Species differences in methemoglobin reductase activity

Abstract

Sodium nitrite induced equivalent levels of methemoglobin in washed erythrocytes from cat, dog, and man, all suspended in Krebs-Ringer phosphate-glucose (pH 7·4). The same levels occurred in human cells with or without aded substrate (glucose or lactate). In all these incubations, reduction of methemoglobin was minimal or absent over a 2-hr period. When 10 −5M methylene blue was added with glucose, equivalent increases in rates of methemoglobin reduction occurred in the cells of all three species. Similar rates were seen in rabbit and mouse red cells even without added methylene blue, as long as lactate or glucose was present. Methylene blue further enhanced reductase activity in mouse cells but only in the presence of glucose. Rabbit cells responded much less dramatically, if at all, to methylene blue. Lysates of human, rabbit, and mouse cells were equally sensitive to nitrite, and no spontaneous reduction occurred. These findings suggest that the high reductase activity of rabbit and mouse erythrocytes is NADH-dependent. The mouse but not the rabbit appears to possess also a NADPH-dependent reductase like man, dog and cat.