Specific effects of thiosulphate and L-lactate on hemocyanin-O2 affinity in a brachyuran hydrothermal vent crab

Abstract

The hydrothermal vent crab Bythograea thermydron Williams (Brachyura: Bythograeidae) is exposed to high environmental concentrations of hydrogen sulphide. Hydrogen sulphide has previously been shown to be oxidized to a non-toxic form, thiosulphate (S2O3 2-), that accumulates in the hemolymph (to concentrations>1 mmoll-1). Hemocyanin-oxygen (Hc-O2) affinity was determined in dialysed, fresh or frozen hemolymph samples from B. thermydron. Although freezing is known to alter the affinity or cooperativity of some decapod crustacean hemocyanins, neither Hc-O2 affinity nor cooperativity was significantly altered in B. thermydron hemolymph samples that had been frozen, consistent with previous findings. Oxygen affinity of B. thermydron hemocyanin was significantly increased by the presence of L-lactate. Likewise, Hc-O2 affinity was significantly increased by the presence of 1.5 mmol S2O3 2- I-1. The magnitude of this effect was the same as for similar concentrations of L-lactate. This specific effect of S2O3 2- does not appear to be a general property of crustacean hemocyanins, as there was no significant effect of S2O3 2- on Hc-O2 affinity or cooperativity in dialysed hemolymph samples from the brachyuran crabs Cancer anthonyi Rathbun and C. antennarius Stimpson, or the thalassinid ghost shrimp Callianassa californiensis Dana. In the context of high environmental sulphide concentrations coupled with low PO 2, and the subsequent accumulation of S2O3 2- in crab hemolymph, the increase in Hc-O2 affinity due to thiosulphate appears to be an adaptive response in B. thermydron.