Mammalian erythrocyte glutathione reductase: kinetic constants and saturation with cofactor

Glutathione reductase (GR) was studied in erythrocytes of horses, cats, dogs, and man. Glutathione reductase activity was measured in hemolysates with and without preincubation of hemolysates with flavinadenine dinucleotide. The percentage saturation of GR apoenzyme with cofactor (flavin-adenine dinucleotide) was lower in cats and dogs than in horses or man. The greatest amount of inactive apoenzyme was in feline erythrocytes. Total GR activity listed in order by species is cat greater than man greater than dog greater than horse. Kinetic constants for oxidized glutathione and reduced nicotinamide-adenine dinucleotide phosphate were determined in each species. Although kinetic constant (reduced nicotinamide-adenine dinucleotide phosphate) values for GR were similar, considerable species variation was observed in the kinetic constant (oxidized glutathione) for GR. The kinetic constant (oxidized glutathione) for equine GR was approximately 3 times that for human GR, with intermediate values determined for feline and canine GR.