Determination of the rates of formation and hydrolysis of the Schiff basesformed by pyridoxal 5 '-phosphate with copolypeptides containing L-lysine and aromatic L-amino acids

The apparent rate constants of formation (k(1)) and hydrolysis (k(2)) of th e Schiff bases formed between pyridoxal 5'-phosphate and the poly(L-Lys, L- Trp)4:1 copolymer at different pH values, a temperature of 25 degrees C and an ionic strength of 0.1 M were determined. The individual rate constants of formation and hydrolysis of the Schiff bases of pyridoxal 5'-phosphate w ith poly(L-Lys,L-Trp)4: 1, poly(L-lys, L-Tyr)4 :1, and poly(L-Lys, L-Phr)1: 1 corresponding to the different chemical species present in the medium as a function of its acidity were also determined, as we:re the pK values for the Schiff bases. The significance of the interactions between the pyridine ring in pyridoxal 5'-phosphate and the aromatic ring in the L-phenylalanin e, L-tyrosine, and L-tryptophan side chains is demonstrated.