Flocculation of algae using chitosan

Flocculation of three freshwater algae, Spirulina,Oscillatoria and Chlorella, and onebrackish alga, Synechocystis, using chitosan was studiedinthe pH range 4 to 9, and chlorophyll-a concentrations inthe range 80 to 800 mg m^–3, which produces aturbidity of 10 to 100 nephelometric turbidity units (NTU) in water. Chitosanreduced the algal content effectively by flocculation and settling. Theflocculation efficiency is very sensitive to pH, and reached a maximum at pH7.0for the freshwater species, but lower for the marine species. The optimalchitosan concentration that is required to effect maximum flocculation dependedon the concentration of alga. Flocculation and settling were faster whenconcentrations of chitosan higher than optimal are used. The settled algalcellsare intact and live, but will not be redispersed by mechanical agitation. Thede-algated water may be reused to produce fresh cultures of algae.     

Cell hydrophobicity of <Emphasis Type="Italic">Pseudomonas</Emphasis> spp. and <Emphasis Type="Italic">Bacillus</Emphasis> spp. bacteria and hydrocarbon biodegradation in the presence of Quillaya saponin

Biodegradation and hydrophobicity of Pseudomonas spp. and Bacillus spp. strains were tested at different concentrations of the biosurfactant Quillaya saponin. A model mixture of hydrocarbon (dodecane and hexadecane) was used for estimating the influence of surfactants on biodegradation. The bacterial adhesion to hydrocarbon method for determination of bacterial cell surface hydrophobicity was exploited. Among the tested bacterial strains the higher hydrophobicity was noticed for Pseudomonas aeruginosa TK. The hydrophobicity of this strain was 84%. The highest hydrocarbon biodegradation was observed for P. aeruginosa TK (49%) and Bacillus subtilis (35%) strains after 7 days of experiments. Generally the addition of Quillaya saponin increased hydrocarbon biodegradation remarkably. The optimal concentration proved to be 80 mg l⁻¹. The degree of hydrocarbon biodegradation was 75% for P. aeruginosa TK after the addition of saponin. However the most significant increase in biodegradation after addition of Quillaya saponin was in the case of P. aeruginosa 25 and Pseudomonas putida (the increase of biodegradation from 21 to 52% and from 31 to 66%, respectively). It is worth mentioning that decrease of hydrophobicity is correlated with the best biodegradation by P. aeruginosa strain. For the remaining strains, no significant hydrophobicity changes in relation to the system without surfactant were noticed.     

Krill diet affects faecal string settling

Summary Free-floating sediment traps used on a transect from Scotia Sea to Weddell Sea collected larger, more degraded, krill faecal strings in the deeper (150 m) than in the 50 or 75 m traps. The smallest faecal strings were only present in the shallower traps. Sinking velocity of smaller faecal strings was — as expected — much lower than for larger ones, with a total range of 50 to 800 m · day ^–1 for faecal string volumes of 0.007 to 0.53 mm³. Krill feeding largely on diatoms produced faeces with higher settling velocity than those feeding on non-diatom phytoplankton. Smaller krill faecal strings do not leave the upper mixed layer. Potential settling velocities as measured in settling tubes (without turbulence), may in this respect be misleading. Small oval faecal pellets of unknown origin showed relatively high settling velocities (80 to 250 m·day^–1 for 0.002 to 0.013 mm³) due to higher compaction and lower form resistance to sinking.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Variation in the Settling Velocity of Suspended Particulate Matter in Shallow Lakes,with Special Implications for Mass Balance Modelling

Measurements of sedimentation were combined with water samples to calculate settling velocity of suspended particulate matter (SPM) in lakes. The study sites were open water stations and enclosures in Lake Erken (Sweden) and Lake Balaton (Hungary). Settling velocities were found to vary considerably both inside and outside the enclosures. Within sites, the differences between 25th and 75th percentiles of measured settling velocities of SPM were two‐ or three‐fold. Median settling velocities of SPM ranged from around 0.5 m/d in the enclosures of Lake Erken to more than 8 m/d in the open water of Lake Balaton. Special relevance was attributed to flocculation, which is known to be affected by, e.g., SPM concentration and turbulence. Even though not directly measured, the less turbulent environment inside the enclosures was suggested to explain the low settling velocity compared to the open water environment. Settling velocity apparently correlated with water current speed (r² = 0.66; n = 12). Stepwise multiple linear regressions were used to relate the variability in settling velocity of SPM to the variability of possible controlling factors in a number of data subsets. In most cases, one variable describing the total amount of settling material (e.g., SPM) and one variable reflecting the composition of settling material (e.g., total phosphorus) were chosen. The use of suspended solids concentration to predict settling velocity in mass balance models was discussed. It was found that the mean slope between SPM and v_SPM was close to 0.1 (m⁴d^–1 g^–1). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Relation between Candida maltosa Hydrophobicity and Hydrocarbon Biodegradation

