Oxygen transport by fetal bovine hemoglobin.

The functional properties of fetal bovine hemoglobin have been studied as a function of temperature, chloride and 2,3-diphosphoglycerate (DPG) concentration. The fetal bovine erythrocyte has six times the concentration of the allosteric modulator DPG compared with the adult cell, and yet the oxygen affinity of the fetal hemoglobin still exceeds that of the adult molecule at the respective physiological concentration of DPG and at physiological temperature. We find that the allosteric modulator strongly affects the enthalpy of oxygen for the fetal hemoglobin but not for the adult protein. We propose that this may be an important mechanism for the exchange of heat from mother to fetus. In particular, under stripped conditions the oxygen affinity of fetal bovine Hb is considerably higher than that of the adult hemoglobin. Due to the higher DPG concentration that characterizes fetal bovine erythrocytes this difference is almost abolished in the presence of the respective physiological concentration of DPG and at 20 degrees C. However, on going from 20 degrees C to 37 degrees C, the difference in O2 affinity between the two hemoglobins is restored, as it should if oxygen has to be transferred from maternal to fetal blood, by virtue of the lower overall heat of oxygenation (delta H) displayed by fetal Hb when in the presence of DPG at physiological concentration. This behavior is reminiscent of that of human fetal Hb and outlines the role of temperature and of its interplay with heterotropic ligands in the modulation of hemoglobin function to fully meet the physiological needs of the organism.