Peptide equilibrium controlled enzymatic

When one is using proteases in a direct reversal of their normal hydrolytic function, the equilibrium position is very important in limiting the attainable yield in equilibrium-controlled enzymatic peptide synthesis. If both reactants and products are largely undissolved in the reaction medium as suspended solids, thermodynamic analysis of such a system shows the reaction will proceed until at least one reactant has dissolved completely, towards either products or reactants ( switchlike behavior). In case of a favorable equilibrium for synthesis, the yield is maximized in the solvent of least solubility for the starting materials (Hailing, 1995). Thermolysin-catalyzed reactions ofX-Phe-OH (X = formyl, Ac, Z) with Leu-NH2 yielded X-Phe-Leu-NH2 with equilibrium yields > 90% over a range of solvents. Some predictions, such as a linear decrease in yield with the reciprocal of the initial reactant concentrations, could be verified (Hailing, 1995). 

Principle of enzymatic peptide synthesis, (a) Synthesis under thermodynamic control is based on microscopic reversibility. The overall equilibrium constant will be strongly dependent on ionization constants of the different species and the reaction pH. 

---