Direct measurement of the pK values of an alkaline Bohr group in human hemoglobin.

Proton nuclear magnetic resonance spectra of normal and des-(his 146beta) human hemoglobin in the aromatic resonance region have been compared at different pH values. From these measurements, a pK value for histidine 146beta of 7.1 in carbonmonoxyhemoglobin and 8.0 in deoxyhemoglobin has been found. These pK values confirm the proposed role of histidine 146beta in the alkaline Bohr effect.