title: Metal binding to angiotensin converting enzyme: implications for the metal binding site.
abstract: Angiotensin converting enzyme interacts with the chelator, 1,10-phenanthroline (OP) to form an OP-Zn-ACE ternary complex, which subsequently dissociates to OP-Zn and apoenzyme. The association and dissociation rate constants for the reaction OP + Zn-ACE in equilibrium OP-Zn-ACE have been determined and compared with those of known OP-metal complexes. Such constants were also used to calculate the rate constant for formation of the OP-Zn complex from OP-Zn-ACE. The rate of dissociation of zinc from ACE has been measured in the presence of EDTA (which acts only as a metal scavenger) as a function of chelator concentration, at different pH values, and with different buffers. The stability constant for the binding of zinc to apoACE log Kc = 8.2, determined by equilibrium dialysis using atomic absorption spectroscopy to assess metal concentration, is much smaller than that for Zn-carboxypeptidase A. Zn-thermolysin, or Zn-carbonic anhydrase. This weak binding is attributable to the zinc dissociation rate constant of ACE, 7.5 X 10(-3) sec-1 at pH 7.0, which is much greater than that of the other zinc metalloenzymes. These results lead to inferences regarding the metal binding site of ACE.
mesh_terms: D001665:Binding Sites; D002021:Buffers; D002614:Chelating Agents / Q000494:pharmacology; D055598:Chemical Phenomena; D002621:Chemistry; D004355:Drug Stability; D006207:Half-Life; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008670:Metals / Q000378:metabolism*; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism*
chemical_list: D002021:Buffers; D002614:Chelating Agents; D008670:Metals; D007703:Peptidyl-Dipeptidase A