Summary The growth of Candida maltosa on hydrocarbons (dodecane and hexadecane) was influenced by adding various natural and synthetic surfactants. Microbial adhesion to the hydrocarbon was used to measure the surface cell hydrophobicity of the yeast, which in the presence of a synthetic surfactant correlated with the degree of hydrocarbon biodegradation. Non-ionic surfactants caused the highest degree of hydrocarbon biodegradation corresponding the lowest hydrophobicity. A different correlation was observed with natural surfactants, of which saponin was the most effective for hydrocarbon biodegradation, though the concentration of this surfactant had no influence on surface cell hydrophobicity.     

A method for measuring the settling velocity distribution of large biotic particles

A simple method for measuring the settling velocity (V _s) distribution of pollen and spores 30–100 μm in diameter is detailed and evaluated. The method is called the ‘settling tower' and consists in taking sequential pictures of particles falling under gravity in calm air. The scene is illuminated by a cold light source, while a camera takes 15 pictures per second. Between 20,000 and 100,000 images are analysed to obtain the distribution of V _s for a given set of particles. The method was validated using two standard particles with mean diameters of 68 and 108 μm, respectively, as well as Lycopodium spores, with a mean diameter of 35 μm. For each set of particles, the theoretical V _s distribution was estimated from the particle diameter distribution and the volumetric mass using a non-Stokian law, as the Reynolds numbers of the particles were large. The mean V _s was measured with the ‘settling tower' with less than 12% error, while the standard deviation of the V _s distribution was estimated with less than 51% error. The maximum error on the mean V _s was 12% for the Lycopodium spores and less than 2% for the two larger particles. The mean V _s of Lycopodium spores was 4.2 cm s⁻¹, and its standard deviation was 0.7 cm s⁻¹. The reason for the small overestimation of V _s for Lycopodium spores by the ‘settling tower' method is discussed. Preliminary measurements shows that, the ‘settling tower' could be of great practical interest for measuring the distribution of V _s of maize pollen as well as other types of pollen or spores.     

Parameters influencing asymmetric synthesis of (R)-mandelonitrile by a novel (R)-hydroxynitrile lyase from Eriobotrya japonica

(R)-Mandelonitrile was successfully synthesized by an enzymatic transcyanation reaction of benzaldehyde and acetone cyanohydrin catalyzed by a hydroxynitrile lyase from Eriobotrya japonica (EjHNL) in an aqueous-organic biphasic system. The effects of pH, temperature, organic solvent, substrate concentration and enzyme concentration on the initial activity and enantioselectivity of the enzyme were studied. Both pH and temperature had a large effect on the initial velocity and enantiomeric excess (e.e.) of the product, (R)-mandelonitrile. High enantiomeric purity of the product was observed at low pH and temperature because the non-enzymatic reaction producing racemates of mandelonitrile was almost suppressed. The optimum pH and temperature to obtain high e.e. were pH 4.0 and 10 °C, respectively. Surprisingly, the organic solvents had a significant influence on the initial velocity of the reaction but less influence on the enantiomeric purity of product. The EjHNL was very stable in ethyl acetate, diethyl ether, methyl-t-butyl ether, diisopropyl ether, dibutyl ether and hexane for 12 h. The best solvent for the highest initial velocity and e.e. was diethyl ether with an optimum aqueous phase content of 50% (v/v). The initial reaction rate increase as the aqueous phase content rose, but when the content was more than 50%, a reduction of e.e. was observed. Increasing the concentration of the substrates accelerated the initial velocity, but caused a slight decrease in the e.e. of the product. Under the optimized conditions, the conversion and e.e. of (R)-mandelonitrile for 3 h were 40 and 99%, respectively. The aqueous phase containing the enzyme also showed considerably efficient reusability for 4 batch reactions.     

