title: Angiotensin converting enzyme (ACE), characterization by 125I-MK351A binding studies of plasma and tissue ACE during variation of salt status in the rat.
abstract: Angiotensin converting enzyme (ACE) was measured in rat plasma and tissues by analysis of the binding of the radio-inhibitor 125I-MK351A, a tyrosyl derivative of enalaprilic acid. Labelled 125I-MK351A bound to plasma and tissue ACE preparations and was displaced in a concentration-related manner by MK351A. Scatchard analysis yielded a single line from which MK351A binding sites/mg protein and MK351A dissociation constant were calculated. Tissue and plasma ACE from Sprague Dawley rats was studied over a wide range of sodium intakes (low salt, 0.026 +/- 0.012 mmol/24 h; normal salt, 0.58 +/- 0.09 mmol/24 h; and high salt, 10.4 +/- 1.3 mmol/24 h) and during high salt and DOCA treatment. Across the range of sodium states studied there were no consistent changes in plasma, lung, aorta, brain, epididymis or kidney MK351A binding sites/mg protein, or equilibrium dissociation constant. Calculated MK351A binding sites (nmol/mg protein) were 1.64 +/- 0.14 in lung, 0.47 +/- 0.04 in aorta, 0.44 +/- 0.05 in epididymis, 0.18 +/- 0.01 in brain and 0.053 +/- 0.004 in kidney preparations (n = 24 in each group) reflecting reported ACE enzymatic activity in these tissues. Equilibrium dissociation constant KD was uniform within each tissue, but varied between organs. The KD (mol/l X 10(-12)) was 50 +/- 2 in aorta, 57 +/- 2 in lung, 58 +/- 2 in epididymis, 61 +/- 3 in brain, 62 +/- 2 in plasma and 84 +/- 3 in kidney (n = 24 in each group).(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000804:Angiotensin II / Q000097:blood; D000806:Angiotensin-Converting Enzyme Inhibitors; D000818:Animals; D001011:Aorta / Q000201:enzymology; D001665:Binding Sites; D001921:Brain / Q000201:enzymology; D004151:Dipeptides / Q000378:metabolism*; D004822:Epididymis / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000201:enzymology; D008168:Lung / Q000201:enzymology; D008297:Male; D007703:Peptidyl-Dipeptidase A / Q000097:blood / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012083:Renin / Q000097:blood; D012965:Sodium Chloride / Q000008:administration & dosage*
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D004151:Dipeptides; C042037:L-proline, N2-((1S)-1-carboxy-3-phenylpropyl)-N6-((4-hydroxyphenyl)iminomethyl)-L-lysyl-; D000804:Angiotensin II; D012965:Sodium Chloride; D007703:Peptidyl-Dipeptidase A; D012083:Renin