MetaCyc Pathway: superpathway of Allium flavor precursors
Inferred from experiment

Pathway diagram: superpathway of Allium flavor precursors

If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.

Superclasses: BiosynthesisSecondary Metabolites BiosynthesisSulfur-Containing Secondary Compounds Biosynthesis

Some taxa known to possess this pathway include : Allium aflatunense, Allium altaicum, Allium ampeloprasum, Allium cepa, Allium sativum, Allium tuberosum

Expected Taxonomic Range: Allioideae, cellular organisms

Plants belonging to the Allioideae family have been valued both for flavor and medicinal purposes throughout the world. The domestic Alliums (such as onion, garlic, chives and leek) contain high concentrations of organic sulfur compounds especially in their bulbs and leaves. These compounds consist mostly of S-alkyl-L-cysteine S-oxides such as alliin, (+)-trans-isoalliin, and methiin, as well as γ-glutamyl peptides (together these compounds make up over 70% of the total sulfur in garlic [Lawson96]).

These compounds, which are found in the cytoplasm, are produced constitutively. The S-alkyl cysteine S-oxides are substrates for the alliinase enzymes ( EC, alliin lyase), which convert them to S-alkylsulfenates. However, the enzymes are kept in vacuoles, and are thus sequestered from their substrates [Lancaster81, Pickering09]. Only when the tissue is injured, the alliinase enzymes are released from the vaculoes and interact with their substrates, producing S-alkylsulfenates. [Rose05]. Once formed, S-alkylsulfenates are very active and tend to condense spontaneously, forming thiosulfinates [Aoyagi11]. Depending on the Allium species, and under differing conditions, the thiosulfinates can decompose to form additional sulfur constituents including diallyl, methyl allyl, and diethyl mono-, di-, tri-, tetra-, penta-, and hexasulfides, vinyldithiins, and (E)- and (Z)-ajoene [Rose05].

In some species, dedicated enzymes commonly known as "lachrymatory-factor synthases" act on the S-alkylsulfenates rapidly, before they condense, producing volatile compounds that cause the eyes of animals to tear (lachrymatory factors) - a further defense mechanism against herbivory.

Subpathways: alliin metabolism, ethiin metabolism, propanethial S-oxide biosynthesis

Created 24-Mar-2009 by Pujar A, Boyce Thompson Institute
Revised 10-Dec-2014 by Caspi R, SRI International


Aoyagi11: Aoyagi M, Kamoi T, Kato M, Sasako H, Tsuge N, Imai S (2011). "Structure and bioactivity of thiosulfinates resulting from suppression of lachrymatory factor synthase in onion." J Agric Food Chem 59(20);10893-900. PMID: 21905712

Lancaster81: Lancaster JE, Collin HA (1981). "Presence of alliinase in isolated vacuoles and of alkyl cysteine sulphoxides in the cytoplasm of bulbs of onion (Allium cepa)." Plant Science Letters 22(2);169-176.

Lawson96: Lawson, L.D. (1996). "The composition and chemistry of garlic cloves and processed garlic." in H.P. Koch, L.D. Lawson (Eds.), Garlic: The Science and Therapeutic Application of Allium sativum L. and Related Species (second ed.), Williams and Wilkins, Baltimore, USA. pp. 37-108.

Manabe98: Manabe T, Hasumi A, Sugiyama M, Yamazaki M, Saito K (1998). "Alliinase [S-alk(en)yl-L-cysteine sulfoxide lyase] from Allium tuberosum (Chinese chive)--purification, localization, cDNA cloning and heterologous functional expression." Eur J Biochem 257(1);21-30. PMID: 9799098

Pickering09: Pickering IJ, Sneeden EY, Prince RC, Block E, Harris HH, Hirsch G, George GN (2009). "Localizing the chemical forms of sulfur in vivo using X-ray fluorescence spectroscopic imaging: application to onion (Allium cepa) tissues." Biochemistry 48(29);6846-53. PMID: 19463015

Rose05: Rose P, Whiteman M, Moore PK, Zhu YZ (2005). "Bioactive S-alk(en)yl cysteine sulfoxide metabolites in the genus Allium: the chemistry of potential therapeutic agents." Nat Prod Rep 22(3);351-68. PMID: 16010345

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

Borlinghaus14: Borlinghaus J, Albrecht F, Gruhlke MC, Nwachukwu ID, Slusarenko AJ (2014). "Allicin: chemistry and biological properties." Molecules 19(8);12591-618. PMID: 25153873

Brodnitz71: Brodnitz MH, Pascale JV (1971). "Thiopropanal S-oxide: a lachrymatory factor in onions." J Agric Food Chem 19(2);269-72. PMID: 5546155

Carson66: Carson J F, Lundin R E, Lukes TM (1966). "The Configuration of (+)-S-(1-Propenyl)-L-Cysteine S-Oxide from Allium cepa." The Journal of Organic Chemistry 31(5);1634-1635.

