Vibrio harveyi aldehyde dehydrogenase. Partial reversal of aldehyde oxidation and its possible role in the reduction of fatty acids for the bioluminescence reaction

Vibrio harveyi aldehyde dehydrogenase, which catalyzes the oxidation of long chain aliphatic aldehydes to acids, has been discovered to have both acyl-CoA reductase and thioesterase activities. Tetradecanoyl-CoA was reduced to tetradecanal in the presence of NAD(P)H, as monitored by the stimulation of luciferase activity by the aldehyde product (acyl-CoA reductase). In the absence of NADPH, [³H]tetradecanoyl-CoA was hydrolyzed to the hexane-soluble fatty acid (thioesterase). Inhibition data with N-ethylmaleimide suggest that a single active site on aldehyde dehydrogenase is responsible for all three enzymatic activities. The acyl-CoA reductase activity was maximal at low NADPH concentration (about 1 μM), whereas much higher concentrations of NADH (>100-fold) were required for optimal activity. Further increases in NADPH or NADH concentrations inhibited both the acyl-CoA reductase and thioesterase reactions. On the basis of the specificity of aldehyde dehydrogenase for NADP(H), an improved purification procedure employing affinity chromatography on 2',5'-ADP-Sepharose is described. Although fatty acid reductase activity could not be reconstituted, aldehyde dehydrogenase specifically stimulated the rate of acylation of the acyl protein synthetase component from the Photobacterium phosphoreum fatty acid reductase system. This observation, combined with the partial reversal of aldehyde oxidation described above, suggests a possible role for aldehyde dehydrogenase in aldehyde biosynthesis for the luminescent reaction in V. harveyi.