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 ≅ 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 ≅ 10 2 M −1. The deoxyhemoglobin constant values markedly decrease as a function of pH, becoming, at pH 8.5, about K D ≅ 10 3 M −1 whereas for the oxyhemoglobin the constants remain of about the same, K O ≅ 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 amino acid residue differences were found in the β-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 β (G3) instead of Glu 101 β (G3). The substitutions could provide an un-neutralized, positively charged, residue Lys-104β 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.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
More From: Comparative Biochemistry and Physiology -- Part B: Biochemistry and Molecular Biology
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.