OXYGEN-HEMOCYANIN RELATIONSHIPS IN THE LAND CRAB, CARDISOMA GUANHUMI

Abstract

The hemocyanin of Cardisoma has a high O2 affinity, the pressure of half-saturation at 25[degree]C and pH 7.5 being about 4 mm O2. The O2 equilibrium curve is sigmoid, with a moderately high degree of interaction occurring among the O2 combining sites of the molecule ("n" averages 2.6). A normal Bohr effect, with a Phi value of -0.75 for the pH interval 7.3-7.8, is present. The Co capacity of the blood averaged 2.8 volumes percent O2. O2 analyses of pre-branchial and post-branchial blood samples indicated that the hemocyanin did not become saturated with O2 as it passed through the gills, that nearly all the O2 present was in combination with the hemocyanin, and that the O2 partial pressures in the blood were very low. Unusually high concentrations of CO2 were found in the blood. The high O2 affinity of this hemocyanin is altered only very slightly by environmental temperature changes. It is suggested that the high O2 affinity may be a secondary adaptation tending to counter the adverse effects of water conserving adaptations of the branchial chamber on the rate of O2 diffusion through the gills. It is tentatively concluded that, though the hemocyanin of de-capod crustaceans may serve several functions and may not always be essential for respiration, its primary function being that of a blood respiratory pigment.