Haemoglobin O2 binding in newborn and adult rabbits

The relationship between haemoglobin O2 saturation and 2,3-diphosphoglycerate concentration (2,3-DPG) in haemoglobin solutions equilibrated with 3.7% O2-5.7% CO2 were identical in newborn and adult rabbits over a wide range of 2,3-DPG (0.5-40.0 mumol g-1 Hb), and independent of the haemoglobin concentration (1-10 g dl-1). Also, the resistance of the haemoglobin to alkali denaturation and the spectrophotometric absorption spectra of carboxy and oxyhaemoglobin between 500 nm and 650 nm, as well as the isoelectric focusing pattern of the haemoglobin after early and late stabilization with CO, were the same in newborn and adult animals. Both demonstrated one dominant band, focusing at pH 7.17, and one less conspicuous at pH 7.40. The erythrocyte pH was higher in the newborn than in the adult animals. Isoelectric focusing of erythrocyte pyruvate kinase demonstrated two isoenzyme bands in the newborn animals, one dominant fraction at pH 5.85 and one minor fraction at pH 7.97, whereas only the pH 7.97 band was observed in the adult. It is concluded that the physical properties of the haemoglobin molecule itself are the same in newborn and adult rabbits, and that the postnatal decrease in haemoglobin O2 affinity is solely due to changes in the erythrocyte metabolism, leading to a marked rise in 2,3-DPG and a minor decline in erythrocyte pH. The rise in 2,3-DPG is caused by decrease of pyruvate kinase, probably due to proteolytic inactivation of the enzyme.