The acid lipase of the castor bean. Properties and substrate specificity*

Abstract

A castor bean lipase with a pH optimum of 4.3 is found within the fatty layer obtained by centrifuging a homogenate of the bean; most of the fat may be removed by extraction with ethyl ether in the presence of saturated sodium chloride solution, yielding a preparation which consists of about 55% protein and 5% lipid and which is insoluble in neutral buffer. This preparation emulsifies triglycerides and hydrolyzes them completely; the enzyme is inhibited by mercurials but not by diisopropylfluorophosphate. The data on effect of enzyme concentration on hydrolysis rate suggest that a second component, perhaps an emulsifier, is required for activity. Hydrolysis of triglycerides of saturated fatty acids is maximum at a chain length between C4 and C8. Triacetin is not hydrolyzed. Glycerides of long-chain fatty acids, predominantly unsaturated C18, are also hydrolyzed, but not as rapidly as the maximum for the glycerides of short-chain fatty acids. Mono- and dibutyrin are hydrolyzed less rapidly than tributyrin, but diolein is hydrolyzed more rapidly than triolein; this suggests that there may be two separate enzymes for the short-chain and long-chain triglycerides, respectively. Esters of ricinoleic acid and monohydric alcohols are hydrolyzed at a much lower rate than is castor oil.