Glucobrassicin is a type of

glucosinolate Glucosinolates are natural components of many pungent plants such as mustard, cabbage, and horseradish. The pungency of those plants is due to mustard oils produced from glucosinolates when the plant material is chewed, cut, or otherwise damaged. T ...

that can be found in almost all cruciferous plants, such as

cabbage Cabbage, comprising several cultivars of ''Brassica oleracea'', is a leafy green, red (purple), or white (pale green) biennial plant grown as an annual vegetable crop for its dense-leaved heads. It is descended from the wild cabbage ( ''B.&nb ...

broccoli Broccoli (''Brassica oleracea'' var. ''italica'') is an edible green plant in the cabbage family (family Brassicaceae, genus ''Brassica'') whose large flowering head, stalk and small associated leaves are eaten as a vegetable. Broccoli is cl ...

, mustards, and

woad ''Isatis tinctoria'', also called woad (), dyer's woad, or glastum, is a flowering plant in the family Brassicaceae (the mustard family) with a documented history of use as a blue dye and medicinal plant. Its genus name, Isatis, derives from ...

. As for other glucosinolates, degradation by the

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

myrosinase Myrosinase (, ''thioglucoside glucohydrolase'', ''sinigrinase'', and ''sinigrase'') is a family of enzymes involved in plant defense against herbivores, specifically the mustard oil bomb. The three-dimensional structure has been elucidated and is ...

is expected to produce an

isothiocyanate In organic chemistry, isothiocyanate is the functional group , formed by substituting the oxygen in the isocyanate group with a sulfur. Many natural isothiocyanates from plants are produced by enzymatic conversion of metabolites called glucosinol ...

, indol-3-ylmethylisothiocyanate. However, this specific isothiocyanate is expected to be highly unstable, and has indeed never been detected. The observed hydrolysis products when isolated glucobrassicin is degraded by myrosinase are

indole-3-carbinol Indole-3-carbinol ( C9 H9 N O), sometimes referred to as I3C, is produced by the breakdown of the glucosinolate glucobrassicin, which can be found at relatively high levels in cruciferous vegetables such as broccoli, cabbage, cauliflower, brusse ...

and

thiocyanate ion Thiocyanate (also known as rhodanide) is the anion . It is the conjugate base of thiocyanic acid. Common derivatives include the colourless salts potassium thiocyanate and sodium thiocyanate. Mercury(II) thiocyanate was formerly used in pyrot ...

(plus glucose, sulfate, and hydrogen ion), which are envisioned to result from a rapid reaction of the unstable isothiocyanate with water. However, a large number of other reaction products are known, and indole-3-carbinol is not the dominant degradation product when glucosinolate degradation takes place in crushed plant tissue or in intact plants. Glucobrassicin is also known to be a highly active egg-laying stimulant of cabbage white butterflies such as the small white (''

Pieris rapae ''Pieris rapae'' is a small- to medium-sized butterfly species of the whites-and-yellows family Pieridae. It is known in Europe as the small white, in North America as the cabbage white or cabbage butterfly, on several continents as the small ca ...

'') and the large white (''

Pieris brassicae ''Pieris brassicae'', the large white, also called cabbage butterfly, cabbage white, cabbage moth (erroneously), or in India the large cabbage white, is a butterfly in the family Pieridae. It is a close relative of the small white, ''Pieris ra ...

''). Several

derivatives The derivative of a function is the rate of change of the function's output relative to its input value. Derivative may also refer to: In mathematics and economics * Brzozowski derivative in the theory of formal languages * Formal derivative, an ...

of glucobrassicin are known. The compound itself was first isolated from ''

Brassica ''Brassica'' () is a genus of plants in the cabbage and mustard family (Brassicaceae). The members of the genus are informally known as cruciferous vegetables, cabbages, or mustard plants. Crops from this genus are sometimes called ''cole cr ...

'' plants, hence the ending of the name. When a second, similar natural product was discovered, it was named neoglucobrassicin. When further derivatives were discovered, a more systematic nomenclature was used. Currently, the following six derivatives are known from plants: * 1-Methoxyglucobrassicin (neoglucobrassicin) * 4-Hydroxyglucobrassicin * 4-Methoxyglucobrassicin * 1,4-Dimethoxyglucobrassicin * 1-Sulfoglucobrassicin * 6′-Isoferuloylglucobrassicin The three first mentioned derivatives are as frequent in crucifers as glucobrassicin itself. The additional three derivatives appear to be rare in nature. 4-methoxyglucobrassicin was recently reported to be a signal molecule involved in plant defence against bacteria and fungi.

Biosynthesis from tryptophan

The biosynthesis of glucobrassicin begins with tryptophan produced through several steps from the

shikimic acid pathway The shikimate pathway (shikimic acid pathway) is a seven-step metabolic pathway used by bacteria, archaea, fungi, algae, some protozoans, and plants for the biosynthesis of folates and aromatic amino acids (tryptophan, phenylalanine, and tyrosin ...

compound,

chorismic acid Chorismic acid, more commonly known as its anionic form chorismate, is an important biochemical intermediate in plants and microorganisms. It is a precursor for: * The aromatic amino acids phenylalanine, tryptophan, and tyrosine * Indole, indole d ...

. Tryptophan is converted to indole-3-acetaldoxime (IAOx) by

cytochrome p450 Cytochromes P450 (CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are ...

enzymes (the redundant CYP92B3 and CYP79B3 in ''Arabidopsis thaliana'') using NADPH and molecular Oxygen. A separate p450 enzyme (CYP83B1 in ''Arabidopsis'') catalyzes a second subsequent monooxygenase reaction to create a proposed the intermediate 1-''aci''-nitro-2-indolyl-ethane. A cysteine is utilized by glutathione ''S''-transferase (GST) in a conjugation process to produce an ''S''-alkylthiohydroximate derivative, which is then cleaved off by a carbon–sulfur lyase (like the SUR1 enzyme found in ''Arabidopsis'') to create a free thiol. A single glucosylation occurs attaching a glucose molecule to the indole hydroximate through a thioether linkage. Finally, the hydroximate itself is sulfated creating glucobrassicin. Biosynthesis of Glucobrassicin

References

External links

* {{Glycosides Glucosinolates Indoles

Biosynthesis from tryptophan

See also

References

External links