Phytyl-pyrophosphate

Animals caimot synthesize the naphthoquinone ring of vitamin K, but necessary quantities are obtained by ingestion and from manufacture by intestinal flora. In plants and bacteria, the desired naphthoquinone ring is synthesized from 2-oxoglutaric acid (12) and shikimic acid (13) (71,72). Chorismic acid (14) reacts with a putative succinic semialdehyde TPP anion to form o-succinyl benzoic acid (73,74). In a second step, ortho-succmY benzoic acid is converted to the key intermediate, l,4-dihydroxy-2-naphthoic acid. Prenylation with phytyl pyrophosphate is followed by decarboxylation and methylation to complete the biosynthesis (75). 

FIGURE 1.3 General biosynthetic pathway of tocopherols in chloroplasts and proplasts of plant cells. Biosynthesis of tocotrienols is similar except for reduction of geranylgeranyl pyrophosphate to phytyl pyrophosphate, which is omitted. SAM =. S -adenosylmethtontnc. [Data modified from Hess (1993).]... 

Biosynthesis T. are formed in higher plants, algae, and bacteria from phytyl pyrophosphate and homo-gentisic acid, animal organisms are not able to synthesize T. 

Liljenberg (1977a) has reviewed the phytylation step in chlorophyll biosynthesis and has presented evidence for the presence of phytyl pyrophosphate and acyl esters of phytol in irradiated barley seedlings (Liljenberg, 1977b). 

Mevalonate kinase [E.C.2.7.1.36 (5) -> (6)] preparations from several plants are inhibited by geranyl, geranylgeranyl, farnesyl, and phytyl pyrophosphates, the most potent inhibitors being the latter two compounds.This enzyme may, therefore, be a control point of isoprenoid biosynthesis in plants. A cell-free system for conversion of mevalonic acid (5) into mevalonic acid S-pyro-phosphate (7) has been prepared from the sapogenin-producing plant Agave americana. ... 

Transcripts that encode all of the enzymes involved in the biosynthesis of vitamin E are elucidated in Table 18.2. The identified enzymes used to reconstruct the pathway of vitamin E bios5mthesis are presented in Fig. 18.3. The vitamin E biosynthetic pathway in D. tertiolecta is similar to that of the plant AraUdopsis thaliana, and the cyanobacterium Synecho-cystis sp. D. tertiolecta utilizes the metabolism of the aromatic amino acid tyrosine for the s5mthesis of the polar head group, whereas the unsaturated tail is derived from phytyl-pyrophosphate (PPP), which is a metabolite of terpenoid backbone biosynthesis (DellaPenna and Pogson, 2006). The committed step in the synthesis of the head group is catalyzed by the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27), which converts... 

On the basis of the configuration of the four chiral centers, a biosynthetic pathway can be proposed with phytol as precursor. In this mechanism, two phytyl chains would condense, probably as pyrophosphate derivatives, to produce the prelycopadiene pyrophosphate (46), which would be converted to lycopadiene (45) by addition of a hydride ion to a rearranged cyclopropylcation. An intermediate analogous to (46) is known to occur in the synthesis of phytoene, the precursor of the carotenoids in this latter case two geranylgeranyl pyrophosphates are condensed (45). In another possible pathway, lycopadiene (45) would merely result from reduction of phytoene. 

GGPP is a key branch point metabolite of polyisoprenoid metabolism. Apart from the cyclic diterpenes, it is the precursor of the tetraterpenes (carotenes, xanthophylls), and acyclic diterpenes (phytol). Cyclic diterpenes compete with compounds of established importance for either GGPP or its precursors (e.g., famesyl pyrophosphate). The spotty nature of resin diterpene distribution may in part be explained by the obvious demand for carotenoids and phytyls and the relatively unestablished requirement for these nongibberellin diterpenes. 

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