Human hemoglobin was reacted with potassium cyanate and purified to yield three species, α2(c)β2(c), α2(c)β2, and α2β2(c), where (c) denotes specific reaction of cyanate with the α amino group of the particular chain. The effect of carbon dioxide on the oxygen affinity of these species in the presence and in the absence of 2,3 diphosphoglycerate was measured. Carbon dioxide has no effect on the oxygen affinity of α2(c)β2(c), confirming that the usual lowering of the oxygen affinity of carbon dioxide in normal hemoglobin is mediated by the α amino groups of the α and β chains. The lowering of the oxygen affinity of α2β2(c) by carbon dioxide was not affected by the presence or absence of 2,3 diphosphoglycerate, showing that 2,3 diphosphoglycerate does not interfere with the oxygen linked binding of carbon dioxide at the α chain α amino group. In α2(c)β2 there was a much larger effect of carbon dioxide on the oxygen affinity in the absence of 2,3 diphosphoglycerate than in α2β2(c); however, on addition of 2,3 diphosphoglycerate the effect of carbon dioxide on the oxygen affinity of α2(c)β2 was much smaller and similar to that occurring in α2β2(c). This shows that there is a large difference in the carbon dioxide binding constants of the β chain α amino group in the oxy and deoxy forms of human hemoglobin, and that 2,3 diphosphoglycerate suppresses this difference, probably by binding strongly to the β chain α amino group of deoxyhemoglobin and displacing any bound carbon dioxide.
|Number of pages||5|
|Journal||Journal of Biological Chemistry|
|Publication status||Published - 1973|
ASJC Scopus subject areas