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 (DP G) concentration. The fetal bovine erythrocyte has six times the conce ntration of the allosteric modulator DPG compared with the adult cell, and yet the oxygen affinity of the fetal hemoglobin still exceeds tha t of the adult molecule at the respective physiological concentration of DPG and at physiological temperature. We find that the allosteric m odulator strongly affects the enthalpy of oxygen for the fetal hemoglo bin but not for the adult protein. We propose that this may be an impo rtant mechanism for the exchange of heat from mother to fetus. In part icular, under stripped conditions the oxygen affinity of fetal bovine Hb is considerably higher than that of the adult hemoglobin. Due to th e higher DPG concentration that characterizes fetal bovine erythrocyte s this difference is almost abolished in the presence of the respectiv e physiological concentration of DPG and at 20 degrees C. However, on going from 20 degrees C to 37 degrees C, the difference in O-2 affinit y 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 t he presence of DPG at physiological concentration. This behavior is re miniscent of that of human fetal Hb and outlines the role of temperatu re and of its interplay with heterotropic ligands in the modulation of hemoglobin function to fully meet the physiological needs of the orga nism. (C) 1996 Academic Press Limited