Impact of angiotensin converting enzyme substrate conformation on fractional hydrolysis in the lung. Merker, Marilyn P., Ian M. Armitage, Said H. Audi, Lazaros T. Kakalis, John H. Linehan, Jeffrey R. Maehl, David L. Roerig, and Christopher A. Dawson. Departments of Anesthesiology, Physiology and Pharmacology\Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, Department of Veterans Affairs, Zablocki V.A. Medical Center, Milwaukee, Wisconsin 53295, Biomedical Engineering Department, Marquette University, Milwaukee, Wisconsin 53233, Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520
APStracts 2:0145L, 1995.
We examined the hydrolysis kinetics of benzoyl-phenylalanyl-glycyl -proline (BPGP) in the isolated perfused lung and in vitro for evidence of preferential hydrolysis of the trans isomer by angiotensin converting enzyme (ACE). Nuclear magnetic resonance spectroscopy (NMR) showed that BPGP exists as cis and trans isomers in a ratio of 44:56. After a single pass through the perfused rabbit lung over a wide range of infused BPGP concentrations, 42% of the BPGP was not hydrolyzed. In single pass bolus injection studies, 41% of the injected BPGP was not hydrolyzed, and very little further hydrolysis occurred in a second passage of the bolus through the lungs. In rat lung recirculation and in vitro studies of BPGP hydrolysis by ACE, 60% of the substrate was hydrolyzed rapidly compared with the remaining 40%, and the peptidyl-prolyl cis-trans isomerase, cyclophilin, increased the rate of the slower phase of the reaction in both kinds of experiments. We conclude that the rapid hydrolysis phase represents primarily the hydrolysis rate of the trans isomer and the slower phase the cis-trans isomerization rate, suggesting that the trans isomer of BPGP is preferentially hydrolyzed by ACE in the perfused lung and in vitro. 

Received 25 May 1995; accepted in final form 15 August 1995.
APS Manuscript Number L168-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 August 1995.