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|Type:||Artigo de periódico|
|Title:||INTERACTIONS OF ADENOSINE-TRIPHOSPHATE WITH SNAKE HEMOGLOBINS - STUDIES IN LIOPHIS-MILIARIS, BOA-CONSTRICTOR AND BOTHROPS-ALTERNATUS|
|Abstract:||The hemoglobins of three snake species: Liophis miliaris, Bothrops alternatus and Boa constrictor present a single ATP binding site per tetramer. The ATP association constant values for the deoxyhemoglobins at pH 7.5 were about K-D congruent to 10(6) M(-1) (10(7) M(-1) for B. contrictor), three to four orders of magnitude higher than the respective values for oxyhemoglobin of about K-O congruent to 10(2) M(-1). The deoxyhemoglobin constant values markedly decrease as a function of pH, becoming, at pH 8.5, about K-D congruent to 10(3) M(-1) whereas for the oxyhemoglobin the constants remain of about the same, K-O congruent to 10(2) M(-1), at the pH range studied. The high ATP binding affinity constants, compared to those of human hemoglobin A, were explained from a molecular structural standpoint, considering L. miliaris hemoglobin, whose complete primary sequence is known. Two distinct aminoacid residue differences were found in the beta-chain, one being Trp (NA3) (more hydrophobic) in the snake hemoglobin which substitutes the Leu (NA3) in human hemoglobin, and the second being Val 101 beta (G3) instead of Glu 101 beta (G3). The substitutions could provide an un-neutralized, positively charged, residue Lys-104 beta and, taking into account its high pK value, the pH dependence of ATP binding affinity for the snake hemoglobin would originate from pH-dependent ionization of phosphate groups of the allosteric effector. The physiological implications of the high ATP binding constant, as well as the possible protective role of the nucleotide binding against the effect of high environmental temperatures on the oxygen dissociation curves, are discussed.|
|Editor:||Pergamon-elsevier Science Ltd|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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