Peptide inhibitors and the active site(s) of angiotensin converting enzyme

Angiotensin converting enzyme (ACE) is a central participant in blood pressure regulation and is strategically located within the pulmonary vasculature in order to carry out this function. It is also present in kidney, brain and a variety of other tissues where its function is unknown. The molecular weight of ACE from these sources is approximately 185,000. A smaller form of the enzyme, Mr approximately 100,000, is found in mature testis; its function is also unknown. The lung form of human ACE contains 1277 amino acids and consists of two homologous repeated domains, each of which appears to have a potential catalytic site. The testis form of human ACE contains 701 amino acids and has only a single domain which is largely identical to the carboxy-terminal half of the lung enzyme. This raises important questions such as, why does lung ACE possess two possible active sites, do each of the two bind zinc, and are they both catalytically active? To answer these questions, we have examined the binding of potent peptide inhibitors to ACE, redetermined the zinc stoichiometry and chemically modified both lung and testicular ACE with fluorodinitrobenzene (FDNB). Peptide inhibitors bind with essentially a 1:1 stoichiometry, indicative of a single active site. The zinc content of lung ACE is 1.4-1.8 g-at/mol. For testicular ACE it is 0.8-1.1 g-at/mol. FDNB modifies a single tyrosine, and to a much lesser extent a lysine, with concomitant loss of all catalytic activity. Sequence analysis identifies the specific residues modified and indicates that they occur only in the carboxy terminal half of lung ACE.(ABSTRACT TRUNCATED AT 250 WORDS)