Effects of chemical modification of amino acid residues on the activities of lipase from Candida cylindracea

Abstract

Lipase of Candida cylindracea, purified from a commercial enzyme preparation by gel filtration, was a single peptide of molecular weight about 50 000 daltons. The enzyme was subjected to chemical modification, and the activities of the modified enzyme, hydrolysis, esterification, and ester exchange, were examined. The reactions of esterification and ester exchange were carried out in organic solvent systems. When arginine residues were modified with phenylglyoxal, the enzyme lost all the activities mentioned above. Modification of aspartic acid and/or glutamic acid with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide also resulted in significant decreases in three activities of the enzyme. Inactivation was not observed on the modification of other amino acid residues examined. These results suggested that arginine residues and carboxyl groups might be involved in the catalytic site or substrate-binding site of this enzyme. In the meantime, the esterification activity was markedly enhanced by the modification of lysine residues with pyridoxal 5′-phosphate or by the reduction of disulfide bonds with dithiothreitol without appreciable loss of the hydrolysis activity.