Glucosinolate
Encyclopedia
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
s that contain sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
and nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and are derived from glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
and an amino acid. They occur as secondary metabolite
Secondary metabolite
Secondary metabolites are organic compounds that are not directly involved in the normal growth, development, or reproduction of an organism. Unlike primary metabolites, absence of secondary metabolities does not result in immediate death, but rather in long-term impairment of the organism's...
s of almost all plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s of the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Brassicales
Brassicales
The Brassicales are an order of flowering plants, belonging to the eurosids II group of dicotyledons under the APG II system. One character common to many members of the order is the production of glucosinolate compounds...
(including the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Brassicaceae
Brassicaceae
Brassicaceae, a medium sized and economically important family of flowering plants , are informally known as the mustards, mustard flowers, the crucifers or the cabbage family....
, Capparidaceae and Caricaceae
Caricaceae
Caricaceae are a family of flowering plants in the order Brassicales, native to tropical regions of Central and South America and Africa. They are short-lived evergreen pachycaul shrubs or small trees growing to 5-10 m tall...
), but also in the genus Drypetes
Drypetes
Drypetes is a plant genus of the family Putranjivaceae. It was previously put in family Euphorbiaceae, tribe Drypeteae and was the sole pantropical zoochorous genus of the family...
(family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Euphorbiaceae
Euphorbiaceae
Euphorbiaceae, the Spurge family are a large family of flowering plants with 300 genera and around 7,500 species. Most are herbs, but some, especially in the tropics, are also shrubs or trees. Some are succulent and resemble cacti....
).
Chemistry
Glucosinolates are water-soluble anions and belong to the glucosideGlucoside
A glucoside is a glycoside that is derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes....
s. Every glucosinolate contains a central carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
atom, which is bound via a sulfur atom to the thioglucose group (making a sulfated ketoxime) and via a nitrogen atom to a sulfate group. In addition, the central carbon is bound to a side group; different glucosinolates have different side groups, and it is variation in the side group that is responsible for the variation in the biological activities of these plant compounds.
Natural diversity from a few amino acids
About 120 different glucosinolates are known to occur naturally in plants. They are synthesized from certain amino acidAmino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s: So-called aliphatic glucosinolates derived from mainly methionine
Methionine
Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein...
, but also alanine
Alanine
Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 amino acids encoded by the genetic code. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...
, leucine
Leucine
Leucine is a branched-chain α-amino acid with the chemical formula HO2CCHCH2CH2. Leucine is classified as a hydrophobic amino acid due to its aliphatic isobutyl side chain. It is encoded by six codons and is a major component of the subunits in ferritin, astacin and other 'buffer' proteins...
, isoleucine
Isoleucine
Isoleucine is an α-amino acid with the chemical formula HO2CCHCHCH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested. Its codons are AUU, AUC and AUA....
, or valine
Valine
Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...
. (Most glucosinolates are actually derived from chain-elongated homologues of these amino acids, e.g. glucoraphanin is derived from dihomomethionine, which is methionine chain-elongated twice). Aromatic glucosinolates include indolic glucosinolates, such as glucobrassicin
Glucobrassicin
Glucobrassicin is a type of glucosinolate that can be found in almost all cruciferous plants, such as cabbages , mustards, cress, and woad. As for other glucosinolates, degradation by the enzyme myrosinase is expected to produce an isothiocyanate, indol-3-ylmethylisothiocyanate...
, derived from tryptophan
Tryptophan
Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...
and others from phenylalanine
Phenylalanine
Phenylalanine is an α-amino acid with the formula C6H5CH2CHCOOH. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. L-Phenylalanine is an electrically neutral amino acid, one of the twenty common amino acids used to biochemically form...
, its chain-elongated homologue homophenylalanine, and sinalbin
Sinalbin
Sinalbin is a glucosinolate found in the seeds of white mustard, Sinapis alba, and in many wild plant species. In contrast to mustard from black mustard seeds which contain sinigrin, mustard from white mustard seeds has only a weakly pungent taste.The less sharp taste is because the mustard oil...
derived from tyrosine
Tyrosine
Tyrosine or 4-hydroxyphenylalanine, is one of the 22 amino acids that are used by cells to synthesize proteins. Its codons are UAC and UAU. It is a non-essential amino acid with a polar side group...
