Alkaloids lysine decarboxylase

The enzyme, i.e. lysine decarboxylase, that is required for the conversion of lysine into cadaverine, and thus the first step of alkaloid biosynthesis, has been isolated from chloroplasts of L. polyphyllus,28 Like the majority of amino-acid decarboxylases, this enzyme is dependent on pyridoxal 5 phosphate. Its activity was found not to be affected by the presence or absence of quinolizidine alkaloids. Control of the enzyme by simple product feedback inhibition therefore seems unlikely. The operational parameters of this enzyme resemble those of the 17-oxosparteine synthase. Co-operation between the two enzymes would explain why cadaverine is almost undetectable in vivo. 

Alkaloid metabolism in lupine was proved by Wink and Hartmann to be associated with chloroplasts (34). A series of enzymes involved in the biosynthesis of lupine alkaloids were localized in chloroplasts isolated from leaves of Lupinus polyphylls and seedlings of L. albus by differential centrifugation. They proposed a pathway for the biosynthesis of lupanine via conversion of exogenous 17-oxosparteine to lupanine with intact chloroplasts. The biosynthetic pathway of lupinine was also studied by Wink and Hartmann (35). Two enzymes involved in the biosynthesis of alkaloids, namely, lysine decarboxylase and 17-oxosparteine synthetase, were found in the chloroplast stoma. The activities of the two enzymes were as low as one-thousandth that of diaminopimelate decarboxylase, an enzyme involved in the biosynthetic pathway from lysine to diaminopimelate. It was suggested that these differences are not caused by substrate availability (e,g., lysine concentration) as a critical factor in the synthesis of alkaloids. Feedback inhibition would play a major role in the regulation of amino acid biosynthesis but not in the control of alkaloid formation. 

If instead of protonation of the imine function in (14), in the lysine decarboxylase reaction, nucleophilic attack by the 6-amino-group of lysine [see (19)] occurs, (16) is obtained directly and independently of cadaverine, and without loss of the C-2 proton of lysine. This modified" decarboxylase would function, it is suggested, for the biosynthesis of alkaloids such Lysine decarboxylase... 

There is an alternative way of viewing the above results, however. It could be that the biosynthetic pathway to the pyrrolidine ring of nicotine is similar (in part) to the route to the piperidine alkaloids. Part of the model suggested for the biosynthesis of the piperidine nucleus from lysine (see above) could be easily adapted to account for the C02 and nornicotine results, that is variable/in-complete equilibration of bound putrescine (arising by enzyme-mediated decarboxylation of ornithine) with unbound material. L-Ornithine decarboxylase (EC 4.1.1.17, L-ornithine carboxy-lyase) occurs widely in higher plants and like L-lysine decarboxylase requires pyridoxal phosphate as a co-factor. ... 

The conversion of lysine into piperidine alkaloids involves retention of hydrogen isotope at C-2/° The sequence is suggested to be that shown in Scheme 1, and catalysis of the reaction may be attributed to L-lysine decarboxylase. This enzyme, from the micro-organism Bacillus cadaveris, has been found to carry out the conversion of L-lysine into cadaverine with retention of configuration. Decarboxylation of L-[2- H]lysine by this enzyme then affords [15- H]-cadaverine. When this material is converted into alkaloids, e.g. iV-methyl-pelletierine (4 R = Me), the tritium attached to what becomes C-2 is lost cf. refs. 5 and 6. On the other hand, conversion of lysine into sedamine (27) in Sedum acre results in retention of the tritium originally present at C-2. The simplest explanation is that protonation of (26) in the micro-organism and plant proceeds with opposite stereochemistry. This is at variance, however, with current ideas on the stereochemistry of reactions that are catalysed by pyridoxal phosphate. ... 

This is disturbing, and so the stereochemistry of the overall reaction L-lysinecadaverineA -piperideine has been checked, using L-lysine decarboxylase from Escherichia coli and B. cadaveris, pea seedling diamine oxidase, and 5. acre plants, with confirmation of the above deductions the lysine decarboxylase from the two sources effected decarboxylation with the same stereochemical outcome. Solution of the problem must now await further experiments with the enzymes involved in alkaloid biosynthesis. 

