 8.4.

Examples 17-27

A series of experiments similar to the previous examples were performed, but with a temperature of 2 ° C and a reaction time of 18 hours. The composition of the reaction mixture was as follows:

g of isomerase crystals as dry protein calculated in ml of water as medium

7.5 g of salt (sodium sulphate, magnesium sulphate and / or ammonium sulphate (see Table III)) sodium hydroxide to adjust the pH to 7.0 (maximum 2 meq, ie 80 mg) glutaraldehyde 0.125-2.5 g (see Table III) .

Table III

<td rowspan="2">Example Example</td><td colspan="4">Salt (g) (NH₄)₂SO₄ MgSO₄ As₂SO₄</td><td rowspan="2">glutaraldehyde (G) 0.5 2.5</td><td rowspan="2">Activity (%) 0 0</td>

<td colspan="2"> 17 18</td><td colspan="2"> 7,5 7,5</td>

<td>Example</td><td> 19</td><td></td><td> 7,5</td><td></td><td> 0,125</td><td> 0</td>

<td>Example</td><td> 20</td><td></td><td> 7,5</td><td></td><td> 0, 5</td><td> 0</td>

<td>Example</td><td> 21</td><td></td><td> 7,5</td><td></td><td> 0,75</td><td> 0</td>

<td>Example</td><td> 22</td><td></td><td> 7,5</td><td></td><td> 1,25</td><td> 0</td>

<td>Example</td><td> 23</td><td> 0,45</td><td> 7,05</td><td></td><td> 0,75</td><td> 20</td>

<td>Example</td><td> 24</td><td> 0,90</td><td> 6,6</td><td></td><td> 0,75</td><td> 19</td>

<td>Example</td><td> 25</td><td> 1,8</td><td> 5,7</td><td></td><td> 0,75</td><td> 28</td>

<td>Example</td><td> 26</td><td> 3,75</td><td> 3,75</td><td></td><td> 0,75</td><td> 40</td>

<td>Example</td><td> 27</td><td> 7,5</td><td></td><td></td><td> 0,75</td><td> 60</td>

It can be concluded from the results that when crosslinked in the absence of the ammonium salt, insoluble crystals are not formed even at high glutaraldehyde content. Instead, even a small amount of ammonium salt promotes the formation of an insoluble crystal.

Examples 28-38

Insoluble isomerase crystals were prepared using several different nitrogen compounds according to the following general procedure:

g of crystalline isomerase calculated as dry protein

7.5 g magnesium sulphate mmol nitrogen compound (see Table IV)

2.5 g of glutaraldehyde (calculated as 100%)

Temperature 2 ° C and reaction time 18 hours

Table IV

<td></td><td>The nitrogen compound</td><td>Amount (g)</td><td>Activity (%)</td>

<td>Example 28</td><td>lysine</td><td> 1,83</td><td> 80</td>

<td>Example 29</td><td>arginine</td><td> 1,74</td><td> 17</td>

<td>Example 30</td><td>histidine</td><td> 1,55</td><td> 26</td>

<td>Example 31</td><td>glutamine</td><td> 1,46</td><td> 18</td>

<td>Example 32</td><td>leucine</td><td> 1,31</td><td> 21</td>

<td>Example 33</td><td>isoleucine</td><td> 1,31</td><td> 18</td>

<td>Example 34</td><td>proline</td><td> 1,15</td><td> 10</td>

<td>Example 35</td><td>methionine</td><td> 1,49</td><td> 27</td>

<td>Example 36</td><td>phenylalanine</td><td> 1,65</td><td> 17</td>

<td>Example 37</td><td>tryptophan</td><td> 2,04</td><td> 44</td>

<td>Example 38</td><td>betaine</td><td> 1,17</td><td> 23</td>

From the results, it can be concluded that a number of different amines have a similar effect on the crosslinking process.

Examples 39-51

Insoluble isomerase crystals were prepared with different doses of glutaraldehyde and lysine according to the following basic procedure:

g of crystalline isomerase calculated as dry protein

7.5 g of magnesium sulphate

0.47-2.34 g of lysine (see Table V) pH adjustment to 8.0 with sodium hydroxide solution

0.5-1.25 g of glutaraldehyde (100%; see Table V)

The reaction was allowed to proceed for 18 hours at 2 ° C.

