Equilibrium Constants of Interaction between Pyridoxal-5'-Phosphate Coenzyme and Glycine and Its Oligopeptides in Aqueous Buffered Saline

Electronic absorption spectroscopy is used to study the patterns of bonding of oligopeptides of glycyl-glycine and glycyl-glycyl-glycine using the coenzyme pyridoxal-5'-phosphate at 293 K in a phosphate buffer solution at pH 7.35. The results are compared to the similar process for monomeric glycine. The interaction constants and the spectral parameters of the reaction products are determined. The observed increase in the peptide–coenzyme bonding equilibrium constants in the Gly–(Gly–Gly)–(Gly–Gly–Gly) series is due to a drop in the basicity of the reaction’s amino group and an increase in the proportion of peptides with non-ionized amino groups in the solution. An increase in the chain length of the peptide is accompanied by a reduction in the coefficient of extinction of the resulting Schiff base.