Oligo-tyrosine peptides such as Tyr-Tyr having angiotensin I-converting enzyme (ACE) inhibitory activity could be synthesized by alpha-chymotrypsin-catalyzed reaction With L-tyrosine ethyl ester in aqueous media However. peptide yield in the reaction was below 10%. Since L-tyrosine amide showed highly nucleophilic activity for the deacylation of enzyme through which a new peptide bond was made, its application to the enzymatic peptide synthesis was evaluated in this study Addition of tyrosine amide into the reaction produced Tyr-Tyr-NH2, of which yield exceeded 130% on the basis of tyrosine ethyl ester. Although purified Tyr-Tyr-NH2 did not inhibit ACE activity, alpha-chymotrypsin could act on the dipeptide amide and convert about 40% of it to Tyr-Tyr The use of both ester and amide forms of tyrosine is expected to be a potent procedure for alpha-chymotrypsin-catalysed synthesis of antihypertensive peptides. (C) 2009 Elseviei Inc. All rights reserved.