Alkaloids biosynthetic pathway

Based on the amino acid of origin in their biosynthetic pathway, alkaloids can be divided into the following five major classes [2] ... 

Fig. 18 Reconstructed isoquinoline alkaloid biosynthetic pathway in microbes (E. coli and S. cerevisiae) [120]. Accession numbers of the genes can be taken from Gene Bank. C3,4-DHPA-A 3,4-dihydroxyphenylacetaldehyde NCS norcoclaurine synthase 60MT 6-0-methyltransferase CNMT coclaurine-/V-mcthyltransferase 4 OMT 4 -0-methyltransferase BBE berberine bridge enzyme NMT /V-methyltransferase)...

Regulation of the Terpenoid Indole Alkaloid Biosynthetic Pathway 111... 

Alkaloid biosynthetic pathways are under strict regulation in plants. Until now, our limited knowledge of the fundamental mechanisms involved in the control of alkaloid metabolism has severely restricted our ability to harness the vast biotechnological potential of these important secondary pathways. For example, the use of plant cell cultures for the commercial production of pharmaceutical alkaloids has not become a reality despite decades of empirical research. The application of traditional and modem biochemical, molecular, and cellular techniques has revealed important clues about the reasons why C. rosens cultures accumulate tabersonine and catharanthine, but not vindoline or vinblastine, and why opium poppy cultures produce sanguinarine, but not codeine or morphine. The inability of dedifferentiated cells to accumulate certain metabolites was interpreted as evidence that the operation of many alkaloid pathways is tightly coupled to the development of specific tissues. Recent studies have shown that alkaloid pathways are regulated at multiple levels,... 

DE LUCA, V., BALSEVICH, J., TYLER, R.T., KURZ, W.G.W, Characterization of a novel V-methyltransferase (NMT) from Catharanthus roseus plants. Detection of NMT and other enzymes of the indole alkaloid biosynthetic pathway in different cell suspension culture systems. Plant Cell Rep., 1987,6,458-461. 

MENKE, F.L., PARCHMANN, S., MUELLER, M.J., KUNE, J.W., MEMELINK, J., Involvement of the octadecanoid pathway and protein phosphoiylation in fungal elicitor-induced expression of terpenoid indole alkaloid biosynthetic genes in Catharanthus roseus. Plant Physiol., 1999,119, 1289-1296. 

Alkaloids thus represent one of the largest groups of natural products, with over 10,000 known compounds at present, and they display an enormous variety of structures, which is due to the fact that several different precursors find their way into alkaloid skeletons, such as ornithine, lysine, phenylalanine, tyrosine, and tryptophan (38-40). In addition, part of the alkaloid molecule can be derived from other pathways, such as the terpenoid pathway, or from carbohydrates (38-40). Whereas the structure elucidation of alkaloids and the exploration of alkaloid biosynthetic pathways have always commanded much attention, there are relatively few experimental data on the ecological function of alkaloids. This is the more surprising since alkaloids are known for their toxic and pharmacological properties and many are potent pharmaceuticals. 

F. (1). Tropane alkaloids biosynthetic pathway. The known enzymes are indicated. ODC (ornithine decarboxylase), ADC (arginine decarboxylase), PMT (putrescine methyl transferase), MPO (methyl putrescine oxidase), TRI, TRII (tropinone reductase I, II), H6H (hyoscyamine 6p hydroxylase). 

In this section, an overview of the known enz5mies participating in the different steps of the tropane alkaloid biosynthetic pathway, as well as the genetic manipulation of these enzymes and the efforts for... 

Nevertheless, genetic engineering of a key enzyme in a chosen pathway does not always result in the enhancement of the end product thus, overexpression of pmt gene carried out in A. belladonna resulted in a 5-fold increased in pmt transcript level but an unchanged tropane alkaloid profile (hyoscyamine and scopolamine), as well as the tropane alkaloids biosynthetic precursors tropine, pseudotropine and tropinone which were not affected [134-135], Similarly, the overexpression of tobacco pmt gene in Dubosia hybrid hairy root cultures produced amounts of tropane alkaloid similar to control roots [131, 136]. All these results seem to indicate the presence of different points of control in the tropane alkaloid metabolic pathway. 

A-methylputrescine oxidase catalyzes the formation of N-methylpyrrolinium cation, an important intermediate of tropane alkaloids biosynthetic pathway as well as of nicotine. Fig. (1). The... 

The engineering of tropane alkaloids biosynthetic pathway by overexpression genes participating in that pathway constitutes and important tool for scopolamine and hyoscyamine enhancement. Thus, no much attention has been given to TRI and TRII genes and only two reports describe the manipulation of these genes. 

The early steps in the ergot alkaloid biosynthetic pathway are outlined in Fig. 1. The first determinant and rate-limiting step is the prenylation of tryptophan to 4-(y,y-dimethylallyl)tryptophan (DMAT), catalyzed by dimethy-lallyl-diphosphate L-tryptophan dimethylallyltransferase (DMAT synthase EC 2.5.1.34) (Heinstein et al., 1971 Gebler and Poulter, 1992). The prenyl group for the DMAT synthase reaction is provided in the form of dimethylallyl diphosphate (DMAPP), which is derived from mevalonic acid. After the formation of DMAT, the free amino group of this intermediate is N-methylated with a methyl group donated by S-adenosylmethionine (AdoMet). The N-methylated DMAT is then converted into chanoclavine I by closure of the... 

We do not intend to deal here with all of the various approaches to increase alkaloid accumulation in C. roseus plant cell cultures. Rather, we want to evaluate these studies in terms of regulation and signals that affect the alkaloid biosjmthesis. Such information may hold clues for the use of metabolic engineering of the alkaloid biosynthetic pathway. 

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