Enzymes isoquinoline biosynthesis

Biosynthetic research relating to the isoquinoline family was extremely successful, with such important members as morphine [3, 14], codeine [3, 15] or berberine [3, 14,16-18]. Extensive efforts have provided details pertaining to multiple sets of enzymes participating in the biosynthesis of the alkaloids above, in many cases with the help of plant cell suspension culture techniques. Since 1988, when the breakthrough in cloning of cDNA from alkaloid biosynthesis occurred [19, 20], a significant number of enzymes known from the indoles and isoquinolines biosynthesis have been isolated, their biochemical properties described and the majority of their corresponding cDNAs cloned and functionally over-expressed in non-plant hosts such as Escherichia coli, yeast or insect cells. 

Isoquinoline biosynthesis begins with the substrates dopamine and p-hydroxyphenylacetaldehyde (Fig. lb). Dopamine is made from tyrosine by hydroxylation and decarboxylation. Enzymes that catalyze the hydroxylation and decarboxylation steps in either order exist in the plant, and the predominant pathway... 

The localization of isoquinoline biosynthesis has been investigated at the cellular level in intact poppy plants by using in situ RNA hybridization and immunoflouresence microscopy. The localization of 4 -OMT (reticuline biosynthesis), berberine bridge enzyme (saguinarine biosynthesis), salutaridinol acetyltransferase (morphine biosynthesis), and codeinone reductase (morphine biosynthesis) has been probed. 4 -OMT and salutaridinol acetyltransferase are localized to parenchyma cells, whereas codeinone reductase is localized to laticifer cells in... 

Fig. 10.8 Selected cDNAs isolated in recent years that encode enzymes involved in the biosynthesis of various classes of isoquinoline alkaloids. 6-OMT, norcoclaurine 6-0-methyltransferase 23 CYP80A1, berbamunine synthase 19 CYP80B1, (S)-A-methylcoclaurine 3 -hydroxylase 20 CPR, cytochrome P-450 reductase 29 4 -OMT, (5)-3 -hydroxy-A-methylcoclaurine 4 -0-methyltransferase 30 BBE, berberine bridge enzyme 12 SalAT, salutaridinol 7-O-acetyltransferase 28 COR, codeinone reductase.25...

In summary, the de novo isolation of the cDNAs encoding enzymes of alkaloid biosynthesis is still achieved by using a variety of classical techniques, such as protein purification followed by partial amino acid sequence determination, and by newer techniques such as proteomics coupled to functional heterologous expression. The current status of cloned cDNAs specifically related to isoquinoline alkaloid biosynthesis is schematically presented in Figure 10.8. New additions to this list will certainly be made in the future as a result of a combination of approaches both new and old. 

The benzylisoquinolines are formed from two molecules of fhe aromafic amino acid, tyrosine. In the past ten years, this pathway has been probed at the enzyme and gene level. The recent linking of the phloem-specific expression of tyrosine/Dopa decarboxylase (TYDC) genes with the bios)mthesis of the isoquinoline alkaloids in the opium poppy, Papaver somniferum (Facchini and De Luca, 1994, 1995, 2008 Liscombe and Facchini, 2008), and the association with alkaloid accumulation as part of the plant defence mechanism (Wink, 1993 Facchini et al, 1996) are of particular interest in furthering our knowledge of the location of alkaloid biosynthesis. 

Tyrosine decarboxylase, which is a key enzyme in the biosynthesis of isoquinoline alkaloids in plants, also occurs in all kingdoms of life (Fig. 7.16b, Table 7.3). The enz)mie catalyses the decarboxylation of tyrosine... 

The isoquinoline alkaloids include the analgesics morphine and codeine as well as the antibiotic berberine (Fig. la). Morphine and codeine are two of the most important analgesics used in medicine, and plants remain the main commercial source of the alkaloids (8). Development of plant cell cultures of Eschscholzia califomica, Papaver somniferum, and Coptis japonica has aided in the isolation and cloning of many enzymes involved in the biosynthesis of isoquinoline alkaloids (9). 

