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A new kinetic model for the mode of action of soluble and membrane-immobilized glutathione peroxidase from bovine erythrocytes--effects of selenium.

Kinetic studies on the oxidative reaction of glutathione by hydrogen peroxide were performed using soluble and membrane-bound ox erythrocyte glutathione peroxidase of various types. The effects of organic and inorganic selenium on the glutathione peroxidase activity were also examined. The kinetic behaviour of the enzyme was investigated using a coupled reaction within a relatively large range of hydrogen peroxide and glutathione concentrations. Non-parallel double-reciprocal plots were obtained which suggested that a sequential ordered rather than a ping-pong mechanism was involved. Similar results were obtained with soluble and membrane-bound enzyme, whatever the type of crosslinking used. Crosslinking was performed on a nylon support using various alkylating agents and bifunctional molecules. With all three types of immobilized enzyme thus obtained, a slight but significant increase in the Km was observed. The effects of selenium were then studied. Using soluble enzyme, a slight increase in the activity was observed in the presence of inorganic selenium (sodium selenite) but not with organic selenium (seleno-L-methionine). Inorganic selenium alone was also found to have a slight effect on the membrane-bound enzyme. An increase in the catalytic efficiency was observed when glutathione peroxidase was bound using lysine as the bifunctional agent and either glutaraldehyde or triethyloxonium tetrafluoroborate as the reticulation agent, after a three-month period of incubation.