Oxygen affinity and 2,3-diphosphoglycerate in blood of Australian marsupials of differing body size

Oxygen carriage and 2,3-diphosphoglycerate (2,3-DPG) levels have been measured in the blood of seven species of Australian marsupials ranging in size from 35 to 0.03 kg. They were Red and Grey Kangaroos, Wallaroo, Tammar Wallaby, Brush-tailed possum, Potoroo, and Brown Marsupial Mouse. Oxygen affinity decreased with decrease in adult body size, standard P50 (at 36 C) varying from 24.6 torr in the largest (Red Kangaroo) to 41.9 torr in the smallest (Brown Marsupial Mouse). The relationship between P50 and body size is similar to the relationship which has been described previously for eutherian mammals. The Bohr factor (--deltalog P50/deltapH) and value for Hill n were generally in the range found for other land-dwelling mammals. All species had 2,3-DPG in their erythrocytes acting as a regulator of oxygen affinity. The polymorphism at position beta 2 in hemoglobin of the Grey Kangaroo was shown to affect the respiratory properties of the molecule. When beta 2 = histidine, which has a positively charged side chain, erythrocyte 2,3-DPG was higher, and P50 was higher, than when beta 2 = glutamine which has a neutral side chain.