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Angiotensin‐converting enzyme 2 catalytic activity in human plasma is masked by an endogenous inhibitor
Author(s) -
Lew Rebecca A.,
Warner Fiona J.,
Hanchapola Iresha,
Yarski Michael A.,
Manohar Jay,
Burrell Louise M.,
Smith A. Ian
Publication year - 2008
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2007.040352
Subject(s) - endogeny , chemistry , angiotensin ii , enzyme , renin–angiotensin system , medicine , endocrinology , angiotensin converting enzyme , substrate (aquarium) , divalent , cytosol , ace inhibitor , enzyme inhibitor , biochemistry , receptor , biology , blood pressure , ecology , organic chemistry
Angiotensin‐converting enzyme 2 (ACE2) is thought to act in an opposing manner to its homologue, angiotensin‐converting enzyme (ACE), by inactivating the vasoconstrictor peptide angiotensin II and generating the vasodilatory fragment, angiotensin(1–7). Both ACE and ACE2 are membrane‐bound ectoenzymes and may circulate in plasma as a consequence of a proteolytic shedding event. In this study, we show that ACE2 circulates in human plasma, but its activity is suppressed by the presence of an endogenous inhibitor. Partial purification of this inhibitor indicated that the inhibitor is small, hydrophilic and cationic, but not a divalent metal cation. These observations led us to develop a method for removal of the inhibitor, thus allowing detection of plasma ACE2 levels using a sensitive quenched fluorescent substrate‐based assay. Using this technique, ACE2 activity measured in plasma from healthy volunteers ( n = 18) ranged from 1.31 to 8.69 pmol substrate cleaved min −1 ml −1 (mean ± s.e.m ., 4.44 ± 0.56 pmol min −1 ml −1 ). Future studies of patients with cardiovascular, renal and liver disease will determine whether plasma ACE2 is elevated in parallel with increased tissue levels observed in these conditions.