The positional and fatty acid selectivity of oat seed lipase in aqueous emulsions

The positional and fatty acid selectivities of oat (Avena sativa L.) seed lipase (triacylglycerol hydrolase EC 3.1.1.3) were examined. Pure triacylglycerols were used as substrates. The products of lipolysis were examined by thin-layer chromatography and gas-liquid chromatography. Only symmetrical triacylglycerols were used as substrates; thus potential complications arising from stereobias were avoided. Controls were carried out with a lipase specific for primary positions. The lipase from oat seeds catalyzed the hydrolysis of both primary and secondary esters. When the lipase was tested upon mixtures of homoacid triacylglycerols (triacylglycerols composed of the same three fatty acids), the lipase acted most rapidly upon those containing oleate, elaidate, linoleate and linolenate. Strong intermolecular selectivity against homoacid triacylglycerols containing palmitate, petroselinate and stearate was observed. Comparison of assays performed at 26°C with those performed at 45°C showed that selectivity was temperature-independent. When mixed-acid triacylglycerols containing both oleate and stearate were treated with lipase, intramolecular selectivity was observed, with oleate hydrolysis predominating. From this work and earlier work, it can be concluded that the selectivity exhibited by the oat seed lipase is similar to that of the lipase fromGeotrichum candidum, except that the oat seed lipase attacks elaidate, a fatty acyl group with atrans double bond, whereas theG. candidum lipase strongly discriminates against elaidate.