Interaction of acetazolamide and 4-nitrothiophenolate ion with bivalent metal ion derivatives of bovine carbonic anhydrase.

The stability and rate constants for the interaction of acetazolamide (diamox) and 4-nitrothiophenolate ion (NTP) with the bivalent Mn, Co, Ni, Cu and Cd forms of bovine carbonic anhydrase have been measured by utilizing the distinct visible spectra of each metalloenzyme-NTP adduct. Differing stabilities of the various NTP and (particularly) diamox complexes reside mainly in varying values for the dissociation rate constants (kd). Intrinsic formation rate constants (for the acid form of the enzyme reacting with the basic form of the ligand) are uniformly high (greater than or equal 2 X 10(7) M-1 s-1 at 25 degrees C). Invariance of kd with pH and a bell-shaped log K-pH profile with the Cu-enzyme adducts are features observed previously with the native enzyme. Binding of NTP with the Cu and Cd metalloenzymes is stronger than to the native form.