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X-ray Studies of the Interaction of CO2 with Human Deoxyhaemoglobin


IN addition to transporting CO2 indirectly by way of the alkaline Bohr effect, haemoglobin can interact directly with CO2 to form carbamate residues : RNH2 + CO2RNHCOO + 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).

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