The haemocyanin of the tarantula Lasiodora erythrocythara—the influence of CO 2, organic cofactors and temperature on oxygen affinity

Abstract

1. 1. Whole blood oxygen equilibrium curves for the haemocyanin of the Honduran tarantula Lasiodora erythrocythara have for the first time been investigated in vitro. 2. 2. Oxygen affinity was pH dependent with a mean Bohr coefficient of −0.71 ± 0.06 between pH 7.3 and 8.1. At 25°C and pH 7.6 the P 50 value was 23 Torr. 3. 3. The fixed acid Bohr effect was not significantly different from the CO 2 Bohr effect indicating the lack of a specific effect of CO 2 on oxygen affinity. 4. 4. Dialysis had no measurable effect on haemocyanin oxygen affinity, indicating the absence of unidentified dialysable factors. The haemocyanin was also insensitive to changes in the concentration of d and l lactate, succinate, guanosine and urate. 5. 5. Temperature was found to have little influence on oxygen affinity between 20 and 25°C illustrated by the low Δ H value of −5.6 kJ mol −1. At the temperature extremes of 15 and 30°C Δ H values increased to −29kJmol −1. 6. 6. Cooperativity, expressed as n 50, was both temperature and pH dependent.