Biosynthesis of phenylpropanoids

Validation of the role of femloyl-CoA in the synthesis of the vanillin precursor will be detection of the appropriate intermediates and/or enzyme activities in placental extracts that could account for the production of the predicted levels of capsaicinoids. The presence of low levels of monolignol intermediates could be explained by lignin biosynthesis. An alternate route from phenylalanine to vanillin has been considered by some investigators Orlova et al. [68] demonstrated the role of the benzenoid pathway in petunia flowers for the biosynthesis of phenylpropanoid/benzenoid volatiles. 

The functions of phenylpropanoid derivatives are as diverse as their structural variations. Phenylpropanoids serve as phytoalexins, UV protectants, insect repellents, flower pigments, and signal molecules for plant-microbe interactions. They also function as polymeric constituents of support and surface structures such as lignins and suberins [1]. Therefore, biosynthesis of phenylpropanoids has received much interest in relation to these functions. In addition, the biosynthesis of these compounds has been intensively studied because they are often chiral, and naturally occurring samples of these compounds are usually optically active. Elucidation of these enantioselective mechanisms may contribute to the development of novel biomimetic systems for enantioselective organic synthesis. 

Figure 1. Phenylalanine ammonia-lyase (PAL) involvement in the biosynthesis of phenylpropanoid-derived secondary metabolites in plants and Ba-sidiomycetes.

Petersen, M., Strack, D., and Matern, U., Biosynthesis of phenylpropanoids and related compounds, in Biochemistry of Plant Secondary Metabolism, Wink, M., Ed., Sheffield Academic Press, Sheffield, 1999, 151. 

Chappie, . C. S. and . E. Ellis. 1991. Syringa vulgaris L. (common lilac) in vitro culture and the occurrence and biosynthesis of phenylpropanoid glycosides. In Bajaj, Y. P. S. (ed.). Biotechnology in Agriculture and Forestry 15. Medicinal and Aromatic Plants III. Springer-Verlag. New York. p. 478-497. 

Ferrer J-L, Austin MB, Stewart C, Noel JP. 2008. Structure and function of enzymes involved in the biosynthesis of phenylpropanoids. Plant Physiol Biochem 46 356-370. 

Biosynthesis of Phenylpropanoids and Related Compounds 203 4.3.1.2 Alkylated umbelliferone... 

Arahidopsis has become the model system of choice in which to study many aspects of plant growth, development, and metabolism, including the biosynthesis of phenylpropanoid natural products. This is, in part, because Arabidopsis accumulates two classes of phenylpropanoid end products that are good targets for mutant screens. For example, many screens have identified mutants defective in fiavonoid biosynthesis. Defects in this pathway in Arahidopsis lead to transparent testa (tt) and transparent testa glabrous (ttg) phenot3Tjes that result from decreases in the condensed tannins found in the seed coat. These mutants have already been exhaustively reviewed, and hence will not be covered here. 

L-phenylalanine, L-a-aminooxy-g-phenylpropionic acid (AOPP, in Fig. 9) should have an increased inhibitory ability. This was confirmed beyond our expectations, as L-AOPP inhibited buckwheat PAL with a Ki of 1.4 nM (Table 2) and also inhibited the biosynthesis of phenylpropanoid compounds in vivo without deleterious effects on normal plant development. Selective accumulation of phenylalanine in... 

Petersen M, Strack D, Matem U (1999) Biosynthesis of phenylpropanoids and related compounds. In Wink M (ed) Biochemistry of plant secondary metabolism, vol 2. Sheffield Academic Press/CRC Press, Sheffield/Boca Raton, pp 151-222... 

---