Activation and inhibition of bovine carbonic anhydrase III by dianions.
We have found that many dianionic species, at millimolar concentrations, significantly activate or inhibit the bovine carbonic anhydrase III-catalyzed hydration of CO2. Dianionic species such as HPO2-4 and SO2-3, with pKb values near 7, are activators, whereas weakly basis species such as SO2-4 act as inhibitors. Both activation and inhibition are partial hyperbolic in nature and do not appear to compete with monoanionic linear inhibitors like N-3. Our kinetic data are consistent with a formal mechanism of action for carbonic anhydrase III that is directly analogous to that of carbonic anhydrase II, in which Lys-64 of carbonic anhydrase III can act as an intramolecular H+ transfer group during CO2 hydration. Our data suggest that dianionic inhibitors depress the rate of H+ transfer during turnover by stabilizing the protonated form of Lys-64. We postulate that dianionic activators enhance the rate of a rate-limiting H+ transfer step in the mechanism, probably by acting directly as H+ acceptors.
Rowlett
R S
RS
Department of Chemistry, Colgate University, Hamilton, New York 13346.
Gargiulo
N J
NJ
Santoli
F A
FA
Jackson
J M
JM
Corbett
A H
AH
D000818:Animals; D000838:Anions; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology*; D002256:Carbonic Anhydrases / Q000378:metabolism*; D002384:Catalysis; D002417:Cattle; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D010710:Phosphates; D013431:Sulfates
D000838:Anions; D002257:Carbonic Anhydrase Inhibitors; D010710:Phosphates; D013431:Sulfates; D002256:Carbonic Anhydrases