Effect of sodium nitrite, primaquine, and menadione on TPN-methemoglobin reductase in vitro

The in vitro effect of sodium nitrite, primaquine, and menadione on the triphosphopyridine nucleotide-dependent methemoglobin reductase was investigated using enzyme isolated from human, porcine, and canine blood. This reductase has different salting-out properties among the three species studied. None of the specimens examined were deficient either in this enzyme or in glucose-6-phosphate dehydrogenase. Primaquine and menadione suppress this enzyme whereas sodium nitrite does not. These findings are offered as a partial explanation of the clinical fact that with some drugs, such as sodium nitrite, one may observe methemoglobinemia without hemolysis, while with other drugs, such as primaquine and menadione, hemolysis follows methemoglobinemia.