Inhibition of Bohr effect after removal of C-terminal histidines from haemoglobin beta-chains.

Abstract

THE alkaline Bohr effect is the uptake of protons at a pH greater than 6 when oxygen is removed from haemoglobin1. In horse haemoglobin the α-amino groups of the α-chain contribute about one-quarter of the alkaline Bohr effect2. Recently Perutz et al.3 proposed that histidine 146β contributes about half the alkaline Bohr effect. Their evidence was based on the interpretation of a difference Fourier map of deoxyhaemoglobin after reaction with N-ethylmaleimide4. This haemoglobin has lost half its alkaline Bohr effect. We have prepared des-(His 146β) human haemoglobin: it exhibits haem-haem interaction and lacks half the alkaline Bohr effect, and thus fully confirms the ideas of Perutz et al.3.