The biochemistry and molecular biology of quinolizidine alkaloid biosynthesis have not been fully characterized. Quinolizidine alkaloids are formed from lysine via lysine decarboxylase (LDC), where cadaverine is the first detectable intermediate (Scheme 6). Biosynthesis of the quinolizidine ring is thought to arise from the cyclization of cadaverine units via an enzyme-bound intermediate 176). LDC and the quinolizidine skeleton-forming enzyme have been detected in chlorop-lasts of L. polyphyllus 177). Once the quinolizidine skeleton has been formed, it is modified by dehydrogenation, hydroxylation, or esterification to generate the diverse array of alkaloid products. 

Scheme 6. Biosynthesis of the quinolizidine alkaloids (+ )-4-coumaroylepilupinine and (-)-13a-tigloyloxymultiflorine. Molecular clones have been isolated for the enzymes shown. Abbreviations ECT,/7-coumaroyl-coenzymeA ( + )-epilupinine 0-/ -coumaroyltransferase HMT/HLT, tigloyl-coenzymeA (-)-13a-hydroxymultiflorine/( +)-13a-hydroxylupanine 0-tigloyltransferase LDC, lysine decarboxylase.

Quinolizidine alkaloids are derived from lysine. Studies with labeled precursors indicate that a symmetrical intermediate, cadaverine (20), is involved in their formation (Herbert, 1988 Kinghom and Balandrin, 1984 Leete, 1983 Spenser, 1985), although no intermediate comparable to the dimeric form plays a role in the formation of pyrrolizidine alkaloids is involved (Spenser, 1985). Much recent information is based on cell suspension cultures of Lupinus polyphyllus, Baptisia australis, and Sarothamnus scoparius (all Faba-ceae). Lysine decarboxylase is localized in leaf chloroplasts (Wink 1987 Wink and Hartmann, 1982,1984) the presence of a diamine oxidase does not appear to be involved. Lysine decarboxylase is found in all parts of Lupinus plants. 

In general, alkaloids derive from the metabohsm of amino acids such as phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp), omitine (Om), or lysine (Lys). Quinolizidine alkaloids derived from L-lysine. Its decarboxylation by means of the enzyme lysine decarboxylase gives cadaverine (Cad), the first detectable intermediate of this biosynthetic pathway (Scheme 14.1). 

Bunsupa S, Katayama K, Dcerrra E, Oikawa A, Toyooka K, Saito K, Yamazaki M (2012) Lysine decarboxylase catalyzes the first step of quinolizidine alkaloid biosynthesis and coevolved with alkaloid production in leguminosae. Plant Cell 24 1202-1216 Facchini PJ (2001) Alkaloid biosynthesis in plants biochemistry, cell biology, molecular regulation, and metabolic engineering applications. Annu Rev Plant Physiol Plant Mol Biol 52 29-66... 

The first step in the biosynthesis of piperidine, quinoli-zidine, and lycopodium alkaloids is the PLP-assisted decarboxylation of L-Lys to the diamine cadaverine (38) by lysine decarboxylase (EC 4.1.1.18) (Scheme 11.5) [9, 27]. Similar to putrescine, this foul-smelling compound is associated with putrefying animal tissue as one might expect by hearing its name. Next, oxidative deamination of cadaverine by copper amine oxidase (EC 1.4.1.22) yields 5-aminopentanal... 

Enzymes of Quinolizidine Alkaloid Biosynthesis.- In the past four years Hartmann, Wink, and their coworkers have obtained enzymes from Lupinus (especially L.polyphyllus) species which catalyse the formation of the tetracyclic quinolizidine alkaloids such as sparteine and lupanine from lysine. A novel biogenetic scheme has been proposed which accommodates these new results, and is consistent with previous biosynthetic studies on these alkaloids in intact plants . This new hypothesis (with some minor modifications by this reporter) is illustrated in Scheme 4. The first step in this sequence is the decarboxylation of lysine to yield cadaverine (38). This lysine decarboxylase was isolated from the chloroplasts of L. polyphyHub lea.ves, It is also present in... 

The lysine decarboxylase from L. polyphyllus had a maximxim activity at pH 8.0, and was not inhibited by the ultimate alkaloids. 

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