Temperature sensitivity of the oxygenation reaction of stripped haemolysates from the freshwater fishes Labeo capensis and Ciarias gariepinus

Abstract

The oxygen binding properties of haemoglobin solutions of the mudfish Labeo capensis and the catfish Clarias gariepinus, stripped by gel filtration chromatography and buffered at 23°C in 0,05 M Hepes (pH 7,48), were determined at 8°C, 15°C and 23°C. The P₅₀ values obtained for L. capensis at these respective temperatures were 0,89 (pH 7,63); 1,29 (pH 7,52) and 3,02 (pH 7,49) and those for C. gariepinus haemoglobin were 2,47 (pH 7,61 ); 3,34 (pH 7,53) and 6,30 (pH 7,49). The lower oxygen affinity of C. gariepinus haemoglobin may be related to the obligatory air breathing of C. gariepinus by means of a branchial organ which is absent in the mudfish. The purified hemolysate from C. gariepinus also displayed higher haem-haem co-operativity (n) at all three experimental temperatures compared to L. capensis. The heat of oxygenation (ΔH) between 8°C (pH 7,63) and 23°C (pH 7,49) calculated for L. capensis haemoglobin (−56,3 kJ.mol¹) exceeded that of C. gariepinus (−43,1 kJ.mol¹).