ON THE STABILITY OF THE SCHIFF-BASES OF PYRIDOXAL 5'-PHOSPHATE WITH POLYPEPTIDES CONTAINING L-LYSINE

We determined the apparent equilibrium constant of formation, K(pH), of the Schiff bases of pyridoxal 5'-phosphate (PLP) and poly- and copolymers containing L-lysine, as a function of pH at 25-degrees and a constant ionic strength of 0.1M. The k(pH) values obtained at acidic and neutral pH were larger that those reported for Schiff bases of PLP and hexylamine. We determined calorimetrically DELTA-H of formation of Schiff bases of PLP and poly(L-lysine) (-4.5 kcal/mol), and PLP and hexylamine (-3.4 kcal/mol) at pH 7.00. Semi-empirical theoretical calculations (INDO and AM1 methods) of a model compound of Schiff base of PLP and polypeptide containing L-lysine show the capability of specific interactions between groups of PLP and the peptide skeleton.