A 7.5-kD Inhibitor of Cysteine Proteinases from Pumpkin Seeds

E. V. Ievleva,^1,2 Yu. A. Rudenskaya,¹ Ya. E. Dunaevsky,³ and V. V. Mosolov¹

¹Bakh Institute of Biochemistry, Russian Academy of Sciences, Leninskii pr. 33, Moscow, 117071 Russia; fax: (7-095) 954-27-32; E-mail: inbio@glas.apc.org

²To whom correspondence should be addressed.

³Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (7-095) 939-31-81.

Submitted December 23, 1996; revision submitted January 29, 1997.

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A 7.5-kD inhibitor of cysteine proteinases has been isolated from pumpkin seeds (Cucurbita maxima L.). The purification procedure includes affinity 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 inhibitor contains no cysteine. The N-terminal amino acid sequence of the inhibitor was determined. The isolated inhibitor is highly effective against ficin (K_i = 1.06·10^-7 M) and papain (K_i = 1.15·10^-7 M), is less effective against chymopapain, and had no activity against bromelain. In spite of the significantly lower molecular mass, the other properties of the inhibitor are similar to other cystatins from plants.

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KEY WORDS: bromelain, proteinase inhibitor, cystatin, ficin, papain, pumpkin.

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