Fatty acid selectivity of a lipase purified from Vernonia galamensis seed

Vernonia galamensis is an annual herb whose seed oil contains high levels of an epoxy fatty acid, vernolic (cis-12,13-epoxy cis-9-octadecenoic) acid. The seed also contains lipase activity in the dormant state. A lipase was purified from the seed and its substrate specificity studied in isooctane. The lipase shows pronounced selectivity for the native triacylglycerol, trivernolin. The rate of hydrolysis of triolein, the corresponding non epoxy triacylglycerol, is only 3% of that of trivernolin. In the acidolysis of tricaprylin using a mixture of fatty acids, the Vernonia lipase also showed selectivity for vernolic acid. Michaelis-Menten kinetics of the hydrolysis of triacylglycerols revealed that the observed high selectivity of the Vernonia lipase for trivernolin was mainly due to a higher V_max for trivernolin. The V_max value for the hydrolysis of trivernolin was 5 times higher than that for triolein. This novel substrate specificity is an adaptation by the seed lipase to the triacylglycerols of the seed oil that contain up to 80% vernolic acid.