Table V

<td></td><td>glutaric</td><td>lysine</td><td>activity</td>

<td></td><td>aldehyde (g)</td><td>(G)</td><td> (%)</td>

<td>Example 39</td><td> 0,5</td><td> 0,47</td><td> 67</td>

<td>Example 40</td><td> 0,5</td><td> 0,94</td><td> 77</td>

<td>Example 41</td><td> 0,5</td><td> 1,40</td><td> 60</td>

<td>Example 42</td><td> 0,75</td><td> 0,47</td><td> 72</td>

<td>Example 43</td><td> 0,75</td><td> 0,94</td><td> 83</td>

<td>Example 44</td><td> 0,75</td><td> 1,40</td><td> 92</td>

<td>Example 45</td><td> 0,75</td><td> 1,87</td><td> 81</td>

<td>Example 46</td><td> 0,75</td><td> 2,34</td><td> 75</td>

<td>Example 47</td><td> 1,25</td><td> 0,47</td><td> 68</td>

<td>Example 48</td><td> 1,25</td><td> 0,94</td><td> 78</td>

<td>Example 49</td><td> 1,25</td><td> 1,40</td><td> 90</td>

<td>Example 50</td><td> 1,25</td><td> 1,87</td><td> 102</td>

<td>Example 51</td><td> 1,25</td><td> 2,34</td><td> 100</td>

The results show that the ratio of lysine and glutaraldehyde dosages has an effect on the formation of insoluble crystals, i.e. an optimal lysine dose level can be seen at each glutaraldehyde dosage level.

Examples 52-57

Isomerase crystals were crosslinked in mixtures of anonium sulfate and lysine according to the following general procedure:

g of isomerase crystals in 10% ammonium sulphate (ie 3.72 g of pure isomerase protein calculated as dry matter, 0.63 g of ammonium sulphate and 5.65 g of water) g of ammonium sulphate g of water

1.25 g of glutaraldehyde calculated as 100%, lysine 0-3 g (see Table VI)

The pH of all components of the reaction mixture was adjusted to 8.0 with sodium hydroxide before stirring.

The mixtures were stirred at + 3 ° C for 18 hours.

Table VI

<td></td><td>Lysine (g)</td><td>Activity (%)</td>

<td>Example 52</td><td> 0</td><td> 40</td>

<td>Example 53</td><td> 0,3</td><td> 62</td>

<td>Example 54</td><td> 0,6</td><td> 66</td>

<td>Example 55</td><td> 1,2</td><td> 72</td>

<td>Example 56</td><td> 1,8</td><td> 92</td>

<td>Example 57</td><td> 3,0</td><td> 96</td>

<td>the results of</td><td>it appears that</td><td>lysine is very advantageous</td>

effect on cross-linking yield. Ammonium sulfate is not very important in the result when lysine is available, although ammonium sulfate alone gives a satisfactory result.

Examples 58-69

The amounts of isomerase and lysine were kept constant and the other components were varied according to Table VII:

g glucose isomerase calculated as dry g lysine

0.01 g of sodium hydroxide (pH 8 of the mixture). The reaction time was 18 hours and the temperature was 2 ° C.

Table VIII

<td colspan="2"></td><td>glutaraldehyde (G)</td><td>MgSO₄(G)</td><td>water (G)</td><td>Reaction- a mixture of tot. (g)</td><td>activity (%)</td>

<td>Example</td><td> 58</td><td> 0,5</td><td> 2,1</td><td> 11,9</td><td> 18,5</td><td> 39</td>

<td>Example</td><td> 59</td><td> 0, 5</td><td> 2,7</td><td> 15,3</td><td> 22, 5</td><td> 70</td>

<td>Example</td><td> 60</td><td> 0,5</td><td> 4,2</td><td> 23,8</td><td> 32, 5</td><td> 70</td>

<td>Example</td><td> 61</td><td> 0,5</td><td> 5,3</td><td> 32,7</td><td> 42,5</td><td> 73</td>

<td>Example</td><td> 62</td><td> 0,5</td><td> 10,2</td><td> 57, 8</td><td> 72,5</td><td> 75</td>

<td>Example</td><td> 63</td><td> 0,5</td><td> 16,2</td><td> 91,8</td><td> 112, 5</td><td> 77</td>

<td>Example</td><td> 64</td><td> 1,25</td><td> 2,1</td><td> 11,9</td><td> 19,25</td><td> 86</td>

<td>Example</td><td> 65</td><td> 1,25</td><td> 2,7</td><td> 15,3</td><td> 23,25</td><td> 99</td>

<td>Example</td><td> 66</td><td> 1,25</td><td> 4,2</td><td> 23,8</td><td> 33,25</td><td> 101</td>

<td>Example</td><td> 67</td><td> 1,25</td><td> 5,3</td><td> 32,7</td><td> 43,25</td><td> 89</td>

<td>Example</td><td> 68</td><td> 1,25</td><td> 10,2</td><td> 57,8</td><td> 73,25</td><td> 83</td>

<td>Example</td><td> 69</td><td> 1,25</td><td> 16,2</td><td> 91,8</td><td> 113,25</td><td> 89</td>

The results show that the concentration of the reaction mixture has a relatively small effect on the final result. The weight ratios of the substances involved in the reaction (enzyme, lysine (or amine) and glutaraldehyde) are of much greater importance.

