Studies on avian erythrocyte metabolism: Effect of organic phosphates on oxygen affinity of embryonic and adult-type hemoglobins of the chick embryo

Abstract

The effects of 2,3 diphosphoglyceric acid (2,3-DPG), adenosine triphosphate (ATP), and inositol hexaphosphate (IHP) on the oxygen affinity of whole “stripped” hemoglobin (WSH), hemoglobin H (Hb-H), hemoglobin A (Hb-A) and hemoglobin D (Hb-D) isolated from 18-day chick embryo blood have been determined. The effect of the three organic phosphates upon the oxygen dissociation curves is similar and the following order of decreasing oxygen affinity of the organic phosphates was observed for each hemoglobin: 2,3-DPG < ATP < IHP. 2,3-DPG appears to have a slightly greater effect upon the P 50 of Hb-H than upon that of either of the two adult-type hemoglobins. However, this effect seems insufficient to suggest a preferential interaction of 2,3-DPG with Hb-H which would account for either the large amounts of 2,3-DPG in the erythrocytes of embryos or the higher oxygen affinity of the whole blood. The effects of the organic phosphates upon the Hill constant of the purified hemoglobins are variable. It is concluded that since the distribution of hemoglobins H, A, and D in the erythrocytes during the developmental period from 18-day embryos to 6-day chicks remains fairly constant, the previously described progressive decrease in oxygen affinity of the whole blood during this period results from changes in the total amount and distribution of the intraerythrocytic organic phosphates. 2 2 Abbreviations used: 2,3-DPG, 2,3-diphosphoglyceric acid; IHP, inositol hexaphosphate; IPP, inositol pentaphosphate; Hb-A, major hemoglobin of adult chicken; Hb-D, minor hemoglobin of adult chicken; Hb-H, embryonic or hatching chick hemoglobin; WSH, whole stripped hemoglobin; P 50, pO 2, in millimeters of Hg, required to produce 50% saturation.