title: Kinetic probes for inter-domain co-operation in human somatic angiotensin-converting enzyme.
abstract: s-ACE (the somatic form of angiotensin-converting enzyme) consists of two homologous domains (N- and C-domains), each bearing a catalytic site. Negative co-operativity between the two domains has been demonstrated for cow and pig ACEs. However, for the human enzyme there are conflicting reports in the literature: some suggest possible negative co-operativity between the domains, whereas others indicate independent functions of the domains within s-ACE. We demonstrate here that a 1:1 stoichiometry for the binding of the common ACE inhibitors, captopril and lisinopril, to human s-ACE is enough to abolish enzymatic activity towards FA {N-[3-(2-furyl)acryloyl]}-Phe-GlyGly, Cbz (benzyloxycarbonyl)-Phe-His-Leu or Hip (N-benzoylglycyl)-His-Leu. The kinetic parameters for the hydrolysis of seven tripeptide substrates by human s-ACE appeared to represent average values for parameters obtained for the individual N- and C-domains. Kinetic analysis of the simultaneous hydrolysis of two substrates, Hip-His-Leu (S1) and Cbz-Phe-His-Leu (S2), with a common product (His-Leu) by s-ACE at different values for the ratio of the initial concentrations of these substrates (i.e. sigma=[S2]0/[S1]0) demonstrated competition of these substrates for binding to the s-ACE molecule, i.e. binding of a substrate at one active site makes the other site unavailable for either the same or a different substrate. Thus the two domains within human s-ACE exhibit strong negative co-operativity upon binding of common inhibitors and in the hydrolysis reactions of tripeptide substrates.
authors: Chemistry Faculty, Lomonosov Moscow State University, Moscow 119992, Russia.
authors: Olga E
authors: OE
authors: Skirgello
authors: Peter V
authors: PV
authors: Binevski
authors: Vladimir F
authors: VF
authors: Pozdnev
authors: Olga A
authors: OA
authors: Kost
mesh_terms: D000806:Angiotensin-Converting Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002216:Captopril / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D017706:Lisinopril / Q000737:chemistry / Q000378:metabolism; D007703:Peptidyl-Dipeptidase A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D002216:Captopril; D017706:Lisinopril; D007703:Peptidyl-Dipeptidase A