ACC can be conjugated to 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC). MACC synthesis is catalyzed by ACC N-malonyltransferase (Yang, 1989; Martin and Saftner, 1995; Chick and Leung, 1997). An alternative ACC conjugate has been identified in tomato fruits: 1-(gamma-glutamylamino)cyclopropane-1-carboxylic acid (GACC) (Martin et al, 1995). However, Peiser and Yang (1998) show that the GACC is only formed in mature-green tomato fruit in an amount only 10% of that of MACC. MACC (and GACC) formation may contribute to the regulation of ACC levels and hence ethylene formation (Yang, 1989; Kende, 1993; Banga et al, 1996).

Banga M, Slaa EJ, Blom CWPM, Voesenek LACJ 1996 Ethylene biosynthesis and accumulation under drained and submerged conditions: a comparative study of two Rumex species. Plant Physiol. 112: 229-237.

Chick WSH, Leung PC 1997 Immunopurification and characterization of a 40-kD 1-aminocyclopropane-1-carboxylic acid N-malonyltransferase from mung bean seedling hypocotyls. Plant Physiol. 113: 119-126.

Kende H 1993 Ethylene biosynthesis. Annu. Rev. Plant Physiol. Plant Mol. Biol. 44: 283-307.

Martin MN, Cohen JD, Saftner RA 1995 A new 1-aminocyclopropane-1-carboxylic acid-conjugating activity in tomato fruit. Plant Physiol. 109: 917-926.

Martin MN, Saftner RA 1995 Purification and characterization of 1-aminocyclopropane-1-carboxylic acid N-malonyltransferase from tomato fruit. Plant Physiol. 108: 1241-1249.

Peiser G, Yang SF 1998 Evidence for 1-(malonylamino)cyclopropane-1-carboxylic acid being the major conjugate of aminocyclopropane-1-carboxylic acid in tomato fruit. Plant Physiol. 116: 1527-1532.

Yang SF 1989 Metabolism of 1-aminocyclopropane-1-carboxylic acid in relation to ethylene biosynthesis. In "Plant Nitrogen Metabolism" (JE Poulton, JT Romeo, EE Conn eds), Rec. Adv. Phytochem., Vol. 23, Plenum Press, New York, pp. 263-287.