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.
|Superclasses:||Biosynthesis → Secondary Metabolites Biosynthesis → Phenylpropanoid Derivatives Biosynthesis → Hydrolyzable Tannins Biosynthesis|
Expected Taxonomic Range: Magnoliophyta
Hydrolyzable tannins (HT), divided in the two subclasses gallotannins (see gallotannin biosynthesis) and ellagitannins (see cornusiin E biosynthesis) are derivatives of 1,2,3,4,6-pentagalloylglucose [Niemetz00]. The category 'hydrolyzable tannins' is based on the classical definition of Freudenberg [Freudenberg20] who distinguished condensed tannins (also referred to as proanthocyanins; flavonoid origin) and hydrolyzable tannins (esters of gallic acid with typically β-D-glucose). That class of compounds belongs to the more general 'plant polyphenols' (synonym vegetable tannins) which have been intensively studied in the last few decades (reviewed in [Haslam89, Haslam94, Haslam98]).
The name 'tannin' derived from the pronounced property of these compounds to precipitate proteins which has been used over the centuries for the tannery procedure to produce endurable leather from raw hides. Beside that, hydrolyzable tannins have many antimicrobial, antioxidant and antitumor properties used in human health care [Haslam96] and apply the varying amount of astringency as food components/phytonutrients [Beecher03]. Hydrolyzable tannins are widely distributed among plants but differ with regard to gallotannins (more restricted occurence) and ellagitannins (broad occurence) [Haddock82a].
Hydrolyzable tannins and corresponding enzymes have been localized to the walls of leaf mesophyll cells, vitiating the former hypothesis of 'tannin vacuoles' as major sites for HT formation and deposition. The biogenesis of hydrolyzable tannins also followed a discernible seasonal pattern with galloylglucoses being formed in spring, a peak of ellagitannin biosynthesis observed in summer and tannin degradation taking place in fall [Grundhofer01].
The mono- to penta-substituted esters being generated on the biogenetic way towards pentagalloylglucose are also referred to as 'simple' galloylglucoses in contrast to the 'complex' galloylglucoses produced as the result of further galloylation of pentagalloylglucose [Niemetz05]. However, that categorization does not indicate the tanning potential of the associated compounds.
About This Pathway
The biosynthesis towards pentagalloylglucose displays a high specificity with a defined metabolic sequence. The first step is the formation of 1-O-galloyl-β-D-glucose from gallic acid catalyzed by the UDPG-dependent gallate-1-β-glucosyltransferase [Gross83a]. This compound does not only function as the common acyl acceptor throughout the pentagalloylglucose biosynthetic pathway but exerts in addition a dual role as acyl donor indicating the characteristic of an energy-rich 'activated' compound [Gross83].
The further galloylation follows the metabolic sequence 1,6-digalloylglucose mediated by β-glucogallin O-galloyltransferase [Schmidt87], 1,2,6-trigalloylglucose formed by the enzyme β-glucogallin dikisgalloylglucose O-galloyltransferase [Gross91], 1,2,3,6-tetragalloylglucose being catalyzed by β-glucogallin trikisgalloylglucose O-galloyltransferase [Hagenah93] and finally 1,2,3,4,6-pentagalloylglucose that is formed by β-glucogallin tetrakisgalloylglucose O-galloyltransferase [Cammann89].
The formation of 1,2,6-trigalloylglucose can also be catalyzed by an enzyme, i.e. l,6-di-O-galloylglucose: 1,6-di-O-galloylglucose 2-O-galloyltransferase that has been isolated and characterized in Rhus typhina [Denzel91]. This reaction gives rise to a alternative route, using only the substrate 1,6-digalloylglucose instead of the usual β-glucogallin, therefore defined as 'disproportionation'.
Superpathways: superpathway of hydrolyzable tannin biosynthesis
Cammann89: Cammann J, Denzel K, Schilling G, Gross GG (1989). "Biosynthesis of gallotannins: β-glucogallin-dependent formation of 1,2,3,4,6-pentagalloylglucose by enzymatic galloylation of 1,2,3,6-tetragalloylglucose." Arch Biochem Biophys 273(1);58-63. PMID: 2757399
Denzel91: Denzel K, Gross GG (1991). "Biosynthesis of gallotannins. Enzymatic 'disproportionation' of 1,6-digalloylglucose to 1,2,6-trigalloylglucose and 6-galloylglucose by an acyltransferase from leaves of Rhus typhina L." Planta, 184, 185-289.
Haddock82a: Haddock EA, Gupta RK, Al-Shafi SM, Layden K, Haslam E, Magnolato D (1982). "The metabolism of gallic acid and hexahydroxydiphenic acid in plants: biogenetic and molecular taxonomic considerations." Phytochemistry, 21(5), 1049-1062.
Niemetz00: Niemetz R, Niehaus JU, Gross GG (2000). "Biosynthesis and biodegradation of complex gallotannins." In: Gross, GG., Hemingway, RW. and Yoshida, T. (eds.) Plant Polyphenols 2: Chemistry and Biology, 63-83. Kluwer Academic/Plenum Publishing Corporation, New York, Boston, Dordrecht, London, Moscow.
Schmidt87: Schmidt SW, Denzel K, Schilling G, Gross GG (1987). "Enzymatic synthesis of 1,6-digalloylglucose from β-glucogallin by β-glucogallin: β-glucogallin 6-O-galloyltransferase from Oak leaves." Z. Naturforsch., 42c, 87-92.
Mittasch14: Mittasch J, Bottcher C, Frolova N, Bonn M, Milkowski C (2014). "Identification of UGT84A13 as a candidate enzyme for the first committed step of gallotannin biosynthesis in pedunculate oak (Quercus robur)." Phytochemistry. PMID: 24412325
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