THERMODYNAMICS OF OXYGEN BINDING TO ARCTIC HEMOGLOBINS - THE CASE OF REINDEER

The most surprising characteristic of reindeer hemoglobin (Hb) concerns its response to changes in temperature. Thus, the shape of the oxygen-binding curve is strongly temperature dependent due to the difference in the enthalpy of oxygenation between the T and R state of the molecule. In fact, Δ H of oxygen binding to the T state is strongly exothermic whereas that of the R state is very close to zero or possibly positive after correction for the heat of oxygen solubilization. Moreover, the allosteric transition To a- Ro has been found to display a negative Δ H and a contemporaneous decrease in entropy, a behavior which is precisely the opposite of what has been reported for other hemoglobins. As a whole, reindeer Hb represents a beautiful example of the significance that comparative studies may have in assessing the general validity of the main properties of the hemoglobin molecule. © 1990.