Purification and characterization of a cysteine endopeptidase from Vasconcellea quercifolia A. St.-Hil. latex displaying high substrate specificity.

A new proteolytic preparation from Vasconcellea quercifolia ("oak leaved papaya") latex containing several cysteine endopeptidases with high proteolytic activity has been obtained. The specific activity of the new enzymatic preparation (VQ) was higher than that of Carica papaya latex. VQ was able to coagulate milk and to hydrolyze caseins and then could be used to produce cheeses and/or casein hydrolysates. Ion exchange chromatography of VQ allowed the isolation of a new protease, named quercifoliain I, homogeneous when analyzed by SDS-PAGE, IEF and MALDI-TOF-MS. Molecular mass was 24195 Da, and its isoelectric point was >9.3. The N-terminal sequence was determined (YPESVDWRQ). Insulin B-chain cleavage showed higher specificity than that of papain and was restricted to glycyl and alanyl residues at P1' position. The tryptic peptide mass fingerprint of quercifoliain I analyzed with the MASCOT search tool did not find a match with papain or any other plant cysteine proteases.