Glucose oxidase was immobilized both independently and together with catalase in gel of polyvinylalcohol (PVA) in the form of membranes on cotton base (CB). Temperature and pH effects on the activity of immobilized glucose oxidase preparations were studied. The latter were found to have the temperature and pH optimum of the soluble enzyme but with a larger range of action in the area of higher temperatures and pH values. The immobilized glucose oxidase was characterized by increased thermal and pH stabilities. Rate constants of thermal and pH inactivation of the free and immobilized forms of the enzyme were also determined. Calcium ions and casein were found to cause a substantial increase in the activity of immobilized preparations of glucose oxidase. Combined immobilized preparations of glucose oxidase and catalase were used for oxidation of solutions of D-glucose to D-gluconic acid carried out repeatedly for a period of four months with retention of their initial activity.Enzyme preparations immobilized of glucose oxidase and catalase are a convenient form for a reuse in the production of D-gluconic acid from D-glucose, elimination of glucose traces or oxygen from foodstuffs, analysis of glucose in biological liquids, etc.A number of studies have been carried out on the immobilization of glucose oxidase and catalase by incorporating them in gels such as p~lyacrylamide,~-~ ~o l l a g e n ,~ etc. The application of preparations immobilized in polyacrylamide gel to food industry is limited and undesirable.Polyvinylalcohol is better in this respect since as a carrier it is easily available, nontoxic, and forms membranes with large surface areas suitable for enzyme reactions.'-' All these advantages favor the employment of PVA immobilized preparations in food and pharmaceutical industries. The aim of this work was to investigate some properties of glucose oxidase immobilized in PVA gel as well as the use of the corresponding immobilized preparations in the production of D-gluconic acid and its salts. EXPERIMENTALGlucose oxidase was from Penicilium vitale with activity of 80 U/mg. PVA Mowiol with a degree of polymerization of 28 and degree of saponification of 99 used as carrier was a product of Hoechst (City, FRG). Glucose substrate was purchased from Merck (City, FRG). Glutaraldehyde (GA) (50% solution) was obtained from Fluka (Switzerland). The other reagents were commercial products of high purity.The activity of the soluble and immobilized forms of glucose oxidase was measured according to the method of Degtyar' based on iodometric determination of the amount of hydrogen peroxide formed. One activity unit was defined as the amount of enzyme securing consumption of 22.4 p L oxygen for 1 min at optimum conditions (20°C, pH 5.5, excess of oxygen and glucose). ImmobilizationOne milliliter of aqueous solutions containing 2.5, 5.0, 10.0, 20.0 and 40.0 mg glucose oxidase, respectively, was added to samples of 5 mL 5% aqueous PVA solution (ca. pH 7). Those gel-forming solutions were dried in Petri dishes to give dry...

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