Glucosinolate

  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, furthermore Capparidaceae and Caricaceae), but also in the genus Dryetes (family Euphorbiaceae)[1]. 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, radish, horseradish, cress, cabbage, Brussels sprouts, kohlrabi, kale, cauliflower, broccoli, turnip, swede and rapeseed.

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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: So called aliphatic glucosinolates derived from mainly methionine, but also alanine, leucine, or valin. Indolic glucosinolates are derived from tryptophan, while aromatic ones come mainly from phenylalanine, but also tyrosine. 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). The glucosinolate sinigrin amongst others was shown to be responsible for the bitterness of cooked cauliflower [2] as well as in Brussels sprouts [3]. 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).

Glucosinolates are well known for their toxic effects (mainly as goitrogens) in both man and animals at high doses. In contrast at subtoxic doses, their hydrolytic and metabolic products act as chemoprotective agents against chemically-induced carcinogens by blocking the initiation of tumors in a variety of rodent tissues, viz. liver, colon, mammary gland, pancreas, etc. They exhibit their effect by inducing Phase I and Phase II enzymes, inhibiting the enzyme activation, modifying the steroid hormone metabolism and protecting against oxidative damages.[4]

Glucosinolates are synonymous to 'Mustard oil glycosides' and 'Thioglucosides'.

See also

• Sinigrin
• Sinalbin
• Gluconasturtiin
• Glucobrassicin

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
• Reintanz B et al.: Molecules, Morphology, and Dahlgren's Expanded Order Capparales
• Srinibas Das, Amrish Kumar Tyagi and Harjit Kaur: Cancer modulation by glucosinolates: A review