Pancreatic juice cholesterol esterase: Studies on molecular weight and bile salt-induced polymerization

Abstract

The molecular weight of pancreatic juice cholesterol esterase (sterol ester hydrolase, EC 3.1.1.13) has been determined to be 65–69,000 by Sephadex G-200 gelfiltration chromatography and sodium dodecylsulfate-polyacrylamide disc-gel electrophoresis. The amino acid composition resembles that of classical pancreatic lipase (EC 3.1.1.3) but is unique in the virtual absence of tyrosine in the molecule. Evidence for a direct molecular interaction between specific bile salts, i.e., cholic acid or its conjugates, and the pancreatic juice enzyme was obtained by Sephadex G-50 filtration studies. This interaction results in a polymerization of the enzyme protein to give an apparent molecular weight of approximately 400,000 as determined by standardized gel-filtration chromatography. Studies with phenylmethanesulfonylfluoride, a serine hydroxyl group reagent, indicate that the polymerized protein is the active enzyme involved in the reversible synthesis and hydrolysis of sterol esters.