Subcellular localization of enzymes of anthocyanin biosynthesis in protoplasts

Flavanone synthase, chalcone-flavanone isomerase and UDP-glucose; anthocyanidin-3-O-glucosyltransferase activities of protoplasts and subcellular fractions of protoplasts of Hippeastrum and Tulipa were investigated. Subcellular fractions studied were intact vacuoles, cytosol and particulate components of protoplasts less the vacuole. The cytosol fraction had the highest activity of the three enzymes studied. Results similar to those found for Hippeastrum were obtained with fractions from leaves and petals of Tulipa. The increase in flavanone synthase activity in the cytosol fraction from petals of Hippeastrum during development paralleled the increase in anthocyanin content of the petals.     

Origin of nitrogen in the biosynthesis of solanidine by Veratrum grandiflorum

Veratrum plants accumulate verazine as the major alkaloid in the rhizome during the dormant stage 4 months after cold treatment. The quantitative c     

Dormantinol,a possible precursor in solanidine biosynthesis,from budding Veratrum grandiflorum

A new sapogenin, dormantinol, was isolated from budding Veratrum, and identified as (25S)-cholest-5-ene-3β,22α,26-triol by spectral analysis and its synthesis from dormantinone. Cholesterol was also identified in the budding Veratrum.     

Further studies on the role of phenylalanine in gramicidin S biosynthesis by Bacillus brevis

In a chemically defined medium (F4/3) containing fructose, arginine, histidine and methionine, the addition of 0.1% l-phenylalanine to Bacillus brevis ATCC 9999 enhanced growth and gramicidin S (GS) production on both volumetric and specific bases; surprisingly, it decreased the specific activities of the two GS synthetases. Decreased specific activities were observed even when both soluble and particulate GS synthetases were assayed. The decreases were not caused by inhibition or repression by phenylalanine itself but, more probably, by a negative feedback effect of cellular GS on its own synthetases. High concentrations of GS were found to be associated with cells even before the presence of GS in the fermentation broth was detected. These cellular GS concentrations were much higher in fermentations conducted with phenylalanine.     

正交试验法优选超声提取知母皂甙的研究

用正交实验法对知母(Anemarrhena asphodeloides Bge.)中总皂甙的超声提取工艺进行了研究,采用正交表L9(34),以提取剂的体积分数、料液比(mA∶VB)、提取时间以及提取次数为因素,以知母总皂甙元的含量为指标,用紫外分光光度计法进行检测,所得提取液经大孔树脂纯化,得到的最佳提取参数和结果为:以φ(乙醇)=75%的水溶液为提取剂、提取料液比mA∶VB=1∶8、提取次数2次、每次30min,提取率92.8%,纯度91.0%。结果证明了对知母而言,超声提取法是一种提取效率高、操作简便、省时的方法。     

紫杉醇生物合成相关酶类的研究进展

紫杉醇是红豆杉属植物次生代谢产物之一,是近20年来抗癌药物研究领域的重要发现。弄清楚紫杉醇合成途径和相关酶的反应可以从根本上大大提高紫杉醇的产量。综述近几年来紫杉醇生物合成途径中相关酶的研究工作,包括已经得到相应cDNA克隆的紫杉二烯合成酶,细胞色素P450氧化酶和3个紫杉烷的乙酰转移酶,由于GGPP是紫杉醇合成的必需前体,HMGR和GGPP合成酶的相关情况也有简述。     

The pathway of betalain biosynthesis: Effect of cytokinin on enzymic oxidation and hydroxylation of tyrosine in Amaranthus tricolor seedlings

