Organic phosphate-hemoglobin interactions appear non-adaptive in the hypoxic toad, Bufo marinus

Abstract

1. 1. The hemoglobin oxygen affinity of “stripped” hemolysate from Bufo marinus was sensitive to the allosteric cofactors ATP and 2,3-diphosphoglycerate which occur in toad erythrocytes. 2. 2. The affinity constants were not appreciably affected by changes in inorganic ions in the concentration range likely to be of physiological significance. 3. 3. The P 50 of toad blood of pH 7.9 and pCO 2 = 7.2 mmHg was 56.7 ± 3.1 mmHg at 30°C, with Hill's coefficient, n = 2.8. 4. 4. The P 50 was not significantly changed following 11–14 days hypoxic acclimation of the toads at pO 2 = 31 mmHg, 28°C, despite a significant rise in 2,3-DPG from 28.3 ± 3.2 to 35.1 ± 2.5 μmol/gHb. 5. 5. These data suggest that phosphate-hemoglobin interactions are not adaptive in the sense of having been scrutinised by natural selection, but are part of a package of regulatory mechanisms reflecting phenotypic plasticity. The inherent dangers of extrapolation from molecular to physiological studies are emphasised.