A 7.5-KD INHIBITOR OF CYSTEINE PROTEINASES FROM PUMPKIN SEEDS

A 7.5-kD inhibitor of cysteine proteinases has been isolated from pump kin seeds (Cucurbita maxima L.). The purification procedure includes a ffinity chromatography on ficin-Sepharose and HPLC on Superose-6. The molecular mass of the inhibitor is 7.5 kD and its pi is 6.0. The inhib itor contains no cysteine. The N-terminal amino acid sequence of the i nhibitor was determined. The isolated inhibitor is highly effective ag ainst ficin (K-i = 1.06.10-(7) M) and papain (K-i = 1.15.10(-7) M), is less effective against chymopapain, and has no activity against brome lain. In spite of the significantly lower molecular mass, the other pr operties of the inhibitor are similar to those of other cystatins from plants.