Chemoselectivity of chemically modified α-chymotrypsin

Article abstract of DOI:10.1016/0040-4020(94)01060-D

The enzymatic activity of α-chymotrypsin chemically modified with monomethoxypolyethylene glycol (α-CT-PEG) is discussed using as test reactions the hydrolysis of esters different from the natural substrates of the enzyme, and the peptidic synthesis. These reactions allowed the analysis of the dimensions of 'ar', 'h', 'n' and 'am' subsites of α-CT-PEG. Using 2-aminoethanol esters and derivatives of glycine we have proved that the depth of the 'n' subsite of the chemically modified α-CT (α-CT-PEG) must be lower than 14.455 A because the synthesis of peptides is not observed using 2-aminoethanol octanoate as nucleophile. α-CT-PEG is chemoselective towards the aromatic esters because unnatural aliphatic esters are not hydrolyzed in the presence of N-benzoyl-L-Tyrosine ethyl ester. Unnatural aliphatic acyl-donors with a distance H-C......C=O smaller than 8.8 A are recognized by the chemically modified enzyme as acyl-donors. From these results we can conclude that the presence of N-acyl group in the acyl-donor molecule is not necessary to be recognised by α-CT-PEG. The presence of bulky alkyl chain both in the acyl donor and in the nucleophile, reduces the enzymatic activity of the biocatalysts both in the hydrolysis of esters and in the synthesis of peptides.