Hemoglobins of the tadpole of the bullfrog, Rana catesbeiana. Amino acid sequence of the beta chain of a major component.

The amino acid sequence of the /3 chain of component HI of the hemoglobin of the tadpole of the bullfrog, Rana catesbeiana, has been determined.Comparison of this sequence with the 117 identified residues of the / 3 chain in the adult bullfrog shows that 50% (59 of 117) of the residues are identical; 55% (81 of 146) are identical in the comparison with the human /3 chain.Tadpole hemoglobin lacks most of the residues believed responsible for the alkaline Bohr effect in human hemoglobin: the NH2 terminus is acetylated and histidine H5 ((~122) in the human a chain is replaced by glutamine in the tadpole.Although the tadpole fl chain has a COOHterminal histidine, the hydrogen bond responsible in human hemoglobin for about one-half the normal alkaline Bohr effect cannot form, because asparagine rather than aspartate is present at position 94.How- ever, histidyl residue HZ1 @143), invoked to explain the reversed "acid" Bohr effect in human hemoglobin, is present in the tadpole chain and is adjacent to a seryl residue @144) rather than a lysyl residue, so that the pK of the /3143 histidine should be higher than in human hemoglobin.This could explain the substantial acid Bohr effect in tadpole hemoglobin.