Castor bean lipase: action on its endogenous substrate*

Abstract

A method is described for obtaining a lipase emulsion from castor beans which rapidly hydrolyzes all of its endogenous substrate at an optimum pH of 4.0 to 4.2. The course of hydrolysis can be described by a first-order reaction; no additives are required for activity and the reaction goes to completion in less than 1 hour. The enzyme emulsion (oil-in-water) is stable for at least 2 weeks in a pH 7.0 phosphate buffer containing added cysteine and ethylenediaminetetraacetic acid; it is rather heat stable, but the activity is lowered by mechanical shaking. Reagents that react with sulfhydryl groups inactivate the enzyme; the inhibition by mercuric ion and p-chloromercuribenzoic acid can be reversed with an excess of cysteine. The lipase emulsion is not inhibited by diisopropylfluorophosphate in concentrations lower than 0.01 M, nor by protamine sulfate and heparin in relatively high concentrations. It is inhibited by 0.01 M fluoride.