Cadaverine-Pyruvate Transamination: the Principal Step of Enzymatic Quinolizidine Alkaloid Biosynthesis in L Upia’Us Pol Yphyll Us Cell Suspension Cultures
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Volume 101, number 2 FEBS LETTERS May 1979 CADAVERINE-PYRUVATE TRANSAMINATION: THE PRINCIPAL STEP OF ENZYMATIC QUINOLIZIDINE ALKALOID BIOSYNTHESIS IN L UPIA’US POL YPHYLL US CELL SUSPENSION CULTURES Michael WINK and Thomas HARTMANN Institut fiir Pharmazeutische Biologic der Technischen Universitit, Braunschrveig, O-3300 Braunsclzwei~, FRG Received 12 March 1979 1. Introduction 1 mM dithioerythritol and stirred in an ice bath for 30 min. The pellet, recovered by centrifugation, was In vivo incorporation experiments with labelled resuspended in buffer. The standard reaction mixture precursors have established that the quinolizidine (total vol. 5 ml; radioactive assays 2 ml) consisted of: alkaloids are derived from lysine, via its decarboxyla- the enzyme-buffer suspension (corresponding to tion product cadaverine [l-3]. Free intermediates -200 mg acetone powder), 5 mM cadaverine, 10 mM between cadaverine and the tetracyclic alkaloids pyruvate, 10 mM diethyldithiocarbamate (DIECA). have not been detected so far. Several hypothetical The reaction vessels were gassed with N2 for 1 min, mechanisms have been proposed for the pathway thoroughly sealed and shaken for 3-5 h in the dark. leading from cadaverine to lupine alkaloids [ 1,3,4]. The reaction was terminated with trichloroacetic acid Some authors have suggested that diamine oxidase, and the precipitate was removed by centrifugation. which is known for alkaloid producing plants, also The total alkaloid content of the enzymatic assays might be involved in the synthesis of lupine alkaloids was determined photometrically with modified [3,5-71. Reifer’s reagent [8] at 830 mn. The extinction was Here we report the transamination of cadaverine linear over l-10 pg alkaloid/ml. Sparteine was as the principal step in the enzymatic synthesis of chosen as a standard. tetracyclic alkaloids, catalyzed by a crude enzyme Thin-layer chromatographic separation of alkaloid system prepared from Lupinus polyphyllus cell sus- mixtures and cadaverine was on silica-gel HF-256 pension cultures. (Merck, Darmstadt) with the solvents: I, cyclohexane/ diethylamine (7/3); II, methylene chloride/methanol/ NH3 (80/20/l); detection, Dragendorffs reagent. 2. Materials and methods Gas-liquid chromatographic separation of lupine alkaloids was with a Perkin-Elmer gas chromatograph Cell suspension cultures of L. polyphyllus were (F 22) equipped with capillary columns and flame grown in a modified MS medium at 25°C under ionisation and nitrogen detectors. Gas-liquid chro- continuous illumination as shake cultures or as semi- matography/mass spectroscopy was carried out using continuous fermenter cultures. Cells were harvested a Perkin-Elmer GC/AEI MS 30 combination. Identifi- in the stationary growth phase and homogenized in cation of reference alkaloids isolated by preparative cold acetone (-20°C). Dried acetone powders were layer chromatography from plant extracts was stored at -20°C. performed by mass spectroscopy (AEI MS 9). Acetone powder (5 g) was suspended in 100 ml [ 14C]alanine and [ 14C]pyruvate were isolated from 0.05 M sodium-phosphate buffer (pH 7.8) containing enzyme assays by ion-exchange chromatography ElsevierjNorth-Holland Biomedical Press 343 Volume 101, number 2 FEBS LETTERS May 1979 (Amberlite-IR-120) according to [9]. [2,5-‘4C]cadav- Table 2 erine was purchased from NEN and [U-‘4C]pyruvate Diamine oxidase activity in acetone powder preparations from Buchler/Amersham. from I,. polyphyllus plants and P. sativum seedlings Assay Diamine oxidase act. (% control) 3. Results L. polyphyllus P. sativum The alkaloid content of L. poZyphyZZus cell sus- Complete (control) 100 100 N,-atmosphere pension cultures (“5 pg/g fresh wt) is -500-times 28 30 plus 1 mM DIECA 14 48 lower than in the differentiated plant. It can be raised plus 10 mM DIECA 0 0 however, when cadaverine is fed to the cultures. Thus the presence of an alkaloid synthesizing enzyme Enzyme activity was determined according to [ 111 system is indicated. Enzyme preparations of cell cul- tures offer the advantage that background alkaloid tion by pyruvate suggests that a transamination of content cannot interfere with the quantification of cadaverine is involved. To prove this an enzyme enzymatically produced alkaloids. preparation was incubated with 3 mM [‘4C]pyruvate Crude insoluble enzyme preparations synthesize (1 @i) and 3 mM cadaverine. The only labelled alkaloids from cadaverine in the presence of pyruvate compound which could be identified in the amino (table 1). The activity could be increased by the acid fraction was alanine. The correlation between exclusion