Immobilized xanthine oxidase: Kinetics, (in)stability,and stabilization by coimmobilization with superoxide dismutase and catalase

Milk xanthine oxidase was immobilized by covalent attachment to CNBr-activated Sepharose 4B and by adsorption to n-octylamine-substituted Sepharose 4B. The amounts of activity immobilized for the two preparations were 30 and 90%, respectively. The pH optima for free and adsorbed xanthine oxidase were at 8.6 and 8.2, respectively. Both free and immobilized xanthine oxidase show substrate inhibition. The apparent inhibition constant (K_i′) found for adsorbed xanthine oxidase with xanthine as substrate was higher than the K_i for the free enzyme, which was shown to be due to substrate diffusion limitation in the pores of the carrier beads (internal diffusion limitation). Higher substrate concentrations, as desirable for practical application in organic synthesis, can therefore be used with the immobilized enzyme without decreasing the rate. As a result of the internal diffusion limitation the apparent Michaelis constant (K_m′) for adsorbed xanthine oxidase was also higher than the K_m for the free enzyme. Immobilized xanthine oxidase was more stable than the free enzyme during storage at 4 and 30°C. Both forms rapidly lost activity during catalysis. The loss was proportional to the amount of substrate converted. Coimmobilization of xanthine oxidase with superoxide dismutase and catalase improved the operational stability, suggesting that O₂^? and H₂O₂ side-products of the enzymatic reaction were involved in the inactivation. Coimmobilization with albumin also had some stabilizing effect. Complete surrounding of xanthine oxidase by protein, however, by means of etrapment in a glutaraldehyde-crosslinked gelatin matrix, considerably enhanced the operational half-life. This system was less efficient than the Sepharose preparations either because much activity was lost during the immobilization procedure and/or because it had poor flow properties. Xanthine (15 mg)was converted by an adsorbed xanthine oxidase preparation and product (uric acid) was isolated in high yield (84%).     

Kinetics and stability of immobilized chicken liver xanthine dehydrogenase.

Xanthine dehydrogenase (EC 1.2.1.37) was isolated from chicken livers and immobilized by adsorption to a Sepharose derivative, prepared by reaction of n-octylamine with CNBr-activated Sepharose 4B. Using a crude preparation of enzyme for immobilization it was observed that relatively more activity was adsorbed than protein, but the yield of immobilized activity increased as a purer enzyme preparation was used. As more activity and protein were bound, relatively less immobilized activity was recovered. This effect was probably due to blocking of active xanthine dehydrogenase by protein impurities. The kinetics of free and immobilized xanthine dehydrogenase were studied in the pH range 7.5-9.1. The Km and V values estimated for free xanthine dehydrogenase increase as the pH increase; the K'm and V values for the immobilized enzyme go through a minimum at pH 8.1. By varying the amount of enzyme activity bound per unit volume of gel, it was shown that K'm is larger than Km are result of substrate diffusion limitation in the pores of the support material. Both free and immobilized xanthine dehydrogenase showed substrate activation at low concentrations (up to 2 microM xanthine). Immobilized xanthine dehydrogenase was more stable than the free enzyme during storage in the temperature range of 4-50 degrees C. The operational stability of immobilized xanthine dehydrogenase at 30 degrees C was two orders of magnitude smaller than the storage stability, t 1/2 was 9 and 800 hr, respectively. The operational stability was, however, better than than of immobilized milk xanthine oxidase (t 1/2 = 1 hr). In addition, the amount of product formed per unit initial activity in one half-life, was higher for immobilized xanthine dehydrogenase than for immobilized xanthine oxidase. Unless immobilized milk xanthine oxidase can be considerable stabilized, immobilized chicken liver xanthine dehydrogenase is more promising for application in organic synthesis.     

Preparation of an alcohol-dehydrogenase--NAD(H)--sepharose complex showing no requirement of soluble coenzyme for its activity.

