A NEW KINETIC-MODEL FOR THE MODE OF ACTION OF SOLUBLE AND MEMBRANE-IMMOBILIZED GLUTATHIONE-PEROXIDASE FROM BOVINE ERYTHROCYTES - EFFECTS OFSELENIUM

Kinetic studies on the oxidative reaction of glutathione by hydrogen p eroxide were performed using soluble and membrane-bound ox erythrocyte glutathione peroxidase of various types. The effects of organic and i norganic selenium on the glutathione peroxidase activity were also exa mined. The kinetic behaviour of the enzyme was investigated using a co upled reaction within a relatively large range of hydrogen peroxide an d glutathione concentrations. Non-parallel double-reciprocal plots wer e obtained which suggested that a sequential ordered rather than a pin g-pong mechanism was involved. Similar results were obtained with solu ble and membrane-bound enzyme, whatever the type of crosslinking used. Crosslinking was performed on a nylon support using various alkylatin g agents and bifunctional molecules, With all three types of immobiliz ed enzyme thus obtained, a slight but significant increase in the k(m) was observed. The effects of selenium were then studied. Using solubl e enzyme, a slight increase in the activity was observed in the presen ce of inorganic selenium (sodium selenite) but not with organic seleni um (seleno-L-methionine). Inorganic selenium alone was also found to h ave a slight effect on the membrane-bound enzyme. An increase in the c atalytic efficiency was observed when glutathione: peroxidase was boun d using lysine as the bifunctional agent and either glutaraldehyde or triethyloxonium tetrafluoroborate as the reticulation agent, after a t hree-month period of incubation.