Hemoglobins of reptiles. The primary structure of the major and minor hemoglobin component of adult Western Painted Turtle (Chrysemys picta bellii)

Abstract

Red blood cells of adult Western Painted Turtles (Chrysemys picta bellii) contain two hemoglobin components: HbA (alpha A2 beta 2) and HbD (alpha D2 beta 2). We present the complete amino-acid sequences of the alpha A-chains from the major component and of the beta-chains common to both components. Structural features are discussed with respect to the animals extreme tolerance of severe hypoxic conditions during hibernation which is accompanied by a high oxygen affinity of the hemoglobin. The strong ATP dependence of Western Painted Turtle hemoglobin oxygen affinity is contrasted by the loss of one ATP-binding site, beta 143(H21)-Arg----Leu. The primary structure of the beta-chains excludes an allosteric control mechanism by hydrogencarbonate as it was found in crocodiles. Except in turtles a hemoglobin pattern with HbA and HbD sharing the same beta-subunits has been found only in birds. In comparison to other vertebrate hemoglobins there is a surprising similarity of the sequences to those of bird hemoglobins. alpha A- as well as alpha D-chains show larger homologies to chains of the same type in different species than alpha A- and alpha D-chains to each other in the same species. This indicates a duplication of the alpha-gene preceding the divergence of turtles and birds.