Partial purification and properties of a cis-3: trans-2-enal isomerase from cucumber fruit

An enzyme, which catalyses the isomerisation of cis-3-enals to trans-2-enals, has been partially purified from cucumber fruit. The isomerase activity has been resolved from significant contamination by the related activities, lipoxygenase and hydroperoxide cleavage enzymes. An examination of the substrate specificity of the isomerase enzyme showed it to be specific for the cis-3-enals. The most efficient isomerisation was achieved with cis-3-hexenal and cis-3-nonenal which are, physiologically, the two most significant substrates. The trans-3-enal and cis-3-enol were not suitable substrates for the enzyme.