Lipase in the Lipid Bodies of Corn Scutella during Seedling Growth

Abstract

In the scutella of corn (Zea mays), lipase activity is absent in ungerminated seeds and increases during seedling growth. At the peak stage of lipolysis, about 50% of the lipase activity is recovered in the lipid body fraction after flotation centrifugation. The lipase is tightly bound to the lipid bodies, and resists solubilization by repeated washing with buffers or NaCl solutions. Isolated lipid bodies undergo autolysis of internal triacylglycerols, resulting in the release of fatty acids. After the triacylglycerols in isolated lipid bodies have been extracted with diethyl ether, the lipase is recovered in the membrane fraction. The lipase has an optimal activity at pH 7.5 in the autolysis of lipid bodies, or on trilinolein or N-methylindoxylmyristate. Of the various acylglycerols examined, the enzyme is active only on acylglycerols of linoleic and oleic acids which are the major fatty acid constituents of corn oil. The activity is not greatly affected by NaCl, CaCl(2), or pretreatment of the enzyme with p-chloromercuribenzoate or mersalyl, and detergents abolish the activity. The enzyme hydrolyzes trilinolein completely to fatty acids; during the course of reaction, there is little accumulation of di- or mono-linolein.