1. Horse liver alcohol dehydrogenase and an NADH analogue, N6-[(6-aminohexyl)carbamoylmethyl]-NADH, have been co-immobilized to Sepharose 4B under conditions permitting binary complex formation between the enzyme and the cofactor. 2. The enzyme-coenzyme-matrix preparations were assayed with a coupled oxidoreduction reaction and showed activities, prior to addition of coenzyme, that were up to 40% of that obtained in excess of free coenzyme. 3. A molar ratio of 1:1 between the amount of bound enzyme was sufficient to obtain high activities in the absence of free coenzyme. 4. The highest recycling rate obtained for the immobilized nucleotide was 3400 cycles per hour. 5. Both thermal and storage stability of alcohol dehydrogenase was increased when the enzyme was co-immobilized with the NADH analogue. 6. The efficiency of the immobilized preparations (measured as product formation per minute and per assay volume) was higher (1.4 to 5 times in our assays) than the corresponding systems of free enzyme (in total enzyme units) and nucleotide in an identical assay volume.     

The effect of lead on the calcium-handling capacity of rat heart mitochondria.

1. Glucose 6-phosphate dehydrogenase (D-glucose 6-phosphate-NADP+ oxidoreductase, EC 1.1.1.49) from baker's yeast (Saccharomyces cerevisiae) was immobilized on CNBr-activated Sepharose 4B with retention of about 3% of enzyme activity. This uncharged preparation was stable for up to 4 months when stored in borate buffer, pH7.6, at 4 degrees C. 2. Stable enzyme preparations with negative or positive overall charge were made by adding valine or ethylenediamine to the CNBr-activated Sepharose 4B 30min after addition of the enzyme. 3. These three immobilized enzyme preparations retained 40-60% of their activity after 15 min at 50 degrees C. The soluble enzyme is inactivated by these conditions. 4. The soluble enzyme lost 45 and 100% of its activity on incubation for 3h at pH6 and 10 respectively. The three immobilized-enzyme preparations were completely stable over this entire pH range. 5. The pH optimum of the positively and negatively charged immobilized-enzyme preparations were about 8 and 9 respectively. The soluble enzyme and the uncharged immobilized enzyme had an optimum pH at about 8.5 6. Glucose 6-phosphate dehydrogenase immobilized on CNBr-activated Sephadex G-25 was unstable, as was enzyme attached to CNBr-activated Sepharose 4B to which glycine, asparitic acid, valine or ethylenediamine was added at the same time as the enzyme.     

Stabilization of soluble and immobilized horse liver alcohol dehydrogenase by adenosine 5'-monophosphate

Horse liver alcohol dehydrogenase, which catalyzes oxidoreductions for a broad spectrum of substrates of organic chemical interest, was immobilized on CNBr-activated Sepharose and on decylamine-substituted agarose. The specific activities of the immobilized enzyme preparations were compared with the free enzyme, and the apparent K(m) values of the preparations were determined for a selection of substrates. At pH 9 and 60 degrees C, soluble liver alcohol dehydrogenase was rapidly inactivated, while the enzyme immobilized on CNBr-activated Sepharose was more stable. Adenosine monophosphate (AMP), adenosine diphosphate, and adenosine diphosphoribose protected the free and immobilized alcohol dehydrogenase against heat inactivation. On storage under a variety of conditions, AMP effectively stabilized free horse liver alcohol dehydrogenase and the immobilized preparations.     

Studies on the stability of immobilized xanthine oxidase and urate oxidase.

The stability of immobilized preparations of xanthine oxidase and urate oxidase was studied, and optimized, because of the potential joint use of both enzymes in clinical analysis. Xanthine oxidase was immobilized on cellulose, Sepharose, hornblende, Enzacryl-TIO, and porous glass. Thehalf-lives of these preparations at 30 degree C ranged from 40 min to 5.0 hr. In this respect immobilized enzyme resembled soluble enzyme in dilute solution (0.11 mg/ml), when the half-live was about 3.5 hr. More concentrated enzyme solution (1 mg/ml) had a half-life of 64 hr, and was, therefore, considerably more stable than the untreated immobilized xanthine oxidase preparations. Inclusion of albumen in storage and assay buffer increased the half-life of bound xanthine oxidase. So also did treatment with glutaraldehyde: in the case of xanthine oxidase bound to Enzarcyl-TIO such treatment increased the half-life at 30 degree C from 3 hr to about 100 hr. Immobilized xanthine dehydrogenase was more stable than immobilized xanthine oxidase: the dehydrogenase lost no activity during continuous assay for 5 hr at 30 degree C. The stability of immobilized urate oxidase depended on the quantity of enzyme used and on the time of stirring during immobilization: thus a preparation was made (by stirring urate oxidase (48 mg/g support) with Enzacryl-TIO for 24 hr) which lost no activity during 350 hr at 30 degree C.     

