Thermodynamical characteristics of the reaction of pyridoxal-5′-phosphate with L-amino acids in aqueous buffer solution

Autor: S. S. Guseinov, E. A. Venediktov, Valentin G. Badelin, V. P. Barannikov, I. N. Mezhevoi
Rok vydání: 2010
Předmět:
Zdroj: Russian Journal of Physical Chemistry A. 85:16-20
ISSN: 1531-863X
0036-0244
DOI: 10.1134/s003602441101002x
Popis: The reaction of pyridoxal-5′-phosphate with L-isomers of alanine, lysine, arginine, aspartic acid, glutamic acid, and glycine in phosphate buffer solution was studied by absorption spectroscopy and the calorimetry of dissolution at physiological acidity of the medium (pH 7.35). The formation constants of Schiff bases during reactions and changes in Gibbs energy, enthalpy, and entropy were determined. It was shown that the formation constant of the Schiff base and its spectral properties depend on the nature of the bound amino acid. The progress of the reaction with a majority of amino acids is governed by the entropy factor due to the predominant role of the dehydration effect of the reaction center of amino acids during chemical reactions. The intramolecular electrostatic interaction of an ionized phosphate group with the positively charged amino group on the end of the chain of amino acid residue stabilizes the Schiff bases formed by lysine and arginine. The extinction coefficient of the base, equilibrium constant, and the exothermic effect of the reaction then increase. The excess negative charge on the end of the chain of amino acid residues of aspartic and glutamic acids destabilizes the molecule of the Schiff base. In this case, the equilibrium constant decreases and the endothermic effect of the reaction increases.
Databáze: OpenAIRE
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