The Hemoglobins of the Bullfrog, Rana catesbeiana

At least two electrophoretically distinct components of hemoglobin, B and C, occur in hemolysates of the bullfrog, Rana catesbeiana (Aggarwal, S.J., and Riggs, A. (1969) J. Biol. Chem. 244, 2372–2383). Component C polymerizes by disulfide bond formation between tetramers, but component B does not. Component C also has a higher oxygen affinity and a smaller Bohr effect than does component B. The amino acid sequence of the first 105 of 141 residues has been determined for the β chain of component C. The sequences of segments of the remaining 35 residues have also been determined. The first 105 residues together with these segments differ in 29 of the 125 identified positions (excluding one deletion and one insertion) from the corresponding segment of the β chain of the European frog, Rana esculenta (CHAUVET, J.-P., AND ACHER, R. (1972) Biochemistry 11, 916–927). This large difference suggests that these frogs, although in the same genus, may have been separated from one another for as long as 150 to 250 x 106 years if the procedure of Dickerson ((1971) J. Mol. Evol. 1, 26–45) is assumed. Alignment of the sequence with that of the human β chain shows that the first 6 residues of the NH2-terminal segment of the human chain are absent in the bullfrog β chain. Among the remainder (125 residues in the bullfrog), 67 of 125 (54%) are identical. In mammalian hemoglobins a hydrogen bond between the imidazole group of the histidyl residue at β146 and the aspartyl residue at β94 appears responsible for about half the Bohr effect. The position corresponding to this aspartyl residue is a glycyl residue at β88 in the bullfrog. Therefore, if the COOH-terminal histidine of the β chain is involved in the Bohr effect it must be hydrogen-bonded to a different residue in unliganded bullfrog hemoglobin.