Reduced sensitivity of O2 transport to allosteric effectors and temperature in loggerhead sea turtle hemoglobin: functional and spectroscopic study

The functional and spectroscopic (EPR and absorbance) properties of the adult loggerhead sea turtle (Caretta caretta) hemoglobin have been studied with special reference to the action of allosteric effectors and temperature. Present results indicate that turtle Hb displays a very low O₂ affinity and a very small sensitivity to allosteric effectors and temperature. Furthermore, the amplitude of the Bohr effect for O₂ binding is strongly reduced. In parallel, EPR and absorbance spectroscopic properties of the nitrosylated derivative of turtle Hb suggest that the hemoprotein is in low-affinity conformation, even in the absence of allosteric effectors. These findings suggest the existence of unusual molecular mechanisms modulating the basic reaction of Hb with O₂, which may be linked to specific physiological needs related to the diving behavior of the turtle.