Carboxylesterase aus Rinderlebermikrosomen, I. Isolierung, Eigenschaften und Substratspezifität

Abstract

A carboxylesterase (EC 3.1.1.1) of beef liver microsomes was isolated and characterized. The enzyme was purified about 70-fold (based on the specific activity of the microsomes) in 20% yield. The preparation was homogeneous in column chromatography, gel-filtration and paper electrophoresis. In high voltage electrophoresis on starch gel, an additional faster-moving esterase-active band was detected. The enzyme hydrolyzes a series of carboxyl esters and aromatic acid amides, but the substrate specificity showed some differences from that of the carboxylesterases from the liver and kidney of the pig, which we described previously. Besides the hydrolysis into acid and alcohol, the enzyme also catalyzes the transfer of amino acid residues to form dipeptides, e.g. L-phenylalanyl-L-phenylalanine from L-phenylalanine-methyl ester, and L-tyrosyl-L-tyrosine from L-tyrosine-ethyl ester. The enzyme is very potently inhibited by organophosphate inhibitors (E 600, phosphoric acid-bis-[p-nitrophenyl ester]).