Metabolism of trans, trans-muconaldehyde, a microsomal hematotoxic metabolite of benzene, by purified yeast aldehyde dehydrogenase and a mouse liver soluble fraction.

Aldehyde dehydrogenase (ALDH) from yeast, in the presence of NAD+, oxidizes trans, trans-muconaldehyde (MUC) in a biphasic manner with apparent Km values of 0.48 and 3.2 microM and corresponding Vmax values of 604 and 1227 nmol/min/mg protein. Concentrations above 10 microM trans,trans-muconaldehyde produce an inhibition of enzyme activity. Removal of NAD+, MUC, or use of boiled enzyme results in no oxidation. Using thin-layer chromatography and high-pressure liquid chromatography techniques, a product with polarity intermediate between that of the dialdehyde trans,trans-muconaldehyde and the diacid trans,trans-muconic acid (MA) was detected in the ALDH incubation mixtures. The same product was also detected in a DBA/2J mouse liver soluble fraction supplemented with NAD+ and incubated with MUC. This product was isolated from a scaled-up incubation mixture containing trans,trans-muconaldehyde, purified yeast aldehyde dehydrogenase, and NAD+. Mass spectral analysis of the compound indicates a molecular weight of 126 and an empirical formula C6H6O3 containing four double bonds. This product also tested positive with reagents specific for carboxylic and aldehydic functional groups. In the presence of the mouse liver soluble fraction supplemented with NAD+, this intermediate was metabolized to MA. These findings indicate that MUC is oxidized by yeast aldehyde dehydrogenase to the monocarboxylic acid derivative which is an intermediate in the conversion of MUC to MA. The role of the monocarboxylic acid alpha,beta-unsaturated aldehyde in benzene hematotoxicity remains to be explored.