Structural and functional characterization of hemocyanin from the anemone hermit crab Dardanus calidus.

Oxygen-binding to haemocyanin (He) is generally an exothermic process, with overall enthalphy of oxygenation varying from species to species. A number of crustacean Hcs showed a null or reduced enthalphy of oxygenation, among others, the anomuran Pagurus bernhardus and Paralithodes camtscaticae possess a completely temperature-independent oxygen-binding in a wide range of temperature and pH. Functional analysis performed on purified native, hexameric and dodecameric He forms of the anemone hermit crab Dardanus calidus allowed to calculate the enthalphy of oxygenation values that resulted equal to - 36.2, - 33.8 and - 26.8 kJ/ mol, respectively. Thus, the temperature sensitivity of oxygen binding of D. calidus He is in contrast with the temperature independence reported for P. bernhardus and P. camtscaticae, suggesting a high He functional heterogeneity within Anomura. Functional characterization also evidenced a strong oxygen affinity modulation by protons (Delta logP(50)/Delta pH=-0.97) and lactate [Delta logP(50)/Delta log(lactate)=-0.38], and a significant decrease in cooperativity by physiological concentration of lactate (n(50) from 2.8 to 1.7 at pH 7.5).