Immobilization of glycoenzymes through carbohydrate side chains.

Glucoamylase, peroxidase, glucose oxidase, and carboxypeptidase Y were covalently bound to water-insoluble supports through their carbohydrate side chains. Two approaches were used. First, the carbohydrate portions of the enzymes were oxidized with periodate to generate aldehyde groups. Treatment with amines (ethylenediamine or glycyltyrosine) and borohydride provided groups through which the protein could be immobilized. Ethylenediamine was attached to glucoamylase, peroxidase, glucose oxidase, and carboxypeptidase Y to the extent of 24, 20, 30, and 15 mol/mol of enzyme, respectively. These derivatives were coupled to an aminocaproate adduct of CL-Sepharose via an N-hydroxysuccinimide ester or to CNBr-activated Sepharose. Coupling yields were in the range of 37–50%. Retained activities of the bound aminoalkyl-enzymes were 41% (glucoamylase), 79% (peroxidase), 71% (glucose oxidase), 83% (carboxypeptidase Y). A glycyltyrosine derivative of carboxypeptidase Y was bound to diazotized arylamine-glass. Coupling yield was 42% and retained esterase activity was 84%. In the second approach, the enzyme was adsorbed to immobilized concanavalin A and the complex was crosslinked. Adsorption of carboxypeptidase Y on immobilized concanavalin A followed by crosslinking with glutaraldehyde was also effective. The bound enzyme retained 96% of the native esterase activity and showed very good operational stability.     

Porphyrin biosynthesis: immobilized enzymes and ligands. VI. Studies on succinyl CoA synthetase from cultured soya bean cells

Soybean callus succinyl CoA synthetase (succinate: CoA ligase, (ADP-forming), EC 6.2.1.5), has been chemically bound to Sepharose 4B and some of its properties have been studied. The optimal conditions for binding have been determined. The immobilized enzyme retained 48% of the activity of the soluble enzyme and the coupling yield amounted to 50%. Sepharose-succinyl CoA synthetase can be stored at 4 degrees C for periods up to 90 days with only 25% loss of activity; it can also be repeatedly used without alteration of its enzymic activity. The complex showed enhanced thermal stability; pH optimum was between 7.0 and 8.0 for the bound enzyme, and 8.0 for the free enzyme. A general decrease in the Michaelis-Menten constants for the different substrates of the insoluble enzyme, as compared with values obtained for the free enzyme, was found. Plots of the rate product formation against ATP concentration changed from sigmoideal for the soluble succinyl CoA synthetase to hyperbolic for the immobilized enzyme.     

Immobilization of Escherichia coli cells containing aspartase activity with kappa-carrageenan. Enzymic properties and application for L-aspartic acid production.

Whole cells of Escherichia coli having high aspartase (L-asparate ammonialyase, EC 4.3.1.1) activity were immobilized by entrapping into a kappa-carrageenan gel. The obtained immobilized cells were treated with glutaraldehyde or with glutaraldehyde and hexamethylenediamine. The enzymic properties of three immobilized cell preparations were investigated, and compared with those of the soluble aspartate. The optimum pH of the aspartase reaction was 9.0 for the three immobilized cell preparations and 9.5 for the soluble enzyme. The optimum temperature for three immobilized cell preparations was 5--10 degrees C higher than that for the soluble enzyme. The apparent Km values of immobilized cell preparations were about five times higher than that of the soluble enzyme. The heat stability of intact cells was increased by immobilization. The operational stability of the immobilized cell columns was higher at pH 8.5 than at optimum pH of the aspartase reaction. From the column effluents, L-aspartic acid was obtained in a good yield.     

