THE unloading of oxygen in the tissues is facilitated by lowering the oxygen affinity of haemoglobin (Hb) by both CO2 and diphosphoglycerate (DPG)1. This occurs because CO2 and DPG are oxygen-linked, that is, they are bound more firmly to deoxyhaemoglobin than to oxyhaemoglobin2,3. The binding of CO2 to Hb takes place by a reaction of CO2 with the α-amino groups to form carbamino compounds4,5, and binding curves can be measured by rather laborious methods4,6. Perrella et al.7 have modified these methods so that much smaller amounts of Hb, such as the specifically carbamylated Hbs8, can be used. In this method, Hb equilibrated with CO2 is rapidly taken to pH 11 to stabilise the carbamino CO2 and BioRad AG 1×8 resin added to remove carbonate and bicarbonate ions. The carbamino CO2 is displaced from the Hb by acidification and measured in a Van Slyke apparatus. DPG-free human deoxyhaemoglobin gave diphasic CO2 binding curves7 showing that the affinities of the α and β chain α-amino groups for CO2 are different, but it was impossible to establish which group had the higher affinity.
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Pfl�gers Archiv European Journal of Physiology (1979)