Synthesis, characterization, and antibacterial activity of N,O-quaternary ammonium chitosan

N,N,N-Trimethyl O-(2-hydroxy-3-trimethylammonium propyl) chitosans (TMHTMAPC) with different degrees of O-substitution were synthesized by reacting O-methyl-free N,N,N-trimethyl chitosan (TMC) with 3-chloro-2-hydroxy-propyl trimethyl ammonium chloride (CHPTMAC). The products were characterized by ¹H NMR, FTIR and TGA, and investigated for antibacterial activity against Staphylococcus aureus and Escherichia coli under weakly acidic (pH 5.5) and weakly basic (pH 7.2) conditions. TMHTMAPC exhibited enhanced antibacterial activity compared with TMC, and the activity of TMHTMAPC increased with an increase in the degree of substitution. Divalent cations (Ba²⁺ and Ca²⁺) strongly reduced the antibacterial activity of chitosan, O-carboxymethyl chitosan and N,N,N-trimethyl-O-carboxymethyl chitosan, but the repression on the antibacterial activity of TMC and TMHTMAPC was weaker. This indicates that the free amino group on chitosan backbone is the main functional group interacting with divalent cations. The existence of 100 mM Na⁺ slightly reduced the antibacterial activity of both chitosan and its derivatives.     

Functional Characteristics of Pyruvate Transport inPhycomyces blakesleeanus

Jesús A. Marcos, Dolores de Arriaga, Félix Busto, and Joaquín Soler¹1997. Functional Characteristics of Pyruvate Transport inPhycomyces blakesleeanus. Fungal Genetics Biology25, 204-215. A saturable and accumulative transport system for pyruvate has been detected inPhycomyces blakesleeanusNRRL 1555(−) mycelium. It was strongly inhibited by α-cyano-4-hydroxycinnamate. -Lactate and acetate were competitive inhibitors of pyruvate transport. The initial pyruvate uptake velocity and accumulation ratio was dependent on the external pH. TheV_maxof transport greatly decreased with increasing pH, whereas the affinity of the carrier for pyruvate was not affected. The pyruvate transport system mediated its homologous exchange, which was essentially pH independent, and efflux, which increased with increasing external pH. The uptake of pyruvate was energy dependent and was strongly inhibited by inhibitors of oxidative phosphorylation and of the formation of proton gradients. Glucose counteracted the inhibitory effect of the pyruvate transport produced by inhibitors of mitochondrial ATP synthesis. Our results are consistent with a pyruvate/proton cotransport inP. blakesleeanusprobably driven by an electrochemical gradient of H⁺generated by a plasma membrane H⁺-ATPase.     

Inducing autoflocculation in the diatom <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis> through CO<Subscript>2</Subscript> regulation

The effect of pH on flocculation was studied using the diatom Phaeodactylum tricornutum and the green algae Scenedesmus cf. obliquus as surrogate species. There was a distinct, species-specific threshold of pH where flocculation started. P. tricornutum started to flocculate at pH 10.5 and S. cf. obliquus at pH 11.3. Above this threshold, settling rates up to 360 cm h⁻¹ were observed for P. tricornutum and the concentrating factor was up to 60-fold. The combined effect of pH, turbulence, and cell density on flocculation of P. tricornutum was additionally studied in a factorial 5³-design experiment. pH was the most important factor affecting flocculation, but at the pH threshold (pH 10.5), the concentrating factor was increased by increasing cell density and turbulence. Algae increases the pH during photosynthesis, and the P. tricornutum and S. cf. obliquus cultures increased the pH to a maximum of 10.8 and 9.5, respectively, after discontinuing the CO₂ supply. For P. tricornutum, this was above the flocculation threshold, and rapid settling of this species due to increased pH was observed in a matter of hours after the CO₂ supply was turned off. This could be used as a simple, low-cost, initial dewatering step for this species.     

Changes in haemolymph ion concentrations of Astacus astacus L. and Pacifastacus leniusculus (Dana) after exposure to low pH and aluminium

During exposure to soft water, acidified to pH 4.0, the haemolymph concentrations of Na⁺, K⁺, and Cl^– decreased whereas the Ca²⁺ concentration fluctuated in Astacus astacus. The haemocyte content of K⁺ decreased from 9% to 2% of the total haemolymph K⁺ content after exposure to pH 3.7 for 3 days. Within 14 days, 250 µg Al³⁺ l^–1, as Al₂(SO₄)₃ at pH 5.0, reduced the haemolymph Na⁺ content in Astacus astacus and Pacifastacus leniusculus, however, the effects were less pronounced than earlier reported for fish. Disturbed ion regulation, mainly depending on low pH, is thought to contribute to the absence of these species in acid waters.     

