Evidence for enzyme complexes in the phenylpropanoid and flavonoid pathways

Abstract

A growing body of evidence indicates that phenylpropanoid and flavonoid metabolism is catalyzed, not by free‐floating ‘soluble’ enzymes, but via one or more membrane‐associated multienzyme complexes. This type of macromolecular organization has important implications for the overall efficiency, specificity, and regulation of these pathways. Classical biochemical studies of phenylpropanoid and flavonoid metabolism have laid a solid foundation for this model, providing evidence of the channeling of intermediates between enzyme active sites and co‐localization of enzymes in cell membranes. This work is now being extended using transgenic plants to determine how the partitioning of metabolites within these pathways is controlled, as well as applying sensitive methods to define specific interactions among the individual enzymes. Information from these studies promises to provide new insights into the structuring of biosynthetic pathways within cells, which should lead to more effective means for engineering the production of plant metabolites with nutritional and agronomic importance.

Functional Conservation of Plant Secondary Metabolic Enzymes Revealed by Complementation of Arabidopsis Flavonoid Mutants with Maize Genes

“…The substrate specificity of the Gerbera DFR was altered recently by a single amino acid change (Johnson et al, 2001), suggesting that very related DFR enzymes can have a strong preference of one substrate over another. An alternative explanation for our findings is that the TT7-encoded F3ЈH enzyme plays a key role in substrate channeling in the complex formed by the Arabidopsis flavonoid biosynthetic enzymes (Burbulis and Winkel-Shirley, 1999;Winkel-Shirley, 1999). If so, it appears that the maize A1 protein can participate in the metabolic channel in a manner similar to the DFR encoded by the endogenous Arabidopsis TT3 gene.…”

“…This unexpected decrease in cyanidin accumulation might be due to a partial inhibitory effect of the maize CHI1 enzyme on the endogenous CHI; for example, by competing for interaction with CHS (Burbulis and Winkel- Shirley, 1999). The observed formation of an increased amount of K relative to Q in plants expressing the maize CHI1 enzyme (Fig.…”

“…The contribution of branched pathways to the formation of different flavonoid compounds from the various possible precursors is poorly established. Evidence that Arabidopsis flavonoid biosynthetic enzymes physically interact (Burbulis and Winkel-Shirley, 1999) suggests that the formation of different multiprotein complexes may contribute to the biosynthesis of each group of flavonoids (Winkel-Shirley, 1999).…”

Shoot Epicatechin and Epigallocatechin Contents Respond to Water Stress in Tea [Camellia sinensis(L.) O. Kuntze]

“…Flavonoid biosynthesis is dependent on structural and regulatory genes; structural genes encode enzymes catalyzing the biosynthesis, while regulatory genes control the expression of the genes. 8,[10][11][12][13][14] This implies that the availability and quantity of certain flavonoids in plant tissues is an indication of plant response to either internal or external stimuli.As observed in some plants, the production of certain secondary metabolites serves as a signal generated by an external factor, and manifested at the molecular level, prior to morphological symptoms. For instance, increased biosynthesis of the phytoalexin medicarpin in alfalfa has been observed in response to fungal attack.…”

Subcellular Localization Studies of Three Phenylalanine Ammonia-Lyases and Cinnamate 4-Hydroxylase from <i>Scutellaria Baicalensis</i> Using GFP Fusion Proteins

“…C4H anchors the enzyme complex, formed by the general phenylpropanoid enzymes, to the ER membrane (Winkel-Shirley, 1999). The ER localization of C4H has previously been shown in the hybrid poplar (Ro et al, 2001).…”