Cardosins A and B, two new enzymes available for peptide synthesis

Abstract

Two new aspartic proteases, Cardosins A and B, with a high specificity toward bonds between hydrophobic amino acids were isolated from the flowers of the cardoon, Cynara cardunculus L., and recently characterised [C.J. Faro, A.G.J. Moir, E. Pires, Biotech. Lett., 14 (1992) 841.]; [P. Verı́ssimo, C. Faro, A.J.G. Moir, Y. Lin, J. Tang, E. Pires, Eur. J. Biochem., 235 (1996) 762.]. Cardosins were shown to be stable in aqueous–organic biphasic systems [M. Barros, M.G.V. Carvalho, F.A. Garcia, E. Pires, Biotech. Lett. 14 (1992) 174.]. In this work, we have investigated peptide bond specificity of Cardosin A and Cardosin B in what concerns the amino acids in P′1 position. The results were compared with pepsin under the same conditions. Information about secondary specificity of Cardosin A and B was also investigated by tripeptide synthesis. The condensation reactions were carried out in aqueous–organic biphasic systems of n-hexane/ethyl acetate and sodium phosphate buffer. The reaction products were isolated by RP-HPLC and identified by amino acid analysis and eventually by M.S. The results in the synthesis of dipeptides showed that Cardosin A and B have similar P′1 position preference. The production of tripeptides by condensation of CBZ·Val·Phe with Phe·OMe, Met·OMe and Val·OMe reveals that the addition of Val in the P2 position modifies the Cardosins' preferences concerning the amino acid in P′1 position.