Evidence for a plasmalemma-based CO2 concentrating mechanism in Laminaria saccharina

A kinetic analysis of the photosynthesis inhibition by buffers allowed quantification of some components of the carbon concentrating mechanism (CCM) of the brown macroalga Laminaria saccharina. The CCM was based on the presence of acid regions outside the plasma membrane that increased the CO₂ concentration available for photosynthesis by 10–20 times above that of the bulk medium at alkaline pH. Furthermore, the results suggested that the CCM is located mainly on the cell membrane and not in the chloroplast, as suggested for most macroalgae. The degree of dissipation of the acid regions by a buffer was related to the buffer anion concentration (B⁻), estimated from the titration of the buffer from bulk medium pH to a pH endpoint value close to the first pK _a of the carbonic acid system. A kinetic model describing the relationship between inhibition of photosynthesis by a buffer and B⁻ was developed suggesting that buffers act as competitive inhibitors with IC₅₀ (the concentration of the buffer anion which reduces the reaction velocity by half) of 5.0 mol m⁻³. This model can be used to estimate the inhibitory effect of any buffer on the photosynthesis of L. saccharina. Nevertheless, some buffers tested showed a lower effect than that predicted from the hyperbolic model suggesting that their strength as inhibitors depended on: (1) the pK _a in relation to the first pK _a of the carbonic acid system and (2) its molecular weight (i.e. its mobility).     

贝类壳-体质量比和静水沉降特性的相关性

软体动物贝壳表型是适应性进化的结果,为探究贝壳形态特性与软体动物随水流扩散功能的相关性,实验选取9种具代表性的腹足纲和双壳纲贝类作为研究对象,研究了其成体的壳-体质量比与静水沉降特性及二者的相关性。结果表明：体质量的变异系数（C.V.=1.11）大于壳长（C.V.=0.67）、壳宽（C.V.=0.54）的变异系数;壳-体质量比具较强的种属特异性,种内变异系数小（C.V.=0.20）,而种间差异极显著（P < 0.01）。受试贝类的平均壳-体质量比为0.32±0.13,陆生贝类的壳-体质量比显著小于水生贝类（P < 0.01）,壳-体质量比最大的河蚬（0.54±0.06）是最小的非洲大蜗牛（0.17±0.04）的3倍,福寿螺的壳-体质量比为0.50±0.06。双壳类和螺类的沉降行为差异明显,只有中华园田螺、铜锈环棱螺和河蚬不能在静水中漂浮;沉降速度最大的河蚬（（24.99±4.22）cm/s）是最小的椭圆萝卜螺（（4.13±0.96）cm/s）的6倍,入侵种非洲大蜗牛（（18.30±3.64）cm/s）和福寿螺（（21.77±5.23）cm/s）与土著种铜锈环棱螺（（19.48±3.14）cm/s）和中华园田螺（（21.44±3.92）cm/s）在沉降速度上无显著差异（P < 0.01）。成体贝类的壳-体质量比与沉降速度（R²=0.28）、沉降加速度（R²=0.39）之间存在一定的相关性。在此基础上,贝类沉降特性随生活史变化的研究将进一步揭示贝类进化与种群扩散中的生态水力学作用。     

Interactions between a soil fungus,Trichoderma harzianum,and IIb metals—adsorption to mycelium and production of complexing metabolites

Fungi are capable of accumulating metals and, in soil, such accumulation may influence metal speciation and transport. The interactions between a common soil fungus, Trichoderma harzianum, and IIb elements were studied in the present investigation. The accumulation of the metals zinc, cadmium and mercury by starved and non-starved mycelium at different pH was determined by a batch technique using radioactive tracers; uptake of the metals was found to be large, with respective distribution coefficients of about 10^3.5, 10^2.5 and 10^4.0 for zinc, cadmium and mercury, respectively. Metal accumulation by a starved system was largely independent of pH in the range 3–9, where in a non-starved system an increased accumulation of zinc (at 10^– m) was observed at low pH (3–5). Potentiometric titrations performed on the two systems revealed significant differences in acid capacities, i.e. values close to zero for the starved system and 500–800 meq kg^– for the non-starved system. The maximum metal uptake was at least 50 mmol kg^– at pH 6.5 (calculated from adsorption isotherms). The present findings suggests that in the non-starved system a metabolite is produced and then released when the pH is within a certain range.     