of oxygen during incubation. Therefore a alanine formation and cadaverine transformation was participation of diamine oxidase in alkaloid biosyn- followed in experiments in which either pyruvate or thesis is unlikely. This could be proven in experiments cadaverine served as labelled precursor. A positive with the diamine oxidase inhibitor DIECA [lo]. correlation between the rates of net transamination Diamine oxidase activity in enzyme preparations of and cadaverine transformation can be established L. poZyphyZZus and Pisum sativum (as a reference) is (fig.1). Both rates are of the same order, since no totally inhibited in the presence of 10 mM DIECA significant difference could be calculated using the (table 2) whereas alkaloid synthesis is even increased Wilcoxon matched pairs signed rank test of the Dixon- (table 1). Mood test. The activation of the enzymatic alkaloid forma- Furthermore carbonyl reagents (10 mM each) as semicarbazid, cyanide or hydroxylamine, which are Table 1 known to interact with pyridoxal phosphate-depen- Conditions of alkaloid production from cadaverine by an dent enzymes cause 85-95% inhibition of both enzyme preparation from L. polyplzyllus cell cultures pyruvate-cadaverine transamination and alkaloid production. Assay Total alkaloid Under physiological conditions 5-aminopentanal, produced (70) the deamination product of cadaverine, undergoes Complete (standard assay) 100 spontaneous cyclization to A’-piperideine. Piperideine minus pyruvate 10 forms an orange-coloured adduct with o-amino- minus pyruvate benzaldehyde which can be measured photometrically plus 2-oxoglutarate 20 at 435 nm [l 11. In fact this method was employed to minus DIECA 58 in presence of air 42 determine diamine oxidase activity (table 2). boiled enzyme < 5 However, when o-aminobenzaldehyde was added to actively transaminating assays the formation of the Enzymatic incubation was performed under standard assay coloured adduct could never be detected. conditions, Total alkaloids were determined with modified The pH optimum for the alkaloid production was Reifer’s reagent. At least 2 trials were performed for each 7.8. The reaction was found to be linear with time for assay. All values were corrected by blank activity (without added cadaverine). Complete assays produced G 14 ~g alka- > 5 h. An app. Km 0.3-0.8 mM has been calculated loids/5 h and 100 mg acetone powder for cadaverine. Addition of pyridoxal phosphate did 344 Volume 101, number 2 I:EBS LETTERS May 1979 spectroscopy. As the main product a tetracyclic alkaloid of the oxosparteine type (M’ m/z 248) [ 121 could be identified, which presumably corresponds to peak I of fig.2A. The structural identification of all reaction products will be presented elsewhere. There is no indication so far, that tetrahydroanabasine or tripiperidine, which are known to be formed sponta- neously from A’-piperideine are present in the enzyme incubation mixtures. I A I cadaverme 10 20 % net transamination of pyruvate Fig.1, Correlation between the rates of pyruvate transamina- tion and cadavcrine transformation. Enzymatic incubations were performed under standard assay conditions with 3 mM cadaverine and 3 mM pyruvate using various enzyme prepara- tions of different age and origin. In each expcrimcntal set one sample contained 1 &‘i [‘4C]pyruvatc (total transamina- tion) and a corresponding sample 1 PCi [“‘Clcadaverine (cadavcrine transformation). Net transamination was calculated from the produced [‘4C]alanine minus background activity ([‘4C]alanine produced in controls without added cadaverine; -5% total activity). For the calculation of cadaverine trans- formation the reaction mixture (300 ~1) was separated by c-Jgxl@@ thin-layer chromatography. The cadaverine and alkaloid I 0 2 0 3 zones were localized by radioscanning, scraped off the plates, eluted with acidified 70% methanol and measured by scin- tillation counting. The regression follows the equation: Y = 0.99 + 1.017 (x);p < 0.001. not influence enzyme activity. During storage of Pig.2. Thin-layer chromatographic separation of the enzyma- acetone powders at -2O”C, -80% of enzyme activity tically formed products from [“‘C]cadaverinc. Enzymatic is lost within 3 months. incubation was performed under standard assay conditions with 1 mM [‘4C]cadaverine (5 PCi) and 3 mM pyruvate. The In fig.2A thin-layer chromatographic separation of alcalized reaction mixture was extracted with methylene the reaction products of enzymatic [ “C]cadaverine chloride dried over Na,SCI,, concentrated and co-chromato- transformation is illustrated. In both solvent systems graphed (solvent I) with the known alkaloid mixture obtained identical RF-values were found for some of the radio- from I,. po[yphyll~rs. (A) Radioactive spots detected by active spots and authentic tetracyclic lupine alkaloids