ABSTRACT
The implication, from the point of view of peptide bond formation at physiological pH values, is that significant thermodynamic work is required for the transfer of a proton from the protonated a-amino group of one reactant to the deprotonated a-carboxyl group of the other reactant. In practice, due to their amphoteric nature, amino acids and peptides are ionized over the entire pH range. Furthermore, at pH values between about 3 and 9, they exist in a dipolar, or zwitterionic form, and in the physiological pH region they are almost completely ionized. Under these circumstances, proteolysis will be largely favored over proteosynthesis. In a purely formal sense, one might interpret the endergonic process of peptide bond formation from ionized amino acid residues as the sum of the energy-releasing step of peptide bond synthesis from nonionized amino acids and the energy-consuming step of the proton transfer.
