Optimization of Protease-Catalyzed Acyl Transfer Reactions. Determination of the Partition Constant Characterizing Nucleophile Efficiency

The partitioning of the acyl-enzyme between aminolysis by an added nucleophile and hydrolysis plays a key-role in protease-catalyzed acyl transfer reactions. It can be characterized by the partition constant, which is equal to the nucleophile concentration for which aminolysis and hydrolysis proceed at the same velocity. We describe a method for calculation of the partition constant from the product ratio which is based on the integrated rate equation. Therefore, it can be applied to reactions performed under synthesis-like conditions, i.e. a high degree of nucleophile consumption during the reaction. In principle, the dependence of the partition constant on nucleophile concentration can be determined from a single reaction. V8-protease-catalyzed acyl transfer reactions using Z-Glu-OMe as acyl donor and amino acid amides as nucleophiles were investigated as an application of the method. The central role of the partition constant in optimization of preparative protease-catalyzed acyl transfer reactions is discussed.