Stereospecific Hydration of cis- and trans-9,10-Epoxyoctadecanoic Acids

A soluble (105,000 x g supernatant) enzyme preparation from a pseudomonad which catalyzes the stereospecific hydration of the double bond of a number of cis-Δ9-olefinic fatty acids has been shown to catalyze the stereospecific conversion of cis- and trans-9,10-epoxystearic acids to threo- and erythro-9,10-dihydroxystearic acids, respectively. In both cases only one isomer of each of the incubated racemic substrates was utilized by the enzyme and only one isomer of each of the threo- or erythro-9,10-dihydroxystearates was formed. The results of incubations of the cis- and trans-9,10-epoxystearic acids in water enriched with respect to 18O indicated that the enzyme-catalyzed hydration of the epoxide functions occurred with stereospecific incorporation of the oxygen of water at carbon atom 10. The bacterial enzyme also catalyzed the conversion of cis-9,10-epoxypalmitic acid to 9,10-dihydroxypalmitic acid.