Structure-ionization relationship of tyrosine-containing peptides

The arid-base chemistry of tyrosine-containing peptides such as enkephalin, tyrosylglycylglycine, tyrosylglycine and analogous peptides is described. For each peptide and tyrosine derivative, microscopic and macroscopic acid dissociation constants and the thermodynamic parameters for proton dissociations were determined from pH-titrations and ultraviolet absorption spectra. The relative concentrations of various ionic forms for the peptides were calculated from the microscopic constants. The concentration ratio, represented by the tautomeric equilibrium constant (K(t)), showed a definite relationship to structure.