Example 70 g of a water-washed cross-linked glucose isomerase mass (from Example 56; 0.4 g of dry matter) was mixed with 100 g of a 40% glucose solution adjusted to pH 7.0. The mixture was stirred continuously at 60 ° C. The mixture was periodically sampled for fructose content by polarimeter and glucose content enzymatically by hexokinase. The fructose content of the solution increased to 42% of the total sugar content of the mixture (glucose + fructose = 100%) over 3 hours. After the experiment, the cross-linked isomerase was separated from the mixture by filtration and washed with water. The recovered crystal mass was assayed for activity and dry matter content19 and it was found that no active enzyme had dissolved or lost in the experiment. With the same batch of enzyme, this experiment could be repeated numerous times.

Example 71

The crystalline mass prepared according to Example 1 was washed to remove a fine precipitate and any finely ground crystalline crumb in the process by slurrying in water and decanting (3 times). The large crystal fraction thus prepared, having an average size of 100 μm, was packed in a cylindrical reactor having a diameter of 2.6 cm and a height of 5 cm. A glucose solution having the following composition was pumped through the column at 60 ° C:

582 g of glucose monohydrate

590 g of water

0.37 g MgSO 4₄ . 7 H₂ 0

0.19 g NaHSO₃ pH 6.9 (1-m NaOH, consumption less than 1 ml)

At the beginning of the experiment, the flow rate was 11 ml / min, when the fructose content of the solution leaving the column had risen to 42% of the total sugar content. The experiment was continued for 200 hours, after which the flow rate had to be reduced to 9 ml per minute to maintain the initial conversion (fructose content 42%). Thus, the enzyme activity had decreased to 81% of the original during this period. No decrease in crystal mass and dissolution could be observed during the experiment.

Examples 72-76

43.42 g of wet water-washed active isomerase crystal mass (prepared by the method of Example 67; 10.0 g of enzyme as a dry substance) was weighed.

200 ml of the glucose solution prepared according to Example 71 was poured onto the crystal mass. The mixture was shaken at 60 ° C for various lengths of time and then the mixture was filtered through a filter paper disc. There is 20 left on the paper

52 85 now the crystalline mass was washed thoroughly with water to remove any soluble matter. The crystal mass was dried in an oven at 105 ° C and weighed. The findings are presented in Table Vili:

Table VIII

Mixing time Dry weight of crystal mass after test (g)

<td>Example</td><td> 72</td><td> 10</td><td>min</td><td> 9,9</td>

<td>Example</td><td> 73</td><td> 2</td><td>B</td><td> 11,0</td>

<td>Example</td><td> 74</td><td> 4</td><td>B</td><td> 10,9</td>

<td>Example</td><td> 75</td><td> 6</td><td>B</td><td> 10,7</td>

<td>Example</td><td> 76</td><td> 21</td><td>B</td><td> 10,4</td>

The results show that the cross-linked crystalline isomerase prepared by the process of the invention is insoluble in the substrate under normal industrial conditions of use.

Example 77

Cross-linked crystalline isomerase, DEAE-cellulose-bound, and the original free soluble isomerase were compared by keeping them under identical chemical and physical conditions. The conditions were chosen so that all enzyme samples lost measurable activity in a reasonably short time, a few tens of hours. 5 g of each enzyme preparation was mixed with 150 ml of 0.05 M sodium phosphate buffer (pH 6.0) with an additional 1.5 mmol / l MgSO 4.₄ and 2 mmol / l NaHSO₃. The mixture was shaken for several hours at 70 ° C. The mixture was periodically sampled to determine residual isomerase activity. Based on the decrease in activity, the half-life of each enzyme sample (i.e., the time during which the activity is reduced to half of the original) was calculated. The results are shown in Table IX:

Table IX

Enzyme sample Half-life (h)

Initial soluble isomerase2,2

DEAE-cellulose-bound isomerase3,3

Cross-linked crystalline isomerase19.0

The results show that the enzymatic activity is substantially better preserved in the cross-linked crystals than in the free enzyme or in an enzyme immobilized in a known manner.

Example 78

The cross-linked crystalline isomerase and the DEAE-cellulose-bound isomerase were packed in a cylindrical column reactor according to Example 71. A glucose solution having the same composition as in Example 71 was continuously pumped through the columns, except that the pH was adjusted to 6.0. The temperature of the columns during the experiment was 60 ° C. The activity of the enzyme in the columns was calculated based on the flow rate and the fructose content of the solution passed. The results are shown in Table X.

Table X

Reactor packing Activity half - life (h) Cross - linked isomerase crystal mass 120

DEAE-cellulose-bound isomerase 36

The results show that the activity of the enzyme is excellent in the cross-linked crystals.