Eady08: Eady CC, Kamoi T, Kato M, Porter NG, Davis S, Shaw M, Kamoi A, Imai S (2008). "Silencing onion lachrymatory factor synthase causes a significant change in the sulfur secondary metabolite profile." Plant Physiol 147(4);2096-106. PMID: 18583530

Edwards97: Edwards S. J., Britton G., Collin H. A. (1997). "The biosynthetic pathway of the S-alk(en)yl-L-cysteine sulphoxides (flavour precursors) in species of Alium." Plant Cell, Tissue and Organ Culture 38:181-188.

Ellmore94: Ellmore, G.S, Feldberg, R.S (1994). "Alliin lyase localization in bundle sheaths of the garlic clove (Allium sativum)." American Journal of Botany, 81, 89-94.

Granroth70: Granroth B. (1970). "Biosynthesis and decomposition of cysteine derivatives in onion and other Allium species." Annales Academiae Scientiarum Fennicae A 154:1-71.

Horhammer68: Horhammer L, Wagner H, Seitz M, Vejdelek ZJ (1968). "[On determination of the value of garlic preparations. 1. Chromatographic studies on the genuine contents of Allium sativum L]." Pharmazie 23(8);462-7. PMID: 5715558

Hughes05: Hughes J, Tregova A, Tomsett AB, Jones MG, Cosstick R, Collin HA (2005). "Synthesis of the flavour precursor, alliin, in garlic tissue cultures." Phytochemistry 66(2);187-94. PMID: 15652575

Imai02: Imai S, Tsuge N, Tomotake M, Nagatome Y, Sawada H, Nagata T, Kumagai H (2002). "Plant biochemistry: an onion enzyme that makes the eyes water." Nature 419(6908);685. PMID: 12384686

Jones04: Jones MG, Hughes J, Tregova A, Milne J, Tomsett AB, Collin HA (2004). "Biosynthesis of the flavour precursors of onion and garlic." J Exp Bot 55(404);1903-18. PMID: 15234988

Kubec00: Kubec R, Svobodova M, Velisek J (2000). "Distribution of S-Alk(en)ylcysteine sulfoxides in some Allium species. Identification Of a new flavor precursor: S-ethylcysteine sulfoxide (Ethiin)." J Agric Food Chem 48(2);428-33. PMID: 10691652

Lancaster00a: Lancaster JE, Shaw ML, Joyce MD, McCallum JA, McManus MT (2000). "A novel alliinase from onion roots. Biochemical characterization and cDNA cloning." Plant Physiol 122(4);1269-79. PMID: 10759524

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

Norris90: Norris PG, Nunn AV, Hawk JL, Cox TM (1990). "Genetic heterogeneity in erythropoietic protoporphyria: a study of the enzymatic defect in nine affected families." J Invest Dermatol 95(3);260-3. PMID: 2384686

Ohsumi93: Ohsumi, C, Hayashi, T, Sano, K (1993). "Formation of alliin in the culture tissues of Allium sativum. oxidation of S-Allyl-L-Cysteine." Phytochemistry, 33,1,107-111.

Prince97: Prince CL, Shuler ML, Yamada Y (1997). "Altering Flavor Profiles in Onion (Allium cepa L.) Root Cultures Through Directed Biosynthesis." Biotechnology Progress 13(4);506-510.

Rabinkov94: Rabinkov A, Zhu XZ, Grafi G, Galili G, Mirelman D (1994). "Alliin lyase (Alliinase) from garlic (Allium sativum). Biochemical characterization and cDNA cloning." Appl Biochem Biotechnol 48(3);149-71. PMID: 7979352

Rubio06: Rubio S, Larson TR, Gonzalez-Guzman M, Alejandro S, Graham IA, Serrano R, Rodriguez PL (2006). "An Arabidopsis mutant impaired in coenzyme A biosynthesis is sugar dependent for seedling establishment." Plant Physiol 140(3);830-43. PMID: 16415216

Selby80: Selby, C, Turnbull, A, Collin, H. A (1980). "Comparison of the onion plant (Allium cepa) and onion tissue culture. II. Stimultaion of flavour precursor synthesis in onion tissue cultures." New Phytol. 84, 307-312.

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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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