抄録
Two NADH diaphorases, diaphorase I and II were isolated and purified from normal and congenital methemoglobinemic erythrocytes by column chromatography, and the relation between diaphorase activities and those of methemoglobin reduction was studied. Activities of diaphorase I for methemoglobinemic red cells were 80% and those of diaphorase II less than 5%, as compared with those for normal ones.
For both erythrocytes, normal and methemoglobinemic, cytochrome b5 reductase activities were detected only in diaphorase II fractions.
The cytochrome b5 reductase deficiency, might lead to the increase in methemoglobin through the decrease in the enzymatic cytochrome b5 reduction and subsequent nonenzymatic reduction of methemoglobin by the reduced cytochrome b5. In order to study the nature of enzyme deficiency in congenital methemoglobinemia, the diaphorase II fraction, obtained from methemoglobinemic cells was concentrated and examined. The methemoglobinemic and normal diaphorase II were without difference concerning Kms for the substrates (the dye and NADH), heat stability, pH response, and electrophoretic pattern.
The ratio of the diaphorase activity to the cytochrome b5 reductase activity was identical for the both enzymes. The production of an abnormal enzyme molecule by silent substitution could not be denied, but in this case the rate of synthesis of the normal enzyme might be decreased.
