Putrescine A-methyltransferase

Hibi et al. " have reported on putrescine A-methyltransferase isolated from the nicotine biosynthetic pathway coded by cDNA. Recent advances in cell and molecular biology of alkaloid biosynthesis have heightened awareness of the genetic importance. 

Winz, R. A. and Baldwin, I. T. (2001). Molecular interactions between the specialist herbivore Manduca sexta (Lepidoptera, Sphingidae) and its natural host Nicotiana attenuata. IV. Insect-induced ethylene reduces jasmonate-induced nicotine accumulation by regulating putrescine A-methyltransferase transcripts. Plant Physiology 125 2189-2202. 

Putrescine A-methyltransferase (PMT, EC 2.1.1.53) catalyses the first specific step in the biosynthesis of tropane alkaloids, cocaine and nicotine [123]. Putrescine is methylated by PMT via SAM (S-adenosylmethionine) transferring the methyl group from SAM to an amino group of putrescine. Fig. (1). This enzyme has been isolated from roots of both Nicotiana tabacum and D. stramonium [124], and the activity of this enzyme is restricted to the roots of Solanaceous species corroborated by results describing a root pericycle-specific activity in A. belladonna [125]. Nevertheless, more recently, a low mRNA pmt transcript level in leaves of N. tabacum, with a rise in transcript level after mechanical wounding has been detected [126]. 

Mizusaki, S., Y. Tanabe, M. Noguchi, and E. Tamaki Changes in the activities of ornithine decarboxylase, putrescine A-methyltransferase and A-methyl putrescine oxidase in tobacco roots in relation to nicotine biosynthesis Plant Cell Physiol. 14 (1973) 103-110. 

Scheme 3. Biosynthesis of the tropane alkaloids hyoscyamine and scopolamine, the ca-lystegines, and nicotine. Molecular clones have been isolated for the enzymes shown. Abbreviations CYP82E4, nicotine A-demethylase H6H, hyoscyamine 6jS-hydroxylase ODC, ornithine decarboxylase PMT, putrescine A-methyltransferase TR-I, tropinone reductase-I TR-II, tropinone reductase-II.

In instances in which an asymmetric intermediate is involved, methylated and enzyme-bound forms of putrescine have been suggested. The A-methyl groups of A-methylpyr-rolidine are derived from 5-adenosyl-L-methionine (Fig. 29.1) (Geissman and Crout, 1969) and their formation involves putrescine-A -methyltransferase (Leete, 1980,1990). 

The isoquinoline pathway s enzyme orthologs in other plants showed that genes of methyltransferase family such as (R,S)-reticuline 7-0-methyltransferase, coclaurine 4 -0-methyltransferase, (S)-norcoclaurine 6-0-methyltrasferase, columbamine 0-methyltransferase, coclaurine A-methyltransferase, putrescine A-methyltransferase responsible for the production of reticuline, coclaurine, norcoclaurine, columbaine have been reported from Papaver somniferum, Coptis japonica, Thalictrum flavum, Thalictrum tuberosum, Coffea liberica, Cojfea arabica, Cojfea canephora, Nicotiana tabacum. Solarium tuberosum. Datura stramonium, Hyoscyamus niger, and Atropa belladonna. Pathway contains information of about four alkaloids such as dopamine, colchicine, ephedrine, and methamphetamine and identified two missing links. 

The next step, the methylation of putrescine, already belongs to the secondary metabolism and is catalyzed by the first pathway-specific enzyme, putrescine A-methyltransferase (PMT) discovered in tobacco roots (Mizusaki et al. 1971). Its product, A-methylputrescine, represents the direct precursor of 4-methyl-aminobutanal, as was shown by a cell free preparation of tobacco roots. The oxidative deamination of the diamine is catalyzed by A-methylputrescine oxidase, an enzyme of ahigh substrate specificity (Mizusaki etal. 1972). 4-Methy laminobutanal is cyclized spontaneously forming the A-methyl-A -pyrrolinium cation (present as a salt) (Leete 1967). An alternative route has been proposed for the biosynthesis... 

Hibi N, Fujita T, Hatano M, Hashimoto T, Yamada Y (1992) Putrescine A -methyltransferase in cultured roots of Hyoscyamus albus. Plant Physiol 100 826-835 Hicks CS (1936) Observations on the chemistry of rf-nornicotine, an alkaloid of Duboisia hopwoodii. Austral J Exptl Biol Med Sci 14 39-43 Hicks CS, LeMessurier H (1935) Preliminary observations on the chemistry and pharmacology of the alkaloids of Duboisia hopwoodii. Austral J Exptl Biol Med Sci 13 175-188 Hicks CS, Brucke FT, Heuber EF (1935) Pharmacology of Duboisia hopwoodii (rf-nornicotine). 

Putrescine A-methyltransferase (PMT) catalyzes the first committed step in TPA and nicotine biosynthesis, the SAM-dependent... 

Fig. 5 Biosynthetic pathway of nicotine. Unbroken arrows indicate single enzymatic conversions and broken arrows indicate multiple enzymatic conversions. It is not known whether the 7V-methyl-pyrrolinium cation is coupled to nicotinic acid or a derivative of the latter. PMT putrescine A -methyltransferase...

The first committed biosynthetic step toward pyrrolidine and tropane alkaloids involves N-methylation of putrescine to furnish A-methylputrescine (21) by SAM-dependent putrescine A-methyltransferase (EC 2.1.1.53) (Scheme 11.4) [9, 19, 20]. Oxidative deamination by A-methylputrescine oxidase (EC 1.4.3.21) affords 4-methylaminobutanal (22), which spontaneously cyclizes to furnish the corresponding A-methyl-A -pyrrolinium cation (23) via intramolecular Schiff-base formation. Although no enzymes have been identified catalyzing the subsequent biosynthetic steps, from... 

Junker A, Fischer J, Sichhart Y, Brandt W, Drager B (2013) Evolution of the key alkaloid enzyme putrescine A-methyltransferase from spermidine synthase. Front Pltmt Sci 4 260 Kakehi J, Kuwashiro Y, Niitsu M, Takahashi T (2008) Thermospermine is required for stem elongation m Arabidopsis thaliana. Plant Cell Physiol 49 1342-1349 Kakehi J, Kuwashiro Y, Motose H, Igarashi K, Takahashi T (2010) Norspermine substitutes for thermospermine in the control of stem elongation in Arabidopsis thaliana. FEBS Lett 584 3042-3046... 

Stenzel O, Teuber M, Drager B (2006) Putrescine A -methyltransferase in Solanum tuberosum L., a calystegine-forming plant. Planta (Berl) 223 200-212 Steppuhn A, Case K, Krock B et al (2004) Nicotine s defensive function in nature. PLoS Biol... 

Suzuki K, Yamada Y, Hashimoto T (1999a) Expression of Atropa belladonna putrescine A-methyltransferase gene in root pericycle. Plant CeU Physiol 40 289-297 Suzuki K, Yun DY, Chen XY et al (1999b) An Atropa belladonna hyoscyamine 6p-hydroxylase gene is differentially expressed in the root pericycle and anthers. Plrmt Mol Biol 40 141-152 Thompson JE, Hopkins MT, Taylor C et al (2004) Regulation of senescence by eukaryotic trrmsla-tion initiation factor 5A implications for plant growth and development. Trends Plant Sd 9 174-179... 

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