An Investigation of Haemocyanin Oxygen Affinity in the Semi-Terrestrial Crab Ocypode Saratan Forsk

The oxygen affinity of the haemocyanin in the supralittoral crab Ocypode saratan was investigated at temperatures between 20 and 35 °C. The effect of L-lactate on dialysed and undialysed haemolymph oxygen affinity was also examined. In general, the temperature sensitivity of the haemocyanin was low: δH was −3.1kJ mol−1, between 25 and 30°C. Temperature sensitivity was temperature-dependent, being larger at the extreme temperatures (ΔH = −26kJ mol−1). The Bohr effect (ΔlogP50/ΔpH) was temperature-independent and averaged - 0.67. No specific effect of CO2 on oxygen affinity was observed but L-lactate increased oxygen affinity in both dialysed and undialysed haemolymph. The maximal effect of lactate on oxygen affinity was similar in dialysed and undialysed haemolymph, but was evident at a lower lactate concentration (4mmol1−1) in dialysed, compared with undialysed, haemolymph (7mmoll−1). Dialysed haemolymph showed a higher oxygen affinity than undialysed haemolymph at low lactate concentration (<4mmoll−1). The Bohr effect and buffer value both decreased with increasing lactate concentration in both dialysed and undialysed haemolymph. The physiological implications of these findings are discussed.