Chemical studies on rice bran lipase

Abstract

Rice bran lipase contained 16.00 +/- 0.15% nitrogen and was composed of about 320 amino acid residues. It also had a small quantity of lipid material (about 0.5%). The calculated molecular weight from SDS- polyacrylamide gel electrophoresis (and by gel filtration of Sephadex G-100) was about 40,000 +/- 2,000. Disc gel electrophoresis in the presence or absence of 8M urea and results of experiments on molecular- weight determination indicated that the enzyme had no subunits. The amino terminal of the enzyme protein was blocked by acetyl group and the carboxy-terminal residue was phenylalanine. Among the sulfhydryl- blocking reagents, only p-chloromercuribenzoate significantly inhibited the enzyme activity. Iodine, hydrogen peroxide, copper sulfate, and higher concentrations of organofluorophosphates adversely affected lipase activity. Results of the experiments on the action of N-bromosuccinimide on lipase showed that the enzyme required one or more tryptophan residues for activity.