Several glucosinolates derived from methionine are accumulated by Arabidopsis thaliana (Haughn et al, 1991). The keto acid of methionine (n = 2 in the scheme shown below) can be progressively increased in carbon chain length by a chain extension pathway, and each of these keto acids can then be transaminated to the corresponding amino acid (n = 3 to 8) (Haughn et al, 1991). These side-chains can then be converted to their corresponding sulfoxides with methylsulfinylalkyl side-chains (Haughn et al, 1991). The synthesis of glucosinolates is microsomal (Du and Halkier, 1996).

The mechanism of chain elongation (condensation of a 2-oxo acid with acetyl-CoA to form a 2-malic acid derivative; isomerization to a 3-malate derivative; and oxidative decarboxylation to give a 2-oxo acid elongated by one methylene group) is similar to the sequence of reactions involved in leucine biosynthesis (Graser et al, 2001) (see leucine biosynthesis under Branched chain amino acid and lysine biosynthesis):

The bushy (bus1-1) mutant of Arabidopsis thaliana completely lacks short-chain glucosinolates derived from methionine, and has a mutation in the gene encoding the cytochrome P-450, CYP79F1, that converts short-chain methionine (dihomomethionine and trihomomethionine) to their corresponding aldoximes (Reintanz et al, 2001). This metabolic lesion appears to result in increased levels of indole-3-ylmethyl-glucosinolate, indole-3-acetic acid and indole-2-acetonitrile (Reintanz et al, 2001) (see: glucosinolates derived from aromatic amino acids under Secondary products derived from aromatic amino acids). Transgenic A. thaliana with cosuppression of CYP79F1 have a reduced content of aliphatic glucosinolates, increased levels of dihomomethionine and trihomomethionine, loss of apical dominance and multiple axillary shoots (Hansen et al, 2001).

Du L, Halkier BA 1996 Isolation of a microsomal enzyme system involved in glucosinolate biosynthesis from seedlings of Tropaeolum majus L. Plant Physiol. 111: 831-837.

Glendening TM, Poulton JE 1990 Partial purification and characterization of a 3'-phosphosulfate:desulfoglucosinolate sulfotransferase from cress (Lepidium sativum). Plant Physiol. 94: 811-818.

Graser G, Schneider B, Oldham NJ, Gershenzon J 2000 The methionine chain elongation pathway in the biosynthesis of glucosinolates in Eruca sativa (Brassicaceae). Arch. Biochem. Biophys. 378 :411-419.

Hansen CH, Wittstock U, Olsen CE, Hick AJ, Pickett JA, Halkier BA 2001 Cytochrome p450 CYP79F1 from Arabidopsis catalyzes the conversion of dihomomethionine and trihomomethionine to the corresponding aldoximes in the biosynthesis of aliphatic glucosinolates. J. Biol. Chem. 276: 11078-11085.

Haughn GW, Davin L, Giblin M, Underhill EW 1991 Biochemical genetics of plant secondary metabolites in Arabidposis thaliana. The glucosinolates. Plant Physiol. 97: 217-226.

Reintanz B, Lehnen M, Reichelt M, Gershenzon J, Kowalczyk M, Sandberg G, Godde M, Uhl R, Palme K 2001 bus, a Bushy Arabidopsis cyp79f1 knockout mutant with abolished synthesis of short-chain aliphatic glucosinolates. Plant Cell 13: 351-367.