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Characterization of pulmonary alveolar esterases of the primate Cercopithecus pygerythrus
1Department of Pharmaceutical Chemistry, University of the Western Cape, Bellville, South Africa.
Purpose:
To evaluate and classify the hydrolases of the primate lung.
Methods:
Homologous series of aromatic, aliphatic, and choline ester substrates were assayed with the pH-stat method to obtain the Michaelis-Menten kinetic constants, Vmax and K(m), for the enzymes in pulmonary alveolar tissue with esterase activity. Polyacrylamide gel electrophoresis was employed to determine the number of such hydrolytic enzymes. Inhibition studies with selective esterase inhibitors were carried out 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 metabolized at faster rates than the other substrates. Aromatic ester hydrolysis was also inhibited by triorthocresylphosphate (TOCP), a potent inhibitor of carboxylesterases. Inhibitors of arylesterases and cholinesterases had minimal effect on the enzymic hydrolysis of all substrates. Polyacrylamide gel electrophoresis demonstrated three enzymes to have esterolytic activity, two (MWs 269 and 281 kDa) of which were sensitive to TOCP and are therefore carboxylesterases. The third enzyme (MW 34 kDa), was unaffected by esterase inhibitors and, thus, cannot be classified as an esterase.
Conclusions:
Primate pulmonary alveolar tissue contains two isozymes of carboxylesterases.