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

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).