This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: p-hydroxybenzoate biosynthesis IV
|Superclasses:||Biosynthesis → Aromatic Compounds Biosynthesis → 4-Hydroxybenzoate Biosynthesis|
Expected Taxonomic Range: Viridiplantae
4-hydroxybenzoate (p-hydroxybenzoate) is widespread in plants. It is one of the major cell wall-bound phenolic acids that play a major role in plant defense against pathogens. It has also been identified as an important dietary anti-oxidant. In addition, 4-hydroxybenzoate is a key intermediate in the biosynthesis of ubiquinone-9 and several plant secondary metabolites, such as shikonin.
There are at least two biosynthetic routes leading to 4-hydroxybenzoate that have been proposed in plants: 1) the beta-oxidation route that converts 4-coumarate to 4- hydroxybenzoate via 4-coumaroyl-CoA; and 2) the non-beta oxidative pathway that converts 4-coumarate to 4- hydroxybenzoate via 4- hydroxybenzaldehyde. In plants, 4- hydorxybenzoate has an origin from phenylalanine where 4-coumarate is an intermediate and cleavage of two carbons from the 4-coumarate side-chain is required [Sircar08, Yazaki91, Loscher94]. In the beta-oxidation pathway, the side-chain shortening is analogous to fatty acid β-oxidation II (peroxisome) via CoA esters. In the non-oxidative pathway, the side-chain shortening is achieved through a lyase reaction that does not require CoA as a cofactor.
About This Pathway
The existence of the non-beta oxidation pathway has been reported in a number of plant species including, but not limited to, Lithospermum erythrorhizon and Daucus carota. In carrot, the accumulation of p-hydroxybenzoate in hairy root culture was dramatically increased by methyl jasmonate (MeJA) treatment. The enzymatic activities of the first and last enzymes of the biosynthetic pathway, phenylalanine ammonia-lyase (PAL) and 4-hydroxybenzaldehyde dehydrogenase (HBD) were coordinately increased by MeJA treatment [Sircar08].
Loscher94: Loscher R, Heide L (1994). "Biosynthesis of p-Hydroxybenzoate from p-Coumarate and p-Coumaroyl-Coenzyme A in Cell-Free Extracts of Lithospermum erythrorhizon Cell Cultures." Plant Physiol 106(1);271-279. PMID: 12232327
Sircar08: Sircar D, Mitra A (2008). "Evidence for p-hydroxybenzoate formation involving enzymatic phenylpropanoid side-chain cleavage in hairy roots of Daucus carota." J Plant Physiol 165(4);407-14. PMID: 17658659
Yazaki91: Yazaki, Kazufumi, Heide, Lutz, Tabata, Mamoru (1991). "Formation of p-hydroxybenzoic acid from p-coumaric acid by cell free extract of Lithospermum erythrorhizon cell cultures." Phytochemistry, 30(7):2233-2236.
Bossert89: Bossert ID, Whited G, Gibson DT, Young LY (1989). "Anaerobic oxidation of p-cresol mediated by a partially purified methylhydroxylase from a denitrifying bacterium." J Bacteriol 1989;171(6);2956-62. PMID: 2722739
Gunsalus53: Gunsalus CF, Stanier RY, Gunsalus IC (1953). "The enzymatic conversion of mandelic acid to benzoic acid. III. Fractionation and properties of the soluble enzymes." J Bacteriol 66(5);548-53. PMID: 13108854
Podstolski02: Podstolski A, Havkin-Frenkel D, Malinowski J, Blount JW, Kourteva G, Dixon RA (2002). "Unusual 4-hydroxybenzaldehyde synthase activity from tissue cultures of the vanilla orchid Vanilla planifolia." Phytochemistry 61(6);611-20. PMID: 12423881
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