Reactivity differences between haemoglobins. Ppart XVII. The variability of the Bohr effect between species and the effect of 2,3-diphosphoglyceric acid on the Bohr effect
The magnitude of the Bohr effect, as measured by the number of moles of hydrogen ion produced per mole of oxygen reacting with haemoglobin, Δh+, has been measured as a function of pH for five vertebrate haemoglobins. In the absence of 2,3-diphosphoglyceric acid (DPG) the alkaline Bohr effect is the same for the mammalian haemoglobins and slightly lower for pigeon haemoglobin. However the acid Bohr effect varies by a factor of 5·5 over the various haemoglobins and there is a correlation between the characteristic pH, pHch, of a haemoglobin and the magnitude of its acid Bohr effect, which implies that there is a correlation between the content of charged amino-acids in a haemoglobin and its acid Bohr effect. In the presence of DPG the alkaline Bohr effect for the mammalian haemoglobins is approximately the same and is 50–60% greater than in the absence of DPG. It is concluded that the variable magnitude of the alkaline Bohr effect measured on haemolystates from which DPG has not been removed arises from the variable affinity of different haemoglobins for DPG.