ENZYMATIC PATHWAY TO ETHYL VINYL KETONE AND 2-PENTENAL IN SOYBEAN PREPARATIONS

Previous work. by this laboratory showed that under anaerobic conditio ns and the presence of a polyunsaturated fatty acid, soybean (Glycine max L.) lipoxygenase isoenzymes converted a lipoxygenase-catalyzed oxi dation product of Linolenic acid, 3(S)-hydroperoxy-9(Z),11(E),15(Z)-oc tadecatrienoic acid, into 1-penten-3-ol, 2(Z)-penten-1-ol, and 13-oxo- 9(Z),11(E)-tridecadienoic acid. It seemed plausible that the ''raw bea n odor'', ethyl vinyl ketone, previously isolated from soybean homogen ates by other workers could arise from oxidation of 1-penten-3-ol by a lcohol dehydrogenase. It is shown here that both ethyl vinyl ketone an d 2-pentenal are produced by a soybean preparation after anaerobic inc ubation with 3(S)-hydroperoxy-9(Z),11(E),15(Z)-octadecatrienoic acid a nd linolenic acid and that NAD(+) stimulated the formation of 2-penten al. In the presence of NAD+, two separable isoenzymes of soybean alcoh ol dehydrogenase were capable of utilizing as substrates both 1-penten -3-ol and 2(Z)-penten-1-ol, as well as (2E)-hexen-1-ol. In terms of su bstrate preference indicated by K-m, the order was 2(E)-hexen-1-ol > 2 (Z)-penten-1-ol > 1-penten 3-ol. Because ethyl vinyl ketone formed in the presence of only 3(S)-hydroperoxy-9(Z),11(E),15(Z)-octadecatrienoi c acid and linolenic acid in the absence of NAD(+), another pathway al so seemed possible.