THE HEMOGLOBINS OF THE BULLFROG, RANA-CATESBEIANA - THE CDNA-DERIVED AMINO-ACID-SEQUENCES OF THE ALPHA-CHAINS OF ADULT HEMOGLOBIN-B AND HEMOGLOBIN-C - THEIR ROLES IN DEOXYGENATION-INDUCED AGGREGATION

The adult bullfrog (Rana catesbeiana) has two major tetrameric hemoglo bins, B and C, which share a common beta chain but have different alph a chains. Components B and C associate upon deoxygenation to form a co mplex of the form BC2, a trimer of tetramers that depends on contacts between the alpha(B) and alpha(C) chains. Nucleotide sequences of cDNA transcripts for these chains have been determined. Transcripts were i dentified by analysis of the amino acid compositions of the tryptic pe ptides of the components and by partial amino acid sequencing. These r esults, together with the amino acid sequence of the beta chain (Tam, L.-T., Gray, G. P., and Riggs, A. F. (1986) J. Biol. Chem. 261, 8290-8 294), permit an analysis of the structures of the alpha2beta2 tetramer s of hemoglobins B and C. Molecular modeling suggests possible residue s at the alpha(B)-alpha(C) interfaces in the BC2 trimer and additional alpha(C)-alpha(C) contacts that would form a closed ring of six alpha chain subunits that would further stabilize the BC2 trimer. Phylogene tic analysis of the alpha(B) sequence suggests that it may be a ''tadp ole'' chain, the temporal expression of which has shifted from larva t o adult.