DETERMINATION OF THE RATES OF FORMATION AND HYDROLYSIS OF THE SCHIFF-BASES FORMED BY PYRIDOXAL 5'-PHOSPHATE AND COPOLYPEPTIDES CONTAINING L-LYSINE

Abstract

We determined the apparent rate constants of formation (k1) and hydrolysis (k2) of the Schiff bases formed between pyridoxal 5'-phosphate (PLP) and L-lysine and L-alanine copolymers of different compositions, as well as those formed between PLP and L-lysine and L-glutamic acid copolymers, at various pH values, a temperature of 25-degrees-C and an ionic strength of 0.1 M. The k1 values obtained in neutral and acidic media were independent of the copolymer composition. The efficiency of the intramolecular acid catalysis for the formation of the Schiff bases was found to be somewhat higher than that of PLP-primary amine systems (the slope of the Bronsted plot was alpha=0.77). The most stable of the Schiff bases studied was that with a protonated imine nitrogen and phosphate group and an unprotonated pyridine nitrogen.