Temperature effects on protease catalyzed acyl transfer reactions in organic media

The influence of reaction temperature on synthesis activity, product yield and nucleophile specificity for alpha-chymotrypsin and subtilisin Carlsberg were studied. The enzymes were immobilized on Celite and used in acetonitrile with a water content of 10%. Acyl-transfer reactions with Ac-PheOEt as acyl donor and 11 different amino acid amides and 3 dipeptides as nucleophiles were studied. The decrease in temperature from 25 to -1 degrees C had a positive effect on the peptide yield in all reactions studied. The most efficient nucleophiles for the two enzymes alpha-chymotrypsin and subtilisin Carlsberg is arginine amide and glycine amide, respectively. When decreasing the reaction temperature the yield for alpha-chymotrypsin increased from 86 to 94% with arginine amide as nucleophile and for subtilisin the yield increased from 75 to 84% for glycine amide. The nucleophile specificity was determined as the p value, which describes the competition between nucleophile and water for the acyl enzyme. alpha-Chymotrypsin showed preference for both small and positively charged amino acid residues and subtilisin preferred small uncharged nucleophiles. The temperature did not affect the specificity order but all nucleophiles became more effective in the competition with water at low temperature. In addition, the results indicate that the temperature effect is more pronounced for the smaller nucleophiles.