Studies on Avian Erythrocyte Metabolism

The erythrocyte count of the adult ostrich (∼ 2.0 × 10 6 /mm 3 ) is about 40% of that of man (∼ 5.0 × 10 6 /mm 3 ) but the red blood cell is approximately three times larger (220 μm 3 ). The total phosphate content per cm 3 red blood cell is 37.7 μmol. Inositol tetrakisphosphate (inositol‐ P 4 ), a compound not previously reported in the erythrocytes of any species of animal, is the major organic phosphate in erythrocytes of the adult ostrich, accounting for 35 % of the total phosphate. Inositol pentakisphosphate (inositol‐ P 5 ), the major phosphorylated compound in the erythrocytes of most mature species of birds, is also present but in amounts approximately half that of inositol‐ P 4 . The effects of adenosine triphosphate, 2,3‐bisphosphoglyceric acid ( P 2 ‐glycerate), inositol‐ P 4 , inositol P 5 , and inositol hexakisphosphate (inositol‐ P 6 ) on the oxygen affinity of whole ‘stripped’ hemoglobin, hemoglobin A (major component), and hemoglobin D (minor component) isolated from erythrocytes of the mature ostrich have been determined. All five compounds cause a right shift in the oxygen dissociation curve of each hemoglobin and their relative effectiveness in decreasing the oxygen affinity is ATP < P 2 ‐glycerate < inositol‐ P 4 < inositol‐ P 5 < inositol‐ P 6 . No preferential interaction of inositol‐ P 4 or inositol‐ P 5 with either hemoglobin A or hemoglobin D was observed. The unique organic phosphate composition of the erythrocyte of the ostrich probably explains the relatively high whole blood oxygen affinity ( P 50 = 24.5 torr) of these birds.