title: The functional role of tyrosine-200 in human testis angiotensin-converting enzyme.
abstract: The active site of angiotensin-converting enzyme (ACE) has been shown by chemical modification to contain a critical tyrosine residue, identified as Tyr-200 in human testis ACE (hTACE). We have expressed a mutant hTACE containing a Tyr-200 to Phe mutation. The mutant exhibits a marked decrease in kcat: 15-fold and 7-fold for the hydrolysis of furanacryloyl-Phe-Gly-Gly and angiotensin I, respectively, whereas its Km increases by only 1.6- and 2.2-fold, respectively. We conclude that Tyr-200 is not required for substrate binding. Instead, the effect on kcat together with a 100-fold decrease in affinity for the ACE inhibitor lisinopril indicates that Tyr-200 may participate in catalysis by stabilizing the transition state complex. Thus, Tyr-200 in hTACE has a role analogous to that of Tyr-198 in carboxypeptidase A.
authors.affiliation: Center for Biochemical and Biophysical Sciences and Medicine, Harvard Medical School, Boston, MA 02115.
authors.forename: Y N
authors.initials: YN
authors.lastname: Chen
authors.forename: M R
authors.initials: MR
authors.lastname: Ehlers
authors.forename: J F
authors.initials: JF
authors.lastname: Riordan
mesh_terms: D000595:Amino Acid Sequence; D000803:Angiotensin I / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D006801:Humans; D007700:Kinetics; D008297:Male; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D009842:Oligopeptides; D007703:Peptidyl-Dipeptidase A / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010957:Plasmids; D013379:Substrate Specificity; D013737:Testis / Q000201:enzymology*; D014162:Transfection; D014443:Tyrosine
chemical_list: D009842:Oligopeptides; D014443:Tyrosine; D000803:Angiotensin I; D007703:Peptidyl-Dipeptidase A