Effects of pH and inhibitors on the absorption spectrum of cobalt(II)-substituted carbonic anhydrase III from bovine skeletal muscle.

Bovine apocarbonic anhydrase III has been prepared by incubation with 2-carboxy-1,10-phenanthroline at pH 5.5. The Co(II)-substituted enzyme has been prepared and its absorption spectrum has been studied. The spectrum is nearly pH-independent above pH 6. It is very similar to the high pH spectral forms of Co(II)-carbonic anhydrases I and II. The spectra of complexes with the sulfonamide inhibitor, acetazolamide, and with CN- and NCO - are virtually identical to the spectra of the corresponding complexes with Co(II)-isoenzymes I and II. The spectrum of the N-3 complex indicates that this anion is bound somewhat differently in Co(II) isoenzyme III than in the other Co(II)-substituted isoenzymes.