Immobilization of nucleoside diphosphatase at its allosteric site using immobilized derivatives of pyridoxal 5'-phosphate

3-O-Immobilized and 6-immobilized pyridoxal 5′-phosphate analogs of Sepharose were bound to the allosteric site of nucleoside diphosphatase with very high affinity. Active immobilized nucleoside diphosphatase was prepared by reduction of the Schiff base linkage between the enzyme and pyridoxal 5′-phosphate bound to Sepharose with NaBH₄. 3-O-Immobilized pyridoxal 5′-phosphate analog gave more active immobilized enzyme than the 6-analog; the immobilized enzyme on the 3-O-immobilized pyridoxal 5′-phosphate analog showed about 90% of activity of free enzyme. The immobilized enzyme thus prepared was less sensitive to ATP, an allosteric effector, and showed a higher heat stability than the free enzyme. When an assay mixture containing inosine diphosphate and MgCl₂ was passed through a column of the immobilized enzyme at 37 °C, inosine diphosphate liberated inorganic phosphate almost quantitatively. Properties of the immobilized enzyme on the pyridoxal 5′-phosphate analog were compared with those of the immobilized enzyme on CNBr-activated Sepharose.     

Studies on oxalate oxidase from beet stems upon immobilization on concanavalin A.

Oxalate oxidase (EC 1.2.3.4) was purified from beet stems and immobilized on concanavalin A. The bound enzyme showed a high resistance of denaturation and increased the storage stability at 4 degrees C. The immobilized oxidase showed a broad optimum at pH 3.5-5, compared to the free enzyme with a sharp optimum at pH 4.5. There was a 3-fold increase in the apparent Km value on immobilization. The lectin interaction also eliminated the inhibitory effect produced on the enzyme by azide, nitrate and glycollate. The stimulatory effect on the enzyme activity by the flavins was not seen with the bound enzyme. The interaction of oxidase on concanavalin A-Sepharose 4B column and its reversal with methyl alpha-D-mannoside, indicated the presence of polysaccharides. The glycoprotein nature was further confirmed by periodic acid-sciff staining procedure of the enzyme after gel electrophoresis.     

Immobilization of d-glucose oxidase onto a hydrogen peroxide permselective membrane and application for an enzyme electrode

A hydrogen peroxide permselective membrane with asymmetric structure was prepared and d-glucose oxidase (EC 1.1.3.4) was immobilized onto the porous layer. The activity of the immobilized d-glucose oxidase membrane was 0.34 units cm^?2 and the activity yield was 6.8% of that of the native enzyme. Optimum pH, optimum temperature, pH stability and temperature stability were found to be pH 5.0, 30–40°C, pH 4.0–7.0 and below 55°C, respectively. The apparent Michaelis constant of the immobilized d-glucose oxidase membrane was 1.6 × 10^?3 mol l^?1 and that of free enzyme was 4.8 × 10^?2 mol l^?1. An enzyme electrode was constructed by combination of a hydrogen peroxide electrode with the immobilized d-glucose oxidase membrane. The enzyme electrode responded linearly to d-glucose over the concentration 0–1000 mg dl^?1 within 10 s. When the enzyme electrode was applied to the determination of d-glucose in human serum, within day precision (CV) was 1.29% for d-glucose concentration with a mean value of 106.8 mg dl^?1. The correlation coefficient between the enzyme electrode method and the conventional colorimetric method using a free enzyme was 0.984. The immobilized d-glucose oxidase membrane was sufficiently stable to perform 1000 assays (2 to 4 weeks operation) for the determination of d-glucose in human whole blood. The dried membrane retained 77% of its initial activity after storage at 4°C for 16 months.     

