The influence of peroxide-stabilizing agents on enzyme deactivation by H2O2

Degradation of oxalate in rats implanted with immobilized oxalate oxidase

Accumulation of oxalate leads to hyperoxaluria and calcium oxalate nephrolithiasis in man. Since oxalate is a metabolic end product in mammals, the feasibility of its enzymic degradation has been tested in vivo in rats by administering exogenous oxalate oxidase. Oxalate oxidase, isolated from banana fruit peels, in its native form was found to be non-active at the physiological pH of the recipient animal. However, its functional viability in the recipient animal was ensured by its prior binding with ethylenemaleic anhydride, thus shifting its pH activity curve towards the alkaline range. Rats implanted with dialysis membrane capsules containing such immobilized oxalate oxidase in their peritoneal cavities effectively metabolized intraperitoneally injected [14C]oxalate as well as its precursor [14C]glyoxalate. The implantation of capsules containing coentrapped multienzyme preparations of oxalate oxidase, catalase and peroxidase led to a further degradation of administered [14C]oxalate in rats.

Oxygen supply to bacterial suspensions of high cell densities by hydrogen peroxide

The supply of heterotrophically growing suspensions of Alcaligenes eutrophus PHB-4 with oxygen formed by the continuous addition of H2O2 in the presence of bovine liver catalase was found to be restricted to well-defined conditions. The catalase-H2O2 system proved to be suitable during the growth at low cell densities equivalent to 2 g dry weight/liter. When under these conditions the oxygen concentration was held constant at 1.8 mg O2/liter, the cells grew for 6-8 hr at a rate almost identical to that observed with conventional aeration. However, aeration with H2O2 for longer durations (10-20 hr) and at higher cell densities (5-20 g dry weight/liter) led invariably to cell damage and retardation of growth. The impairment of growth observed during the oxygen supply by the catalase-H2O2 system was traced back to the formation of gradually increasing steady-state concentrations of H2O2 in the medium. Possible sites of cell damage by H2O2 such as membrane function, excretion and function of siderophores, and synthesis of cell polymers have been studied, and the cytotoxic mechanism of low concentrations of H2O2 was discussed.

Applications of purification reactions for minimizing reaction-generated enzyme poisoning

A mathematical model has been employed to examine the interplay of reaction and mass transfer in immobilized enzyme systems involving reaction-generated enzyme poisions. Deactivation rates can be significantly reduced in some cases by catalyzing a purification reaction in which the poison is transformed into an innocuous substance. This conclusion in illustrated experimentally for reaction-generated H2O2 in a continuous-flow stirred slurry reactor containing glucose oxidase immobilized on activated carbon.