CONVERSION OF ANGIOTENSIN-I TO ANGIOTENSIN-II BY CHYMASE ACTIVITY IN HUMAN PULMONARY MEMBRANES

An aprotinin-insensitive, angiotensin II (Ang II)-forming chymase has recently been identified in human heart tissue. We studied the hydroly sis of Ang I in human lung membranes. The hydrolysis products Ang II, Ang III, Ang-(1-9), Ang-(2-9), Ang-(1-7) and Ang-(8-10) appeared in me mbrane preparations from four patients. Two metabolic pathways for the formation of Ang LI were identified; one depending on ACE activity (1 .4 nmol Ang 11/min/mg membrane protein) and the other on serine protea se activity (2.1 nmol/min/mg). The serine protease activity was inhibi table to only 30 +/- 8% (mean +/- SEM) by aprotinin, suggesting chymas e activity to play a role in the Ang I-conversion of human lung. (C) 1 997 Elsevier Science Inc.