CHARACTERIZATION OF PULMONARY ALVEOLAR ESTERASES OF THE PRIMATE CERCOPITHECUS-PYGERYTHRUS

Purpose. To evaluate and classify the hydrolases of the primate lung. Methods. Homologous series of aromatic, aliphatic, and choline ester s ubstrates were assayed with the pH-stat method to obtain the Michaelis -Menten kinetic constants, V-max and K-m, for the enzymes in pulmonary alveolar tissue with esterase activity. Polyacrylamide gel electropho re sis was employed to determine the number of such hydrolytic enzymes . Inhibition studies with selective esterase inhibitors were carried o ut to classify enzymes as either arylesterases, carboxylesterases, or cholinesterases. Results. Aromatic, aliphatic, and choline ester drugs were hydrolyzed by alveolar tissue of the primate lung. The catalytic enzymes were more specific for aromatic esters since these were metab olized at faster rates than the other substrates. Aromatic ester hydro lysis was also inhibited by triorthocresylphosphate (TOCP), a potent i nhibitor of carboxylesterases. inhibitors of arylesterases and choline sterases had minimal effect on the enzymic hydrolysis of all substrate s. Polyacrylamide gel electrophoresis demonstrated three enzymes to ha ve esterolytic activity, two (MWs 269 and 281 kDa) of which were sensi tive to TOCP and are therefore carboxylesterases. The third enzyme (MW 34 kDa), was unaffected by esterase inhibitors and, thus, cannot be c lassified as an esterase. Conclusions, Primate pulmonary alveolar tiss ue contains two isozymes of carboxylesterases.