Terpenoid indole alkaloids tryptophan, pathway

Figure 8,2 Terpenoid indole alkaloid biosynthetic pathway. AS anthranilate synthase TDC tryptophan decarboxylase ...

Fig. (3). Compartmentalization of the biosynthetic pathway of terpenoid indole alkaloids in plant cells. G10H geraniol 16-hydroxylase SLS secologanin synthase TDC tryptophan decarboxylase STR strictosidine synthase SGD strictosidine P-D-glucosidade T16H tabersonine 16-hydroxylase OMT S-adenosyl - L-methionine 16-hydroxytabereonine - 16-O-methyltransferase NMT S-adenosyl - /.-methionine 16-methoxy - 2,3-dihydro-3-hydroxytabersonine - A -methyltransferase D4H desacetoxy vindoline 4-hydroxylase DAT acetylcoenzyme A 4-O-deacetylvindoline 4-O-aeetyltransferase PRX peroxidase.

In the present review we divide the pathway leading to the Catharanthus alkaloids into five parts (Fig. 2). The first two concern the biosynthesis of tryptophan and geraniol diphosphate they are similar to (or even part of) primary metabolism and occur in all plant species. Whether these pathways in C. roseus are differently regulated, or whether even an additional pathway exists parallel to the normal primary metabolism, is a question not yet answered. The third and the fourth part coneern the steps from tryptophan to tryptamine and from geraniol to secologanin, respectively. Both pathways occur also in other plants, including plants that do not produce terpenoid indole alkaloids. The fifth part is the condensation of secologanin and tryptamine to strictosidine and the subsequent conversion into a plethora... 

The indole moiety of the terpenoid indole alkaloids originates from tryptophan, an aromatic amino acid, which is derived from chorismate via anthranilate. Chorismate is a major branching point in plant primary and secondary metabolism. Here the shikimate pathway (Fig. 6) branches into different pathways (Fig. 7), among others leading to the aromatic amino acids tyrosine, phenylalanine, and tryptophan. 

Indole alkaloids are derived from tr)y)tophan, which is formed in the shiki-mate pathway. In the case of the terpenoid indoles, tryptophan is usually first converted to tiyptamine by the enzyme tryptophan decarboxylase (TDC) (Fig. 2.9). This enz)une occurs in the cytosol and has been detected in all parts of the developing seedling and in cell cultures of C. roseus (De Luca, 1993). If appears to be a pyridoxoquinoprotein, as two molecules of pyridoxal phosphafe and two molecules of covalently bound pyrroloquinoline quinone were found per enz)une molecule (Pennings et al, 1989). A tdc cDNA clone has been isolafed by immunoscreening of a C. roseus cDNA expression library (De... 

L-Tryptophan is an indole ring containing aromatic amino acid derived via the shikimate pathway. The tryptophan-derived alkaloids are found in eight families, of which, Apocynaceae, Loganiaceae, Rubiaceae, and Nyssaceae are the best sources. The alkaloids under discussion are the Catharanthus alkaloids, namely, ajmalicine, tabersonine, catharanthine, vindoline, vinblastine, vincristine and vincamine as well as terpenoid alkaloids derived from other families, namely, yohimbine, reserpine, strychnine, brucine, and ellipticine. The above-mentioned alkaloids are pharmacologically very important and hence extremely valuable. This chapter describes various aspects of the tryptophan-derived alkaloids like occurrence, biological activity, phytochemistry, and commercial and biotechnological aspects. 

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