Enzymes as synthetic catalysts: mechanistic and active-site considerations of natural and modified chymotrypsin

This paper describes the mechanistic investigation of {alpha}-chymotrypsin and (Met{sub 192}-sulfoxide)-{alpha}-chymotrypsin-catalyzed peptide synthesis in a kinetically controlled process (i.e., aminolysis) and the relative stabilities of both enzymes in different conditions. Partitioning parameters for various nucleophiles (including D- and L-amino acids) competing with water for the acyl enzyme intermediate were determined. these parameters provide insights into the active-site geometries of both the native and the oxidized enzymes. {alpha}-Chymotrypsin with D-isomer selectivity in the hydrolysis of {alpha}-methyl-{alpha}-nitro esters was used for the synthesis of a D-L pseudopeptide. Molecular modeling together with kinetic results was used to explain the unusual phenomena in hydrolysis and synthesis catalyzed by the native and modified enzymes. {alpha}-Chymotrypsin methylated at the {epsilon}{sub 2}-N of the active-site histidine was shown to be an effective catalyst for peptide synthesis in the kinetically controlled process. No peptide bond hydrolysis was observed.