Methemoglobinemia Diaphorase

On the other hand, highly purified preparations (180-fold) obtained by Huennekens and his co-workers (H22) have been shown to be a hemo-protein with a molecular weight of approximately 185,000. With regard to these different results it is interesting that in RBC of individuals suffering from hereditary methemoglobinemia a complete lack of NAD diaphorase has been reported (S10, Sll) this would indicate the importance of an enzyme which contains FAD. The reasons for the discrepancies between the preparations obtained by two teams of investigators are not understood as yet. Perhaps they are implicated in the electron transport mechanisms or in the nature of a certain cofactor which is to be discussed now. 

Scott, E. M., The relation of diaphorase of human erythrocytes to inheritance of methemoglobinemia. J. Clin. Invest. 39, 1176-1179 (I960). 

Methemoglobinemia has long been associated with the absence of an NADH-linked diaphorase 362, 363). However, flavoproteins isolated from the red cell were never sufficiently active to account for the methemoglobin reductase activity calculated to be necessary. It has now been shown that a methemoglobin reductase system of high activity is composed of soluble forms of cytochrome bj reductase and cytochrome bs... 

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