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The glucosinolates are a class of organic compounds that contain sulfur, nitrogen and a group derived from glucose. They occur as secondary metabolites of many plants of the order Brassicales (especially in the family Brassicaceae). Plants use substances derived from glucosinolates as natural pesticides and as defense against herbivores; these substances are also responsible for the bitter or sharp taste of many common foods such as mustard, horseradish, cabbage and Brussels sprouts.
Glucosinolates are water-soluble anions and belong to the glucosides. Every glucosinolate contains a central carbon atom which is bond via a sulfur atom to the glycone group, and via a nitrogen atom to a sulfonated oxime group. In addition, the central carbon is bond to a side group; different glucosinolates have different side groups.
About 120 different glucosinolates are known to occur naturally in plants. They are synthesized from certain amino acids: methionine, phenylalanine, tyrosine or tryptophan. The plants contain the enzyme myrosinase which, in the presence of water, cleaves off the glucose group from a glucosinolate. The remaining molecule then quickly converts to a thiocyanate, an isothiocyanate or a nitrile; these are the active substances that serve as defense for the plant. To prevent damage to the plant itself, the myrosinase and glucosinolates are stored in separate compartments of the cell and come together only under conditions of stress or injury.
Because the use of glucosinolate-containing crops as primary food source for animals was shown to have negative effects, food crops have been developed that contain very low amounts of glucosinolates (e.g. canola). On the other hand, plants producing large amounts of glucosinolates are also desirable, because substances derived from these can serve as natural pesticides and are under investigation in the prevention of cancer (with sulforaphane in broccoli being the best known example).
References
- Bones AM, Rossiter JT: The myrosinase-glucosinolate system - an innate defense system in plants, Physiologia plantarum 97 (1): pages 194-208, May 1996
- Abel S: Glucosinolates and Chemoprevention of Cancer
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