Angiotensin Converting Enzyme

Synonyms

ACE

Definition

Angiotensin converting enzyme (ACE) is identical to kininase II. It is an essential component of both the renin−angiotensin system and the kallikrein−kinin system. Three different forms of ACE are known. It exists as a membrane bound protein with a molecular weight of 150–180 kD, anchored to the cytoplasmatic membrane of endothelial cells and as a circulating protein of similar size. The enzyme consists of two highly homologous lobes with an active site in each lobe. Interestingly, although still of uncertain consequence, the active sites exhibit different catalytic profiles and different affinities for ACE inhibitors. A third, smaller form of ACE (90 kD) with only one active site is expressed in mature germ cells.

The substrate specificity of ACE is low. ACE cleaves a variety of pairs of amino acids from the carboxy-terminal part of several peptide substrates. The conversion of ANG I to ANG II and the degradation of bradykinin to inactive fragments are...