Human erythrocyte aldehyde dehydrogenase was purified to homogeneity. The enzyme exhibited a single band of activity on starch gel electrophoresis and on isoelectric focusing. It was a tetramer with an estimated molecular weight of 230,000 daltons and an isoelectric point of 5.0. Its pH optimum of 8.5, Michaelis-Menten constant for acetaldehyde of 46 μM, and high sensitivity to noncompetitive inhibition by disulfiram resembled human liver cytosolic aldehyde dehydrogenase. Low concentrations of magnesium (5-10μM) resulted in enhancement of erythrocyte aldehyde dehydrogenase activity, whereas higher physiological concentrations of magnesium resulted in uncompetitive inhibition of enzyme activity. Magnesium inhibited the enzyme activity by increasing the binding of NADH to the enzyme as had been found to be the case for the inhibitory effect of magnesium on the human liver cytosolic enzyme. Erythrocyte aldehyde dehydrogenase may metabolize small amounts of acetaldehyde escaping the liver during ethanol metabolism and protect extrahepatic tissues from acetaldehyde toxicity.
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