.
Enzymatic activation
The plants contain the enzyme myrosinaseMyrosinase
Myrosinase is a family of enzymes involved in plant defense against herbivores. Their structure has been elucidated and is available.-Myrosinase activity:...
, which, in the presence of water, cleaves off the glucose group from a glucosinolate. The remaining molecule then quickly converts to an isothiocyanate
Isothiocyanate
Isothiocyanate is the chemical group –N=C=S, formed by substituting sulfur for oxygen in the isocyanate group. Many natural isothiocyanates from plants are produced by enzymatic conversion of metabolites called glucosinolates. These natural isothiocyanates, such as allyl isothiocyanate, are also...
, a nitrile
Nitrile
A nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, one example being super glue .Inorganic compounds containing the -C≡N group are not called...
, or a thiocyanate
Thiocyanate
Thiocyanate is the anion [SCN]−. It is the conjugate base of thiocyanic acid. Common derivatives include the colourless salts potassium thiocyanate and sodium thiocyanate. Organic compounds containing the functional group SCN are also called thiocyanates...
; these are the active substances that serve as defense for the plant. Glucosinolates are also called mustard oil glycosides. The standard product of the reaction is the isothiocyanate (mustard oil); the other two products mainly occur in the presence of specialised plant proteins that alter the outcome of the reaction. To prevent damage to the plant itself, the myrosinase and glucosinolates are stored in separate compartments of the cell and come together only or mainly under conditions of physical injury.
Bitter, toxic – or healthy?
Because the use of glucosinolate-containing crops as primary food source for animals was shown to have negative effects, food crops that contain very low amounts of glucosinolates (e.g., canolaCanola
Canola refers to a cultivar of either Rapeseed or Field Mustard . Its seeds are used to produce edible oil suitable for consumption by humans and livestock. The oil is also suitable for use as biodiesel.Originally, Canola was bred naturally from rapeseed in Canada by Keith Downey and Baldur R...
) have been developed. The glucosinolate sinigrin
Sinigrin
Sinigrin is a glucosinolate that belongs to the family of glucosides found in some plants of the Brassicaceae family such as Brussels sprouts, broccoli, and the seeds of black mustard to name but a few...
, among others, was shown to be responsible for the bitterness of cooked cauliflower
Cauliflower
Cauliflower is one of several vegetables in the species Brassica oleracea, in the family Brassicaceae. It is an annual plant that reproduces by seed...
and Brussels sprouts.
On the other hand, plants producing large amounts of glucosinolates also are of interest because substances derived from them can serve as natural pesticides and are under investigation for mitigating cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
, with sulforaphane
Sulforaphane
Sulforaphane is an organosulfur compound that exhibits anticancer, antidiabetic, and antimicrobial properties in experimental models. It is obtained from cruciferous vegetables such as broccoli, Brussels sprouts or cabbages. The enzyme myrosinase transforms glucoraphanin, a glucosinolate, into...
from broccoli
Broccoli
Broccoli is a plant in the cabbage family, whose large flower head is used as a vegetable.-General:The word broccoli, from the Italian plural of , refers to "the flowering top of a cabbage"....
being the best known example. Consumers of higher levels of Brassica vegetables, particularly broccoli, Brussels sprouts and cabbage
Cabbage
Cabbage is a popular cultivar of the species Brassica oleracea Linne of the Family Brassicaceae and is a leafy green vegetable...
, may benefit from a lower risk of cancer at a variety of organ sites, although this information is neither scientifically conclusive nor approved by any national regulatory authority as of 2011. Brassica vegetables contain high concentrations of glucosinolates that the plant enzyme myrosinase or intestinal microflora can hydrolyze into isothiocyanates which, in preliminary research, are potent inducers of cytoprotective enzymes and inhibitors of carcinogenesis in vitro. These findings provide rationale for evaluating the protective effects of a broccoli sprout preparation in clinical trials of women at risk for breast cancer.
