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ARS Home » Research » Publications at this Location » Publication #61893
Title: A NEW 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID-CONJUGATING ACTIVITY IN TOMATO FRUIT

Author
item MARTIN, MELINDA - 1275-49-00
item Cohen, Jerry
item Saftner, Robert

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: The plant hormone, ethylene, plays a major role in the ripening and postharvest quality of tomato fruit. By controlling the time and amount of ethylene produced in the fruit, we can control the ripening and delay the onset of over ripening and spoilage. One important control point in ethylene biosynthesis is the availability of ACC, the immediate precursor of ethylene. We have purified and characterized a new enzyme that diverts ACC away from ethylene synthesis, have definitively identified the product of this enzyme's activity and have shown how the enzyme's activity changes during ripening in various parts of the fruit. This information will help in developing strategies to modify the enzyme's activity to enhance or delay the ripening process as desired. These results will benefit plant scientists in the fruit industry who are interested in controlling the quality of fruit delivered to the consumer.

Technical Abstract: A new conjugate (GACC) of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is identified. The only previously identified conjugate of ACC is 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC). GACC, not MACC, was the major conjugate formed by crude protein extracts of tomato fruit pericarp and seeds incubated with [14C]ACC. GACC was resolved from [14C]AC and [14C]MACC by reverse phase C18 thin-layer chromatography and subsequently detected and quantified using a radioisotope imaging system. Proteins precipitated from crude extracts failed to catalyze formation of GACC unless the supernatant was added back. Reduced glutathione, but not other reducing agents, replaced the crude supernatant. When [35S-cys]glutathione and [3H-2gly]glutathione were employed as substrates, neither radiolabled glycine nor cysteine from the glutathione tripeptide were incorporated into GACC. Oxidized glutathione, S-substituted glutathione, and di- and tripeptides having an N-terminal y-L-glutamic acid, but lacking cysteine and glycine, also served as substrates for GACC formation. Peptides lacking the N-terminal y-L-glutamic acid dod not serve as substrates. Acid hydrolysis of GACC yielded ACC suggesting that GACC is an amide-linked conjugate of ACC. Taken together, these results indicate that GACC is 1-(y-glutamylamino)cyclopropane-1-carboxylic acid and that its formation is catalyzed by a y-glutamyltranspeptidase. GC-MS analysis of the N-acetyl dimethyl ester of GACC confirmed this structure.