Effects of carbon dioxide and organic phosphates on the O 2 binding properties of purified turtle hemoglobin at 3° and 20°C

Potential contributions of multiple hemoglobins for enhanced blood O 2 transport during winter submergence and summer activity were evaluated for the common map turtle ( Graptemys geographica ). Hb’s 1 and 2 were separated, purified and prepared in physiological media ([Hb 4 ] = 1 mM); O 2 equilibrium curves were generated by thin‐film techniques. At 3°C and pH 7.6, the half‐saturation PO 2 (P 50 ) for Hb’s 1 and 2 were 3.4 ± 0.3 and 6.5 ± 0.3 Torr, respectively. The corresponding CO 2 ‐Bohr slopes (Δlog P 50 /ΔpH) were −.06 ± .04 and −.31 ± .02, respectively. Additions of ATP and DPG had no effect on the O 2 binding properties of Hb 1, and only minor effects on Hb 2. At 20°C and pH 7.1, P 50 for Hb’s 1 and 2 were 4.8 ± 0.4 and 12.5 ± 0.4 Torr, respectively. Temperature coefficients (Δlog P 50 /ΔT°C) for the two Hbs were 0.01 and 0.02, respectively. CO 2 ‐Bohr slopes for Hb’s 1 and 2 were −.09 ± .01 and −.45 ± .05, respectively. ATP and DPG significantly increased P 50 and Δlog P 50 /ΔpH for both Hbs at 20°C. O 2 binding properties for the turtle Hb mixture (60% Hb 1 + 40% Hb 2) at 3°C most closely resembled those of Hb 1. At 20°C, O 2 transport characteristics for the Hb mixture revealed a more substantial contribution of Hb 2. These findings suggest that the elevated Hb‐O 2 affinity and reduced CO 2 ‐Bohr effect of Hb 1 promotes extrapulmonary O 2 loading during prolonged winter submergence. For the summer‐active animal, the increased P 50 and Δlog P O2 /ΔpH of Hb 2 enhances the off‐loading of oxygen. (Supported by DePaul Univ. LA&S and URC grants)