Oxygenation properties of hemoglobin from the turtle Geochelone carbonaria

ABSTRACT

The oxygen-binding properties of hemoglobin (Hb) from the adult terrestrial turtle Geochelone carbonaria are described. Turtle hemoglobins have a low intrinsic oxygen affinity and a low sensitivity to an endogenous cofactor (ATP) usually present at high concentrations in the reptile erythrocytes. The amplitude of the Bohr effect for O2 binding was virtually the same in the absence and presence of saturating ATP concentrations (deltalogP50/deltapH, about -0.60) and increased in the total hemolysate (-0.83). The large Bohr effect found in G. carbonaria Hb may be important for 02 delivery to the tissue. The degree of cooperativity displayed by Hb for 02 binding ranged between 1.5 and 2.0 in stripped solution and total hemolysate. These observations suggest the stability of the low affinity conformation, which needs to be confirmed by additional experiments.