ORGANIC-REACTIONS CATALYZED BY MODIFIED ENZYMES .1. ALTERATION OF THE SUBSTRATE-SPECIFICITY OF ALPHA-CHYMOTRYPSIN BY THE MODIFICATION PROCESS

The substrate specificity of some modified alpha-chymotrypsin derivatives in the synthesis of peptides, using natural and synthetic acyl donors and several nucleophiles, is studied. A systematic study of the alteration of active sites by the modification method is carried out. The method used in the present paper consists of covalent bonding of external lysines of the enzyme with a hydrophobic polymer. Enzymes with several degrees of modification have been obtained. These derivatives present different hydrophobic characteristics, depending on the degree of modification. All the modified enzymes are active in hydrophobic solvents such as benzene, toluene or 1,1,1-trichloroethane but need a small amount of water to be activated (< 1.0%). High yields are obtained in the synthesis of peptidic bonds (100% > X > 60%). The modified enzyme has the same stereospecificity as the native enzyme, because only esters with L-configuration in the alpha-carbon are accepted as acyl donors. Nevertheless a greater number of acyl donors are accepted by the modified enzyme than by the native alpha-chymotrypsin, in the synthesis of peptides. On the other hand, the nucleophile subsite is more lipophilic in the modified enzyme than in the native alpha-chymotrypsin.