The amino acid sequences of the alpha and beta chains of hemoglobin from the snake, Liophis miliaris

The hemoglobin of Liophis miliaris has unusual properties. The hemoglobin is dimeric in the oxy form, and the cooperativity of O2 binding is very low, but both the Bohr effect and cooperativity are greatly enhanced in the presence of ATP (Matsuura, M. S. A., Ogo, S. H., and Focesi, A., Jr. (1987) Comp. Biochem. Physiol. 86A, 683-687). Four unique chains (2 alpha, 2 beta) can be isolated from the hemolysate. The amino acid sequences of one alpha and one beta chain have been determined in an effort to understand the functional properties. Comparison of the sequences with those of the alpha and beta chains of human Hb shows the following. (i) All 7 of the residues in the beta chain normally conserved in globins are identical to those of the human chain: Gly(B6), Phe(CD1), His(E7), Leu(F4), His(F8), Lys(H10), and Tyr(HC2), except that the distal His(E7) has been replaced by Gln in the alpha chain. (ii) All heme contact residues in the beta chain are identical with those in the human chain, but two differences are present in the alpha chain: the distal His(E7) is replaced by Gln and Met(B13) by Leu. (iii) All residues that form the binding site for organic phosphates are identical to those in human Hb. (iv) The major residues that contribute to the normal Bohr effect in human Hb, Asp-beta 94, His-beta 146, and Val-alpha 1 are conserved. (v) All beta chain residues at the alpha 1 beta 2 interface are identical with those in the human chain except two: Glu(G3)----Val and Glu(CD2)----Thr; these differences in charged residues may explain the dissociation to dimers. (vi) The 23 residues of the alpha chain in the alpha 1 beta 2 contact region are identical with those of the human chain except three: Phe(B14)----Leu, Thr(C3)----Gln and Pro(CD2)----Ser. (vii) A total of 17 differences occur at the alpha 1 beta 1 interface, 11 in the alpha chain and 6 in the beta chain.