[Synthesis of leucine- and methionine-enkephalin using papain]

Thiol protease papain has been used for synthesis of leucine-and methionineenkephalin from methyl esters of N-protected amino acids. The synthesis was carried out in basic medium, minimizing the hazard of the secondary peptide hydrolysis. The reaction products remain in solution during the whole process. The yields at the final stage of the synthesis were 89% (leucineenkephalin) and 79% (methionineenkephalin).