High level production of bioactive di- and tri-tyrosine peptides by protease-catalyzed reactions.

Papain-catalyzed polymerization of L-tyrosine ethyl ester in aqueous media was efficient for synthesis of oligo-tyrosine peptides having angiotensin I-converting enzyme inhibitory activity. Di-, tri-, and tetra-tyrosine accumulated in the soluble fraction of reaction mixture. On the other hand, the peptide products with degree of polymerization from 5 to 10 were insoluble, yields of which were influenced by initial concentrations of the ester substrate. The precipitated products could be used as substrates for α-chymotrypsin in DMSO/buffer systems producing soluble oligo-tyrosine peptides. In the reaction media containing DMSO at 40-50% (v/v), most of the precipitates were converted to soluble peptides. The two-step enzymatic reaction, that is papain-catalyzed synthesis of Tyr-polymers from L-tyrosine ethyl ester followed by their hydrolytic cleavage by α-chymotrypsin, is expected to be a potent procedure for synthesis of biologically active di- and tri-tyrosine peptides in good yield.