ORGANIC-REACTIONS CATALYZED BY INSOLUBILIZED ENZYMES .3. SYNTHESIS OFPEPTIDES CATALYZED BY ALPHA-CHYMOTRYPSIN IMMOBILIZED ON GRAFT-COPOLYMERS

alpha-Chymotrypsin (alpha-CT) has been covalently immobilized on polye thylene/2-hydroxyethyl methacrylate (PE/HEMA) graft copolymers, with l oadings of 33-87 mg of immobilized protein/g copolymer. These enzymati c derivatives have been used in the kinetically controlled synthesis o f dipeptides. The influence of the enzymatic loading, grafting and hyd rolysis degree of the supports on the synthesis of the model dipeptide Bz-L-Tyr-L-Leu-NH2 is discussed. Organic solvents with different log P values mixed in different proportions with an aqueous buffer have be en used as reaction media The best yields with respect to peptide synt hesis are obtained with ethyl acetate/buffer pH= 9.0 (2/1 v/v)). H-L-L eu-NH2 seems to be a better nucleophile than H-L-Ala-NH2, and Bz-L-Tyr -OEt seems to be a better acyl donor than Ac-L-Phe-OMe under the optim al experimental conditions.