Effects on humans and other mammals
Glucosinolates are well known for their toxic effects (mainly as goitrogens) in both humans 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, such as the 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. In particular, the chemopreventive effects of the glucosinolates present in cruciferous vegetablesCruciferous vegetables
Vegetables of the family Brassicaceae are called cruciferous vegetables. The vegetables are widely cultivated, with many genera, species, and cultivars being raised for food production such as cauliflower, cabbage, cress, bok choy, broccoli and similar green leaf vegetables...
are related to their activity as Histone deacetylase inhibitor
Histone deacetylase inhibitor
Histone deacetylase inhibitors are a class of compounds that interfere with the function of histone deacetylase.HDIs have a long history of use in psychiatry and neurology as mood stabilzers and anti-epileptics...
s.
Relations to insect specialists
A characteristic, specialised insect fauna is found on glucosinolate-containing plants, including familiar butterflies such as Large WhiteLarge White
The Large White , also called Cabbage Butterfly, Cabbage White, or in India the Large Cabbage White, White cabbage butterfly is a butterfly in the family Pieridae.-Distribution:...
, Small White, and Orange Tip, but also certain aphids, moths, saw flies, flea beetles, etc. The biochemical basis of these specialisations are being unraveled. The whites and orange tips all possess the so-called nitrile specifier protein, which diverts glucosinolate hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
toward nitrile
Nitrile
A nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, one example being super glue .Inorganic compounds containing the -C≡N group are not called...
s rather than reactive isothiocyanate
Isothiocyanate
Isothiocyanate is the chemical group –N=C=S, formed by substituting sulfur for oxygen in the isocyanate group. Many natural isothiocyanates from plants are produced by enzymatic conversion of metabolites called glucosinolates. These natural isothiocyanates, such as allyl isothiocyanate, are also...
s. In contrast, the diamondback moth (Plutella xylostella) possesses a completely different protein, glucosinolate sulfatase, which desulfates glucosinolates, thereby making them unfit for degradation to toxic products by myrosinase.
Other kinds of insects (specialised sawflies and aphids) sequester glucosinolates. In specialised aphids, but not in sawflies, a distinct animal-myrosinase is found in muscle tissue, leading to degradation of sequestered glucosinolates upon aphid tissue destruction. This diverse panel of biochemical solutions to the same plant chemical plays a key role in current attempts to understand the evolution of plant-insect relationships.
See also
- IsothiocyanateIsothiocyanateIsothiocyanate is the chemical group –N=C=S, formed by substituting sulfur for oxygen in the isocyanate group. Many natural isothiocyanates from plants are produced by enzymatic conversion of metabolites called glucosinolates. These natural isothiocyanates, such as allyl isothiocyanate, are also...
- GluconasturtiinGluconasturtiinGluconasturtiin is a glucosinolate with the chemical name phenethylglucosinolate. It is one of the most widely distributed glucosinolates in the crucifers, mainly in the roots, and is probably one of the plant compounds responsible for the natural pest-inhibiting properties of growing crucifers,...
- GlucobrassicinGlucobrassicinGlucobrassicin is a type of glucosinolate that can be found in almost all cruciferous plants, such as cabbages , mustards, cress, and woad. As for other glucosinolates, degradation by the enzyme myrosinase is expected to produce an isothiocyanate, indol-3-ylmethylisothiocyanate...
- GoitrinGoitrinGoitrin is a sulfur-containing oxazolidine, a cyclic thiocarbamate, that reduces the production of thyroid hormones such as thyroxine. It is found in cruciferous vegetables such as cabbage, brussels sprouts and oil-seed rape, and is formed by the hydrolysis of a glucosinolate; 2-hydroxy-3-butenyl...
- SinigrinSinigrinSinigrin is a glucosinolate that belongs to the family of glucosides found in some plants of the Brassicaceae family such as Brussels sprouts, broccoli, and the seeds of black mustard to name but a few...
- SinalbinSinalbinSinalbin is a glucosinolate found in the seeds of white mustard, Sinapis alba, and in many wild plant species. In contrast to mustard from black mustard seeds which contain sinigrin, mustard from white mustard seeds has only a weakly pungent taste.The less sharp taste is because the mustard oil...
External links
- Glucosinolate metabolism pathways from MetaCyc