A NEW 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID-CONJUGATING ACTIVITY IN TOMATO FRUIT

A new conjugate, 1-(gamma-L-glutamylamino)cyclopropane-1-carboxylic ac id (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, no t MACC, was the major conjugate formed by crude protein extracts of to mato (Lycopersicon escolentum Mill cv Ailsa Craig) fruit pericarp and seeds incubated with [C-14]ACC. GACC was resolved from [C-14]ACC and [ C-14]MACC by reversed-phase C-18 thin-layer chromatography and subsequ ently detected and quantified using a radioisotope-imaging system. Pro teins 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 [S-35- cysteine]glutathione and [H-3-2-glycine]glutathione were used as subst rates, neither radiolabeled glycine nor cysteine from the glutathione tripeptide was incorporated into GACC. Oxidized glutathione, S-substit uted glutathione, and di- and tripeptides having an N-terminal gamma-L -glutamic acid, but lacking cysteine and glycine, also served as subst rates for GACC formation. Peptides lacking the N-terminal gamma-L-glut amic acid did 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-(gamma-glutamylamino)c yclopropane-1-carboxylic acid and that its formation is catalyzed by a gamma-glutamyltranspeptidase. Cas chromatography-mass spectrometry an alysis of the N-acetyl dimethyl ester of GACC confirmed this structure .