The CO2-specific sensitivity of hemocyanin oxygen affinity in the decapod crustaceans

The CO2-specific sensitivity of hemocyanin oxygen affinity and oxygen binding site cooperativity were investigated in five species of crabs. The hypothesis that CO2-specific effects on hemocyanin are related to the molecular CO2 concentrations that occur naturally in crab hemolymph was tested in crabs that experience a variety of hemolymph CO2 pressures. Crab species were chosen from subtidal, intertidal, and semiterrestrial habitats. Hemolymph samples from each species were added to physiological salines buffered with 50 mM HEPES. O2 equilibrium curves were determined spectrophotometrically by gassing the hemolymph-saline mixtures with different P at constant P and temperature. We found no CO2-specific effects on oxygen equilibrium properties of hemocyanin in any species under the conditions investigated. It is concluded that molecular CO2 and bicarbonate ions are not important in directly modulating the oxygen equilibrium properties of crustacean hemocyanins.