Structure-function relationships in immobilized chymotrypsin catalysis

Specific activities and the amounts of active immobilized enzyme were determined for several different preparations of alpha-chymotrypsin immobilized on CNBr-activated Sepharose 4B. Electron paramagnetic resonance (EPR) spectroscopy of free and immobilized enzyme with a spin label coupled to the active site was used to probe the effects of different immobilization conditions on the immobilized enzyme active site configuration. Specific activity of active enzyme decreased and rotational correlation time of the spin label increased with increasing immobilized enzyme loading. Enzyme immobilized using an intermediate six-carbon spacer arm exhibited greater specific activity and spin label mobility than directly coupled enzyme. The observed activity changes due to immobilization were completely consistent with corresponding active site structure alterations revealed by EPR spectroscopy.     

Structure-function relationships in immobilized chymotrypsin catalysis

Specific activities and the amounts of active immobilized enzyme were determined for several different preparations of alpha-chymotrypsin immobilized on CNBr-activated Sepharose 4B. Electron paramagnetic resonance (EPR) spectroscopy of free and immobilized enzyme with a spin label coupled to the active site was used to probe the effects of different immobilization conditions on the immobilized enzyme active site configuration. Specific activity of active enzyme decreased and rotational correlation time of the spin label increased with increasing immobilized enzyme loading. Enzyme immobilized using an intermediate six-carbon spacer arm exhibited greater specific activity and spin label mobility than directly coupled enzyme. The observed activity changes due to immobilization were completely consistent with corresponding active site structure alterations revealed by EPR spectroscopy.     

Immobilized diol dehydrase and its use in studies of cobalamin binding and subunit interaction.

Coenzyme B12 dependent diol dehydrase from Aerobacter aerogenes was immobilized by covalent binding to CNBr-activated Sepharose 4B. The Sepharose-bound enzyme exhibited a markedly high catalytic activity, viz., 75-95% of the specific activity of the original free enzyme. The apoenzyme acquired much greater stability to heat by immobilization. No significant difference between the immobilized and free enzymes was observed in the following properties: the affinity for coenzyme B12; the sensitivity to a sulfhydryl-modifying agent; the absolute requirement for a certain monovalent cation, such as K+, for catalysis; the susceptibility toward oxygen upon incubation with coenzyme B12 in the absence of substrate. These results suggest that the structure and function of the enzyme are not significantly influenced by immobilization on Sepharose. The immobilized enzyme was found to provide a convenient method for a study of ligand interaction with the enzyme. The subunit interaction between two dissimilar subunits, components F and S, was investigated using the component S immobilized on CNBr-activited Sepharose and free component F, and it was demonstrated that the substrate (1,2-propanedoil) promotes the hybrid formation between component F and component S, but K+ alone rather retarded the subunit association to some extent. Na+ markedly weakens the forces which bind the subunits together. The relationship between cobalamin binding and subunit structure is also discussed.     

Immobilization of enzymes in porous supports: Effects of support-enzyme solution contacting

Proteins have been immobilized in porous support particles held in a fixed-bed reactor through which protein solution is continuously circulated. Changing the recirculation flow rate alters the observed immobilization kinetics and the maximum enzyme loading which can be achieved for glucose oxidase and glucoamylase on carbodiimide-treated activated carbon and for glucoamylase immobilized on CNBr-Sepharose 4B. Direct microscopic examination of FITC-labelled protein in sectioned Sepharose particles and indirect activity-loading studies with activated carbon-enzyme conjugates all indicate that immobilized enzyme is increasingly localized near the outer surface of the support particles at larger recirculation flow rates. Restricted diffusion of enzymes may be implicated in this phenomenon. These contacting effects may be significant considerations in the scaleup of processes for protein impregnation in porous supports, since apparent activity and stability of the final preparation depend on internal protein distribution.     