In November 1950,1 studied the effect of bulbocapnine on rats, and published the results in the Archives of Neurology and Psychiatry. Bulbocapnine produces all of the motor manifestations of catatonic schizophrenia in human beings. The drug is an aporphine isoquinoline alkaloid that decreases dopaminergic activity in the brain, and inhibits tyrosine hydroxylase, the rate-limiting enzyme in the catecholamine biosynthesis. 

The biosynthesis of protoberberine alkaloids, including berberine, has been extensively studied, and all the enzymes of the biosynthetic pathway have been characterized (11,121,391,508). Interestingly the pathway leading to berberine in Berberis was found to be different from that in Coptis and Thalictrum (509). In the former species berberine is formed from columbamine, in the latter plant species from tetrahydroberberine (121). The production of isoquinoline alkaloids, including the protoberberine alkaloids, by plant cell cultures have been reviewed by Riiffer (390) and Ikuta (510). Table XXVI summarizes patents concerning the production of berberine by means of plant cell cultures. In Table XXVII a summary is given of the occurrence of berberine in some plant cell cultures. 

The terpenoid indole alkaloids are a group of plant bases derived by multiple variation on the strictosidine [(79) p. 20] skeleton. Arguably the most important work in the past five years has been done on these alkaloids with enzyme preparations from plant tissue cultures, and the research is of great potential significance for other studies in alkaloid biosynthesis. The results have allowed close definition of the early stages of biosynthesis (this Report, p. 19). Use of crude enzyme preparations in this way has been extended to the study of benzylisoquinoline biosynthesis, with enzyme-catalysed formation of norlaudanosoline-1-carboxylic acid [(57) p. 16] this compound had earlier been identified as the first of the benzylisoquinolines (this Report, p. 15). It seems that amino-acids of this general formula (6) are key intermediates in the biosynthesis of all isoquinoline alkaloids. Lophocereine (7) is exceptional in that two routes (from leucine and mevalonate) may lead to it, only one of which potentially involves an acid like (6). ... 

Fig. 2. Alkaloid biosynthetic pathways are associated with a diverse variety of cell types. The tissue-specific localization (shaded) of enzymes and/or gene transcripts are depicted for the biosynthesis of tropane alkaloids in Atropa belladonna and Hyoscyamus niger roots (A), monoterpenoid indole alkaloids in Catharanthus roseus leaves (B), pyrrolizidine alkaloids in Senecio vernalis roots (C), pyrrolizidine alkaloids in Eupatorium cannabinum roots (D), benzyl-isoquinoline alkaloids in Papaver somniferum vascular bundles (E), and protoberberine alkaloids in Thalictrwn flamtm roots (F).

Table 15.2 Details of KEGG patliway and enzyme name and equation catalyzed by the enzyme during the biosynthesis of isoquinoline alkaloids ...

Table 15.4 Predicted orthologs of isoquinoline alkaloid biosynthesis pathway enzymes (benzylisoquinoline) in other plants ...

Table 15.5 Details of enzymes detected for oithologs in other plants related to isoquinoline alkaloid biosynthesis pathway ...

Reticuline oxidase BBE berberine bridge enzyme berberine-bridge-forming enzyme tetrahydroprotoberberine synthase oxidoreductases Isoquinoline alkaloid biosynthesis (m00950)... 

The biosynthesis of the various isoquinolines is reviewed in two chapters, one devoted solely to the morphinans and the other to the other skeletal types. Attempts to produce morphinan alkaloids by plant cell culture techniques has produced a flurry of activity in several laboratories throu out the world. Four chapters are concerned with plant cell culture techniques for the production of isoquinolines. A series of enzymes which catalyse specific steps in isoquinoline alkaloid biosynthesis have been isolated in recent years and the stage is now set for the isolation and characterization of the enzymes responsible for morphinan alkaloid biosynthesis. The utilization of these enzymes for biotechnological conversions is now envisaged. 

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