CYSTEINE PROTEINASE-INHIBITOR FROM PAPAYA (CARICA-PAPAYA L) SEEDS

The protein was isolated from papaya (Carica papaya L.) seeds using affinity chromatography on carboxymethyl-papain. The protein is an effective inhibitor of cysteine proteinase papain and ficin and to a lesser extent of bromelain. Serine, aspartic and metalloproteinases are not inhibited by this protein. The molecular weight of the inhibitor was estimated to be about 43000 by gel filtration on Toyopearl HW-50 and by SDS-polyacrylamide gel electrophoresis. Stoichiometry of the reaction between the inhibitor and proteinases showed that one mole of this inhibitor inhibits one mole of papain and ficin. Amino acid analysis showed that the inhibitor contains six residues of cysteine and is rich in glutamic acid. Two free SH-groups were detected in the inhibitor according to the Ellman procedure.