title: Characterization of angiotensin converting enzyme from rat tissue by radio-inhibitor binding studies.
abstract: Angiotensin converting enzyme (ACE) derived from rat lung, aorta, epididymus, brain, kidney and plasma was characterized by radio-inhibitor (125I-MK351A) binding studies. Under optimal binding conditions at equilibrium 125I-MK351A bound to ACE was displaced from ACE in a concentration related manner by unlabelled MK351A. MK351A binding site concentration for each tissue and equilibrium dissociation constant (KD) was estimated by Scatchard analysis of binding data. Binding sites/mg protein was greatest in lung and least in brain. The KD for kidney ACE was significantly higher than that of lung, aorta, epididymus or brain ACE (P less than 0.005; t-test, d.f. = 10). 125I-MK351A bound to ACE prepared from lung and kidney was displaced in a concentration dependent manner by SQ20881, SQ14225, MK422, and Ro31-3113-000. Concentration of ACE inhibitor required to displace 50% of bound 125I-MK351A (DD50) was consistently higher for kidney-derived ACE than lung-derived ACE. The differences in radio-inhibitor binding characteristics of ACE from different rat tissues suggests that the enzyme active site may not be identical in all organs.
mesh_terms: D000806:Angiotensin-Converting Enzyme Inhibitors; D000818:Animals; D004151:Dipeptides; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism*; D011485:Protein Binding; D011869:Radioligand Assay; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D004151:Dipeptides; C042037:L-proline, N2-((1S)-1-carboxy-3-phenylpropyl)-N6-((4-hydroxyphenyl)iminomethyl)-L-lysyl-; D007703:Peptidyl-Dipeptidase A