CARICA-PAPAYA LATEX IS A RICH SOURCE OF A CLASS-II CHITINASE

A class II chitinase is present in the latex of the tropical species C arica papaya. The enzyme may be readily purified by using a combinatio n of hydrophobic interaction-and cation-exchange chromatography. This. enzyme preparation is homogeneous with respect to the three physico-c hemical criteria of charge, M-r (28 000) and hydrophobicity. It is als o completely free of any proteolytic and bacteriolytic activities. The enzyme was classified as a class II chitinase on the basis of its N-t erminal amino acid sequence up to the 30th residue. In agreement with this classification, the enzyme preparation hydrolyses chitinase subst rates only very slowly and several free thiol functions are present in the polypeptide chain. These free thiol functions are buried, and to be available for titration with 2,2'-dipyridyldisulphide, the enzyme m ust be denatured. Unfolding of papaya chitinase requires particularly drastic conditions, not less than 4 M guanidinium hydrochloride at 25 degrees and pH 6.8. (C) 1997 Elsevier Science Ltd.