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Characterization of an Aminopeptidase from Grapes
Han‐Chul Kang, Tae‐Ryong Hahn, In‐Sik Chung and Jong‐Cheon Park
International Journal of Plant Sciences
Vol. 160, No. 2 (March 1999), pp. 299-306
Published by: The University of Chicago Press
Stable URL: http://www.jstor.org/stable/10.1086/314132
Page Count: 8
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The aminopeptidase activities from grapes, Vitis labruscana B. Takasumi, increased parallel to the developmental stages and were, in order of activity, high for Phe‐, Leu‐, and Met‐p‐nitroanilides (aminoacyl‐NAs). The activities were concentrated in the hypodermis from fully ripe grapes rather than in the flesh (mesocarp and placental tissue) or seeds. The rapid hydrolysis of the substrates was a common characteristic of the hypodermis of other strains, indicating that Phe‐specific aminopeptidase may play an important role in the hypodermis. An aminopeptidase was purified over 130‐fold from the hypodermis. The enzyme is a monomer of ca. 71–74 kDa as determined by SDS‐PAGE and Sephacryl S‐200 chromatography. The purified aminopeptidase, as well the crude extracts from whole grape and hypodermis, hydrolyzed aminoacyl‐NAs with nonpolar side chains such as Phe and Leu more efficiently. The order of activity was similar to the crude extract of the hypodermis, indicating that the enzyme may be a major aminopeptidase in the hypodermis. The enzyme had a pH optimum of 7.0. The increase of activity up to pH 7.0 seems to be correlated with the increase in pH in the hypodermis during ripening. N‐terminal‐blocked Phe‐ and some oligopeptidyl‐NAs as well as azocasein were not hydrolyzed. Phenylmethylsulfonyl fluoride and N‐ethylmaleimide inhibited the enzyme in concentration‐ and time‐dependent manners. To some extent, aprotinin selectively decreased the activity. The enzyme was neither significantly influenced by some metal ions nor inhibited by EDTA or 1,10‐phenanthroline.
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