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

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. Verissimo, 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.