Hemoglobins of reptiles. The primary structures of the alpha I- and beta I-chains of common iguana (Iguana iguana) hemoglobin

Abstract

The primary structures of alpha I- and beta I-chains from the hemoglobins of the Common Iguana (Iguana iguana) are presented. The globin chains were separated on CM-cellulose in 8 M urea buffer. The amino-acid sequences were established by automatic Edman degradation of the native chains, the tryptic peptides and a peptide obtained by cyanogen bromide cleavage. The sequences are compared with human hemoglobin. Amino-acid replacements at positions critical for structure and function of the hemoglobin are discussed. The requirements for binding of ATP and also of DPG as allosteric effectors at the beta-chains seem to be fulfilled. Comparison of the alpha-chains with those of the Viper (Vipera aspis) shows 66 amino-acid substitutions. This number is in the same order of magnitude as the ones found by comparison with alpha-chains of crocodiles and mammals as well as with alpha A-chains of a turtle and birds. This result points towards a period of independent evolution of the reptile lines leading to the Common Iguana on one hand and to the Viper on the other. This time span is comparable to the one separating mammals from reptiles.