Evidence of exchangeable protons in the donor groups of the acidic form of cobalt bovine carbonic anhydrase B.

T₁ relaxation measurements on water protons of solutions containing cobalt(II) bovine carbonic anhydrase have been found to be affected by the paramagnetic center. T₁ shortening has been found to be substantially pH independent. These data are diagnostic of the presence of exchangeable protons in the donor groups of the enzyme, and consistent with a water molecule in the donor set at low pH values. Previous researchers failed to reveal exchangeable protons at low pH values because of the presence of Tris-sulfate buffer which interacts with the metal ion.