The metabolism of acetaldehyde in mammalian tissues. Reactions in rat-liver suspensions under anaerobic conditions

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Abstract
A technique has been devised which permits the rapid (2-4 seconds) and accurate removal and deproteinization of samples of tissue suspensions under anaerobic conditions. Under anaerobic conditions acetaldehyde is transformed rapidly into ethanol and acetate in suspensions of rat liver in a potassium chloride-phosphate solution. Addition of diphosphopyridine nucleotide accelerates the processes. That part of the aldehyde disappearance which is not caused by ethanol formation (the "aldehyde activity") approaches a maximum value at a diphosphopyridine nucleotide concentration of about 200 [mu][image]. The "aldehyde activity" is independent of the acetaldehyde concentration in the range examined (0.1-0.6 m[image]). The whole of the aldehyde removal is accounted for by formation of ethanol and acetate. Condensation reactions such as acetoin synthesis did not take place at the low aldehyde concentrations employed. It is concluded that during ethanol metabolism in the living organism condensation reactions of acetaldehyde can be of no quantitative importance. Addition of pyruvate or other keto acids reduced the ethanol formation to a negligible value. It is therefore concluded that rat liver does not contain any true aldehyde mutase. The ethanol formation is frequently larger than the aldehyde dehydrogenation. Evidence is obtained that this is due to reduced diphosphopyridine nucleotide, formed at a considerable rate from substrates present in the liver. The concentration of diphosphopyridine nucleotide and reduced diphophopyridine nucleotide during aldehyde metabolism was followed and the significance of the results is discussed. Addition of pyruvate increased the rate of aldehyde dehydrogenation by about 50%. It is suggested that this result may be caused by the formation of a complex between aldehyde dehydrogenase, lactic dehydrogenase and reduced diphosphopyridine nucleotide, which could be oxidized by pyruvate. The dissociation of reduced diphosphopyridine nucleotide from the aldehyde dehydrogenase, which is presumably the rate-limiting step, would in this way be circumvented.