Oxygen Binding of Monotreme Haemoglobins I. Oxygen Binding Parameters of the Haemoglobins of Platypus, Ornithorhynchus anatinus, and Echidna, Tachyglossus aculeatus

Abstract

Oxygen binding parameters have been determined for echidna and platypus haemolysates. At pH 7· 1 and 25°C platypus haemoglobin with an oxygen half-saturation pressure (Pso) of 2·4 kPa has a lower oxygen affinity than echidna haemoglobin with a Pso of 1·6 kPa. The AHo of oxygenation of platypus haemoglobin is -38·9kJ/mol which is more exothermic than the -29·7kJ/mol of echidna haemoglobin. Platypus haemoglobin has a steeper alkaline Bohr curve than echidna haemoglobin, while both haemoglobins show high levels of cooperativity at various temperatures and pH values. It appears that diphosphoglyceric acid modulates the affinity of echidna and platypus haemoglobins to different extents. This information is interpreted in terms of the steric effects of ligand binding originating in the amino acid sequence differences of these two species.