Phenylpropanoid Metabolism: The Lignan Branch

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Lignans and neolignans are an ever-increasingly important class of compounds ubiquitous throughout the plant kingdom, whose rather remarkable plant defense, phytoalexin, cell-division promoting and pharmaceutical properties are only now beginning to be fully recognized. Although they are most often found enantiomerically pure, the mechanisms by which their achiral precursors undergo stereoselective coupling, and their subsequent postcoupling enantiospecific transformations, have eluded definition for several decades. This proposal addresses the essential unknown biochemistry of major class of phenylpropanoid metabolites, the lack of knowledge of which has placed an enormous constraint on our ability to study this area of metabolism at the gene level. The prognosis is, however, excellent: recent studies in this laboratory resulted in the discovery of a highly unusual, novel coupling enzyme which directly and sterioselective couples achiral precursors: it is not a typical H2O2-dependent peroxidase. Thus, one can systematically determine its mechanism of action and to define the scope of the transformations that can be engendered by this enzyme. In a similar vein, the enantiospecificity of post- coupling transformations can be systematically examined. Consequently, this study will bring order to this apparently chaotic branch of phenylpropanoid metabolism in terms of elucidating biochemical pathways involved. Following purification of the enzymes of interest to apparent homogeneity, the application of immunocytochemical methodologies will permit us to determine the subcellular location and tissue specificity of lignan formation, and whether metabolite channeling into lignan and lignin pathways occurs. %%% Plants are well known for their ability to produce novel chemical compounds which can be utilized in both medical and industrial use by humans. Often chemical synthesis of these compounds is impractical due the detailed chemistry of some of the compounds. However, by first purifying the enzymes in the plant essential steps in the biochemical pathway are understood and often an essential step in the chemical synthesis can be overcome. Furthermore, this leads to isolation of the genes responsible for the enzyme production and the capability to express the compound in other plants. The class of compounds called lignans are novel biochemicals which can be use an novel biomaterials. This research will study the enzymes and the reactions necessary for their synthesis.