Method of purification of glucose oxidase by means of affinity chromatography on immunoabsorbent]

The possibility to purify glucose oxidase from Penicillium vitale on immunosorbent containing specific antibodies to the enzyme covalently bound with Sepharose 4B is studied. The method of affinity chromatography was applied, beside routine methods of fractionating blood serum proteins, to isolate specific antibodies from antiserum of rabbits immunized with glucose oxidase. Immobilized on Sepharose glucose oxidase was used as biospecific sorbent. Specific antibodies to the enzyme were isolated using chromatograpy of gamma-globulins mixture followed by protein desorption from the column with 1 M NaC1 and 3% glucose. Antibodies were immobilized by their covalent binding to activated Sepharose. The immunosorbent obtained was used to purify low active preparation of glucose oxidase by means of affinity chromatography under conditions worked out for the antibodies isolation. The enzyme was eluted from the column with 1 M NaC1 (pH 3.0) containing 3% glucose. 5-Fold purified enzyme preparation was isolated.     

Activity and operational stability of immobilized mandelonitrile lyase in methanol/water mixtures

Summary The enzyme mandelonitrile lyase was covalently immobilized on solid support materials using different methods. Immobilization on porous silica using coupling with glutaraldehyde afforded preparations with high enzyme loading (up to 9% (w/w)). The immobilized enzyme was used in a packed bed reactor for the continuous production of d-mandelonitrile from benzaldehyde and cyanide. The influence of the flow rate, pH, substrate concentrations and enzyme loading on the reaction yield and the enantiomeric purity of the product was investigated. In order to suppress the competing spontaneous reaction, the enzymatic reaction must be rapid. A flow rate of 9.5 ml/min (0.1 M benzaldehyde and 0.3 M HCN) through a 3 ml reactor afforded a 86% yield of mandelonitrile with 92% enantiomeric excess. No leakage of enzyme occurred under continuous operation. One column was used continuously for 200 h without any decrease in yield or enantiomeric purity of the product. High concentrations of benzoic acid were shown to decrease the operational stability of the system.     

Enhanced stabilization of mungbean thiol protease immobilized on glutaraldehyde-activated chitosan beads

A thiol protease purified from mungbean seedlings was immobilized on chitosan beads cross-linked with glutaraldehyde. The yield of the immobilized enzyme was maximum (～99%) at 1% concentration each of chitosan and glutaraldehyde. The immobilized enzyme showed reusability for 15 batch reactions. Immobilization shifted the optimum pH of the enzyme to a more acidic range and enhanced its stability both at acidic as well as alkaline pH values compared to the free enzyme. The stability of the enzyme to temperature and in aqueous non-conventional medium (ethanol and DMSO) was significantly improved by the immobilization process. The immobilized enzyme exhibited mass transfer limitation reflected by a higher apparent K_m value. This study produced an immobilized biocatalyst having improved characteristics and better operational stability than the soluble enzyme. The increase in stability in the presence of high concentrations of ethanol and DMSO may make it useful for catalyzing organic reactions such as trans-esterification and trans-amidation similar to other cysteine proteinases.     

Some properties of cathepsins chemically fixed to carriers.

An insoluble preparation of rat liver cathepsin D was obtained by coupling the enzyme to Enzacryl Polyacetal (EPA-cathepsin) and to CNBr-activated Sepharose 4B. EPA-cathepsin was active toward the synthetic hexapeptides (Gly-Phe-Leu)2 and did not split hemoglobin. The optimum pH of splitting was displaced upward by 1.5 units to pH 5.0. The enzyme exhibited maximum activity at 60 degrees C. No appreciable loss of activity was seen on storage of the enzyme for 4 months or after repeated use of the preparations. Coupling of rat liver cathepsin D to activated Sepharose gave preparations active towards both protein and synthetic substrates. The preparations were totally inactive in acid media and exhibited maximum activity at pH 7.0, that is, under physiological conditions. Optimum temperature was 65 degrees. The specific activity of the preparations (pH 7.0, 65 degrees) was 60-110 percent that of the free enzyme in acid media. Proteolytic activity of the Sepharose-coupled cathepsin D was not inhibited by pepstatin, whereas that of the free enzyme was fully inhibited by this reagent. A sarcoma cathepsin, similar in some of its properties to the rat liver enzyme, was also coupled to CNBr-activated Sepharose 4B. The preparation split protein substrates at pH 7.0 and possessed enhanced thermostability. The enzymes fixed on Sepharose showed increased stability.