IN addition to transporting CO2 indirectly by way of the alkaline Bohr effect, haemoglobin can interact directly with CO2 to form carbamate residues : RNH2 + CO2⇌RNHCOO− + H+ This reaction of CO2 with haemoglobin is oxygen-linked so that at constant pH more CO2 is bound to deoxy- than to oxyhaemoglobin, and conversely the oxygen affinity of haemoglobin is decreased in the presence of CO2 (refs 1 and 2). The studies of Kilmartin and Rossi-Bernardi3,4 on horse haemoglobin specifically modified at the N terminal amino groups by reaction with cyanate showed that at constant pH CO2 has no effect on the oxygen affinity of haemoglobin when all four α-amino groups are carbamylated, but that only part of the oxygen-linked effect is inhibited when the α-amino groups of only the α or only the β chains are blocked. This implies that the N-terminal amino groups are solely responsible for the oxygen-linked CO2 interactions and that this effect is shared between the α and β chains. More recent experiments have confirmed these results for human haemoglobin5.
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ARNONE, A. X-ray Studies of the Interaction of CO2 with Human Deoxyhaemoglobin. Nature 247, 143–145 (1974). https://doi.org/10.1038/247143a0
Pfl�gers Archiv European Journal of Physiology (1979)
Effects of inositol hexaphosphate on the Bohr effect induced by CO2 and fixed acids in chicken hemoglobin
Pfl�gers Archiv European Journal of Physiology (1978)