Apigenin on:
[Wikipedia]
[Google]
[Amazon]
Apigenin (4′,5,7-trihydroxyflavone), found in many plants, is a natural product belonging to the flavone class that is the aglycone of several naturally occurring glycosides. It is a yellow crystalline solid that has been used to dye wool.
Apigenin is biosynthetically derived from the general phenylpropanoid pathway and the flavone synthesis pathway. The phenylpropanoid pathway starts from the aromatic amino acids L-phenylalanine or L-tyrosine, both products of the Shikimate pathway. When starting from L-phenylalanine, first the amino acid is non-oxidatively deaminated by phenylalanine ammonia lyase (PAL) to make cinnamate, followed by oxidation at the ''para'' position by cinnamate 4-hydroxylase (C4H) to produce ''p''-coumarate. As L-tyrosine is already oxidized at the ''para'' position, it skips this oxidation and is simply deaminated by
Sources in nature
Apigenin is found in many fruits and vegetables, but parsley, celery, celeriac, and chamomile tea are the most common sources. Apigenin is particularly abundant in the flowers of chamomile plants, constituting 68% of total flavonoids. Dried parsley can contain about 45 mg apigenin/gram of the herb, and dried chamomile flower about 3-5 mg/gram. The apigenin content of fresh parsley is reportedly 215.5 mg/100 grams, which is much higher than the next highest food source, green celery hearts providing 19.1 mg/100 grams.Biosynthesis
Apigenin is biosynthetically derived from the general phenylpropanoid pathway and the flavone synthesis pathway. The phenylpropanoid pathway starts from the aromatic amino acids L-phenylalanine or L-tyrosine, both products of the Shikimate pathway. When starting from L-phenylalanine, first the amino acid is non-oxidatively deaminated by phenylalanine ammonia lyase (PAL) to make cinnamate, followed by oxidation at the ''para'' position by cinnamate 4-hydroxylase (C4H) to produce ''p''-coumarate. As L-tyrosine is already oxidized at the ''para'' position, it skips this oxidation and is simply deaminated by tyrosine ammonia lyase
Tyrosine ammonia lyase (EC 4.3.1.23, L-tyrosine ammonia-lyase, TAL or Tyrase) is an enzyme in the natural phenols biosynthesis pathway. It transforms L-tyrosine into ''p''-coumaric acid.
: \xrightarrow + Ammonia + H+
L-tyrosine = ''tr ...
(TAL) to arrive at ''p''-coumarate. To complete the general phenylpropanoid pathway, 4-coumarate CoA ligase (4CL) substitutes coenzyme A (CoA) at the carboxy group of ''p''-coumarate. Entering the flavone synthesis pathway, the type III polyketide synthase enzyme chalcone synthase (CHS) uses consecutive condensations of three equivalents of malonyl CoA followed by aromatization to convert ''p''-coumaroyl-CoA to chalcone. Chalcone isomerase (CHI) then isomerizes the product to close the pyrone ring to make naringenin. Finally, a flavanone synthase (FNS) enzyme oxidizes naringenin to apigenin. Two types of FNS have previously been described; FNS I, a soluble enzyme that uses 2-oxogluturate, Fe2+, and ascorbate as cofactors and FNS II, a membrane bound, NADPH dependent cytochrome p450 monooxygenase.
Glycosides
The naturally occurring glycosides formed by the combination of apigenin with sugars include: * Apiin (apigenin 7-''O''-apioglucoside), isolated from parsley and celery * Apigetrin (apigenin 7-glucoside), found indandelion coffee
Dandelion 'coffee' (also dandelion tea) is a herbal tea, tisane made from the root of the Taraxacum, dandelion plant. The roasted dandelion root pieces and the beverage have some resemblance to coffee in appearance and taste, and it is thus commo ...
* Vitexin (apigenin 8-''C''-glucoside)
* Isovitexin (apigenin 6-''C''-glucoside)
* Rhoifolin (apigenin 7-''O''- neohesperidoside)
* Schaftoside (apigenin 6-''C''-glucoside 8-''C''-arabinoside)
See also
* AmentoflavoneReferences
{{Progestogenics Aromatase inhibitors Delta-opioid receptor antagonists Flavones GABAA receptor positive allosteric modulators Resorcinols Kappa-opioid receptor antagonists Mu-opioid receptor antagonists NMDA receptor antagonists Phytoestrogens Progestogens Vinylogous carboxylic acids