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MetaCyc Pathway: sulfur volatiles biosynthesis
Inferred from experiment

Enzyme View:

Pathway diagram: sulfur volatiles biosynthesis

This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.

Synonyms: biosynthesis of sulphur volatiles

Superclasses: Degradation/Utilization/AssimilationInorganic Nutrients MetabolismSulfur Compounds Metabolism
Metabolic Clusters

Some taxa known to possess this pathway include : Arabidopsis thaliana col, Brassica oleracea

Expected Taxonomic Range: Brassicaceae

Glucosinolates are substituted β-thioglucoside N-hydroxysulfates, formed by certain plants from any one of eight amino acids, namely, alanine, valine, leucine, isoleucine, phenylalanine, methionine, tyrosine and tryptophan. Over 115 naturally occurring glucosinolates have been identified [Hayes08]. Much of the diversity amongst glucosinolates arises from the addition of different sized alkyl groups to the side chain of the amino acids, principally valine, phenylalanine and methionine.

Glucosinolates are found prominently in the order Brassicaceae, which includes cabbage, mustard, oilseed rape, broccoli, and the model plant Arabidopsis, and are responsible for the typical sharp taste and odor of these plants.

The glucosinolates are hydrolyzed by the plant to compounds that are toxic to herbivores, and play an important role in plant defense. The hydrolysis of is catalyzed by myrosinases (b-thioglucoside glucohydrolase, EC ), enzymes that are physically segregated from glucosinolates within the intact plant in specialized ''myrosin'' cells, and are brought into contact by tissue damage [Bones96].

The products of the myrosinase reaction are unstable aglycons, thiohydroximate-O-sulfates, that decompose to different types of products, depending on the chemical nature of the side chain of the parent glucosinolate and the conditions of hydrolysis. Products include nitriles, isothiocyanates, thiocyanates, oxazolidine-2-thiones, and epithionitriles.

Glucosinolates with an aliphatic side chain are generally hydrolyzed to yield isothiocyanates at a neutral pH. However, acidic pH or the presence of Fe2+ ions favors the production of nitriles [Gil80].

In some plants, additional proteins are involved in glucosinolate hydrolysis. For example, it has been shown that the presence of an epithiospecifier protein (ESP) results in conversion of thiohydroximate-O-sulfates to bioactive nitriles or epithionitriles [Lambrix01]. If the parent glucosinolate possessed a terminal alkene group, epithionitriles are formed (by transfer of the sulfur atom from the basic glucosinolate backbone to the terminal alkene residue of the side chain), whereas other glucosinolates are converted to simple nitriles. The protein appears to have no catalytic activity in the absence of myrosinase [Daxenbichler68, Tookey73, MacLeod85, Lambrix01, Zabala05]. In the absence of ESP, as in some Capparales species, isothiocynates are the only breakdown products [Lambrix01].

About this pathway : The hydrolysis products of glucosinolates are methylated to volatile sulfur compounds by five distinct isoforms of thiol methyltransferases (TMT) in Brassica oleracea. The produced sulfur volatiles play a role in anti-insect and anti-pathogen activities. The expression pattern of TMT's in cabbage correlated with the glucosinolate accumulation. These TMT's possess the methyltransferase signature in their sequence but had distinct functions from them [Attieh02].

Created 25-Feb-2011 by Pujar A, Boyce Thompson Institute


Attieh02: Attieh J, Djiana R, Koonjul P, Etienne C, Sparace SA, Saini HS (2002). "Cloning and functional expression of two plant thiol methyltransferases: a new class of enzymes involved in the biosynthesis of sulfur volatiles." Plant Mol Biol 50(3);511-21. PMID: 12369626

Bones96: Bones, A.M., Rossiter, J.T. (1996). "The myrosinase-glucosinolate system, its organisation and biochemistry." Physiol. Plant. 97:194-208.

Daxenbichler68: Daxenbichler, M.E., VanEtten, C.H., Wolff, I.A. (1968). "Diastereomeric episulfides from epi-progoitrin upon autolysis of crambe seed meal." Phytochemistry 7:989-996.

Gil80: Gil, V., MacLeod, A.J. (1980). "The effects of pH on glucosinolate degradation by a thioglucoside glucohydrolase preparation." Phytochemistry 19:2547-2551.

Hayes08: Hayes JD, Kelleher MO, Eggleston IM (2008). "The cancer chemopreventive actions of phytochemicals derived from glucosinolates." Eur J Nutr 47 Suppl 2;73-88. PMID: 18458837

Lambrix01: Lambrix V, Reichelt M, Mitchell-Olds T, Kliebenstein DJ, Gershenzon J (2001). "The Arabidopsis epithiospecifier protein promotes the hydrolysis of glucosinolates to nitriles and influences Trichoplusia ni herbivory." Plant Cell 13(12);2793-807. PMID: 11752388

MacLeod85: MacLeod, A.J., Rossiter, J.T. (1985). "The occurrence and activity of epithiospecifier protein in some Cruciferae seeds." Phytochemistry 24:1895-1898.

Tookey73: Tookey HL (1973). "Crambe thioglucoside glucohydrolase (EC separation of a protein required for epithiobutane formation." Can J Biochem 51(12);1654-60. PMID: 4130022

Zabala05: Zabala Mde T, Grant M, Bones AM, Bennett R, Lim YS, Kissen R, Rossiter JT (2005). "Characterisation of recombinant epithiospecifier protein and its over-expression in Arabidopsis thaliana." Phytochemistry 66(8);859-67. PMID: 15845404

Other References Related to Enzymes, Genes, Subpathways, and Substrates of this Pathway

Attieh00: Attieh J, Sparace SA, Saini HS (2000). "Purification and properties of multiple isoforms of a novel thiol methyltransferase involved in the production of volatile sulfur compounds from Brassica oleracea." Arch Biochem Biophys 380(2);257-66. PMID: 10933880

BrazierHicks08: Brazier-Hicks M, Evans KM, Cunningham OD, Hodgson DR, Steel PG, Edwards R (2008). "Catabolism of glutathione conjugates in Arabidopsis thaliana. Role in metabolic reactivation of the herbicide safener fenclorim." J Biol Chem 283(30);21102-12. PMID: 18522943

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

Zhao12: Zhao N, Ferrer JL, Moon HS, Kapteyn J, Zhuang X, Hasebe M, Neal Stewart C, Gang DR, Chen F (2012). "A SABATH Methyltransferase from the moss Physcomitrella patens catalyzes S-methylation of thiols and has a role in detoxification." Phytochemistry 81;31-41. PMID: 22795762

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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