Lipase-catalyzed kinetic resolution of (R,S)-1-phenylethyl propionate in an enzyme membrane reactor

Enzymatic stereoselective hydrolysis of (R,S)-1-phenylethyl propionate was performed in a stirred tank and in a biphasic enzyme membrane reactor. Lipase from Pseudomonas sp. was proved to be a good enantioselective catalyst for this reaction. The enzyme was covalently immobilized in a porous polyamide membrane (flat sheet as well as hollow-fibres) via glutaraldehyde. An influence of membrane hydrophobicity on reactor performance was observed. Initial lipase activity and productivity in the processes were equal to 1.05 × 10^?4, 1.3 × 10^?5 and 1.0 × 10^?5 mole/(h × mg of enzyme) in the case of native lipase, in the aromatic polyamide hydrophobic membrane reactor and in the hydrophilic polyamide-6 membrane reactor, respectively. The influence of some factors such as temperature, pH, buffer concentration, initial substrate concentration and addition of β-cyclodextrin derivatives on reaction rate and enantioselectivity was investigated and discussed. In the enzyme membrane reactor both organic and aqueous phases circulated countercurrently on both sides of the membrane. At a conversion degree of under 55–60%, pure enantiomer of the remaining ester (i.e. > 98%) was obtained.     

新生婴儿源植物乳杆菌HLPL03的环境耐受性及其代谢功能低聚糖的生物学活性

【目的】解析健康新生婴儿胎便中植物乳杆菌HLPL03的益生功能,评价其环境耐受性及代谢功能低聚糖的生物学活性。【方法】通过耐受胃肠道条件、过氧化氢和抗生素试验,评估植物乳杆菌HLPL03对极端环境的耐受性;利用改良培养基,评价植物乳杆菌HLPL03代谢功能低聚糖的能力;同时,探究功能低聚糖对植物乳杆菌HLPL03抑菌活性、疏水性和黏附能力的影响。【结果】植物乳杆菌HLPL03在pH 2.5条件下培养3 h后,活菌数仍在10⁴ CFU/mL以上;在0.30%胆盐中培养6 h后,活菌数接近10⁷ CFU/mL;在1.0 mmol/L H₂O₂强氧化剂条件下培养6 h,活菌数显著升高(P<0.001);除低聚木糖外,植物乳杆菌HLPL03能代谢多种功能低聚糖,并对常见食源性致病菌具有较强的抑制能力;棉子糖是改善植物乳杆菌HLPL03生物学活性的最佳低聚糖,其能提高菌株表面疏水性达36.1%,且促进菌株在Caco-2细胞上的黏附率由16.78%提高至42.11%。【结论】健康新生婴儿源植物乳杆菌HLPL03具有良好的抗环境胁迫能力,且其生物学活性能被棉子糖等功能低聚糖有效促进,可作为特色乳酸菌进行研究和开发。     

Cell Surface Hydrophobicity as a Pellicle Formation Factor in Film Strain of Saccharomyces

The film strain of Saccharomyces grows through non-film and film stages. The differences in cell surface hydrophobicity were examined at both stages. The degree of hydrophobic was quantitatively determined by comparing distribution ratios of cells between buffered aqueous and organic solvent phases. The cell surface in the film stage was more hydrophobic than that in the non-film stage, whereas the inherent non-film strain of Saccharomyces always showed low hydrophobicity. These results indicate that the change from non-film to film stage was due to a change in cells from hydrophilic to hydrophobic. The effects of growth conditions on hydrophobicity were further examined with the film strain Saccharomyces bayanus. Ethanol as sole carbon source more efficiently increased hydrophobicity than glucose. The increase in hydrophobicity seemed to depend upon respiration accompanying assimilation of ethanol. It was also found that the addition of a limited amount of biotin, as well as higher pH in medium lowered hydrophobicity. Variation in degree of pellicle formation was positively related to that of cell surface hydrophobicity.     

