OXYGEN BINDING PROPERTIES OF HEMOGLOBIN FROM THE WHITE RHINOCEROS (Ifl2"GLUI) AND THE TAPIR

The ,8-chain of rhinoceros hemoglobin contains glutamic acid at position ,82, an important site for the binding of organic phosphates. We have investigated the oxygen binding properties of this hemoglobin and its interaction with ATP, 2,3-diphosphoglycerate, CO 2 and chloride. The results show that the presence of GLU at position ,82 nearly abolishes the effect of organic phosphates and CO2, whereas the oxygen-linked binding of chloride is not affected. Thus rhinoceros hemoglobin has only protons and chloride anions as major allosteric effectors for the control of its oxygen affinity. From the results obtained with hemoglobin solutions it can be calculated that the blood oxygen affinity of the rhinoceros must be rather high with a Ps0 of about 20 tort at pH 7.4 and 37 °C, which conforms with observations obtained for other large mammals. Allosteric factors Organic phosphates Bohr effect Oxygen affinity Chloride At the present time, the small mammalian order Perissodactyla includes three families: the Equidae, which are the largest group, the Tapiridae and the Rhinocerotidae. Hemoglobin sequences and functional studies have only been obtained for hemoglobins of the Equidae group (cf. Mazur and Braunitzer, 1982; Matsuda et al., 1980). All species of this group have glutamine at position f12, one of the binding sites for 2,3-diphosphoglycerate (2,3-DPG), which in human hemoglobin is occupied by histidine (Arnone, 1972). However, experiments with horse hemoglobin have shown that the substitution is apparently of little consequence for the effect of organic phosphates (Bunn and Kitchen, 1973; Braunitzer et al., 1978). In contrast to the above results, the recently published primary structure of the hemoglobin from the white rhinoceros (Cerathother ium sinum) shows a glutamic acid residue at position f12 (Mazur et al., 1982). Glutamic acid at position f12 has not been demonstrated in any other mammalian hemoglobin, but is present in Accepted/or publication 13 January 1984 0034-5687/84/$03.00 © 1984 Elsevier Science Publishers B.V.