Decrease in nitrate uptake and increase in proton release in zinc deficient cotton,sunflower and buckwheat plants

The effect of varied Zn supply on the pH of the nutrient solution and uptake of cations and anions was studied in cotton (Gossypium hirsutum L.), sunflower (Helianthus annuus L.) and buckwheat (Fagopyrum esculentum Moench) plants grown under controlled environmental conditions in nutrient solutions with nitrate as source of nitrogen. With the appearance of visual Zn deficiency symtoms, the pH of the nutrient solutions decreased from 6 to about 5 whereas the pH increased to about 7 when the plants were adequately supplied with Zn. In Zn deficient plants the pH decrease was associated with a shift in the cation-anion uptake ratio in favour of cation uptake. Of the major ions, uptake of Ca²⁺ and K⁺ was either not affected or only slightly lowered whereas NO₃ ^- uptake was drastically decreased in Zn deficient plants. Although the Zn nutritional status of plants hardly affected the NO₃ ^- concentrations in the plants, the leakage of NO₃ ^- from roots of Zn deficient plants into a diluted CaCl₂ solution was nearly 10 times higher than that of plants adequately supplied with Zn. In contrast to Zn deficiency, Mn deficiency in cotton plants neither affected NO₃ ^- uptake nor the pH of the nutrient solution.The results indicate that, probably as a consequence of the role of Zn in plasma membrane integrity and nitrogen metabolism, when Zn is deficient in dicotyledonous species net uptake of NO₃ ^- is particularly depressed which in turn results in an increase in cation-anion uptake ratio and a corresponding decrease in external pH. The ecological relevance of this rhizosphere acidification is discussed.     

黄河口湿地柽柳灌丛土壤盐渍化特征

为探究黄河三角洲湿地柽柳灌丛下土壤的盐渍化特征,在黄河三角洲国家级自然保护区(37°35''-12''N,118°33''-119°20''E)黄河入海口附近,根据长势基本一致的原则分别在碱蓬群落、柽柳群落和芦苇群落各选3株柽柳,采集柽柳灌丛下土壤样品,分析土壤盐分和盐碱化参数的空间分布以及距基茎不同距离处研究对象(土壤总盐(TS)、电导率(EC)、pH、交换性钠百分率(ESP))和环境因子(Na⁺、K⁺、Ca²⁺、Mg²⁺、Cl^-、HCO₃^-、SO^2-₄)之间的关系。结果表明：(1)研究区土壤为弱碱化盐土,离子含量由高到低依次为Cl^->Na⁺>SO^2-₄ >Ca²⁺>Mg²⁺>HCO^-₃>K⁺。除pH在土壤表层数值最低外,表层土壤TS、EC、ESP和盐分离子大于深层土壤,显示表聚性。(2)土壤盐分和盐碱化参数空间分布总体为：在柽柳基茎周围形成"盐谷"、"碱谷"效应, Na⁺、Mg²⁺、Cl^-表现为"盐谷",K⁺ 、SO^2-₄ 、Ca²⁺ 表现为"盐岛"。(3)在整个土壤剖面中,与TS、EC相关性最强的阴阳离子为Mg²⁺、Cl^-,从灌丛中心到灌丛间裸地Ca²⁺、SO^2-₄与TS、EC的相关性逐渐减弱,Mg²⁺、Cl^-与TS、EC的相关性逐渐增强。Ca²⁺和SO^2-₄与pH表现为较强的负相关性;与ESP相关性最强的阴离子为HCO^-₃,与之相关性最强的阳离子为Na⁺和K⁺,并且Na⁺和K⁺与ESP的相关性表现出从灌丛中心向外逐渐增强。(4)土壤盐渍化主要受控于Na⁺,从灌丛下到灌丛间裸地Cl^-对盐渍化程度的影响逐渐增加,SO^2-₄的影响逐渐降低。     

N-Methylation of quinolizidine alkaloids: an S-adenosyl-l-methionine: cytisine N-methyltransferase from Laburnum anagyroides plants and cell cultures of L. alpinum and Cytisus canariensis

An S-adenosyl-l-methionine (SAM): cytisine N-methyltransferase could be demonstrated in crude enzyme preparations from Laburnum anagyroides plants and cell cultures of L. alpinum and Cytisus canariensis. The transferase specifically catalyzes the transfer of a methyl group from SAM to cytisine. The apparent K_m values are 60 mol l^-1 for cytisine and 17 mol l^-1 for SAM. Other quinolizidine alkaloids, e.g. angustifoline and albine, are N-methylated by only 10–15%. The transferase shows a pH optimum at pH 8.5. It is activated by dithioerythritol and inhibited by thiol reagents and Fe²⁺ and Fe³⁺. The reaction product S-adenosylhomocysteine is a powerful inhibitor of the transferase reaction. Cell cultures of L. alpinum which have an active SAM: cytisine N-methyltransferase and which are able to N-methylate exogenous cytisine in vivo, do not accumulate cytisine or N-methylcytisine to a detectable degree.Abbreviations GLC gas-liquid chromatography - SAM S-adenosylmethionine - TLC thin-layer chromatography