The effect of exogenously added tyrosine or l -3-(3,4-dihydroxyphenyl) alanine on the accumulation of betacyanin in response to cytokinin in Amaranthus tricolor (L.) var. tricolor half-seedlings depends on the age of the seedlings and the treatment of the seedlings prior to induction of pigment by benzyladenine. Neither extracted polyphenol oxidase, peroxidase or tyrosine hydroxylase activity, nor in vivo tyrosine hydroxylation is increased in response to exposure of seedlings to cytokinin. However a small percentage of the polyphenol oxidase activated or unmasked by Triton X-100 treatment of membrane fractions is increased after cytokinin treatment of half-seedlings for 22 h. It is concluded that cytokinin control may be on a multi-enzyme membrane-located complex involving part of the polyphenol oxidase activity of the tissue (possibly an isoenzyme), and that the majority of the polyphenol oxidase activity in Amaranthus is a constitutive membrane enzyme which is not involved in betacyanin synthesis. Although cytokinins do not affect in vivo tyrosine hydroxylation, this activity follows closely the accumulation of betacyanin which is first detectable about 6.5 h after the application of cytokinin. Only a very low level of in vivo hydroxylation can be demonstrated in half-seedlings treated for 6 h either with or without cytokinin but it begins to increase shortly after this time. A large increase in this activity by 16 h (independent of cytokinin) can be almost completely (79%) prevented by chloramphenicol (300 μM) although the drug increases accumulation of betacyanin. At this concentration about 30% of the protein synthesis in inhibited. In vitro tyrosine hydroxylation is, however, not reduced in half-seedlings treated with chloramphenicol during 16 h induction nor is extractable polyphenol oxidase reduced. It is concluded that chloramphenicol is inhibiting the synthesis of some protein essential for in vivo hydroxylation other than the activity measured during in vitro hydroxylation and that the inhibition of synthesis of 79% in vivo hydroxylation still leaves enough activity for maximum betacyanin synthesis.     

化学诱变剂EMS对知母种子萌发的影响

以知母（Anemarrhena asphodeloides）种子为材料,分别采用1%、2%、4%、6%浓度的EMS处理6、8、12和24 h,在恒温培养箱内进行种子萌发实验,研究不同浓度的化学诱变剂甲基磺酸乙酯（ethyl methane sulfonate,EMS）处理对知母种子萌发的影响,筛选适宜的诱变浓度和诱变时间。结果表明：随EMS浓度的增加和处理时间的延长,知母种子发芽率呈现逐渐降低的趋势,以相对发芽率达到半致死浓度为标准,6%EMS浸种12和24 h可作为EMS诱导知母建立突变体库的适宜条件。     

Further studies on the biosynthesis of the avermectins

Summary The biosynthesis of avermectins was studied further inStreptomyces avermitilis MA5502 by feeding experiments with labeled precursors.¹³C-NMR analysis of the compounds biosynthesized from [2-¹³C]acetate, [1,2-¹³C₂]acetate, [3-¹³C]propionate and [2,3-¹³C₂]propionate confirmed that the aglycone of avermectins is made from seven intact acetate and five propionate units. Feeding experiments with [1-¹³C]2-methylbutyrate and [1-¹³C]isobutyrate have shown that 2-methylbutyrate and isobutyrate are immediate precursors of the starter units of the polyketide chains of avermectin a and b components, respectively. The³H/¹⁴C doublelabeling experiments suggest that the two oleandrose moieties are derived from glucose.     

Mechanism of 14β hydroxylation in the biosynthesis of cardenolides: The role of 14β-cholest-5-en-3β-ol

The intermediary role of 14β-cholest-5-en-3β-ol in the biosynthesis of cardenolides in Digitalis lanata was excluded. This rules out one plausi     

真菌中赖氨酸生物合成途径研究进展

本文综述了真菌中赖氨酸的生物合成途径及途径中的关键基因——酵母氨酸脱氢酶基因,详细介绍了赖氨酸从头合成途径,阐述了酵母氨酸脱氢酶的作用机理及理化性质,以期为探索赖氨酸合成途径及途径中的基因提供资料和思路。     

Genetical and biochemical evidence that the hydroxylation pattern of the anthocyanin B-ring in Silene dioica is determined at the p-coumaroyl-coenzyme a stage

In petals of Silene dioica, gene P controls the 3′-hydroxylation of the anthocyanin B-ring and the hydroxylation pattern of the hydroxycinnamoyl acyl group bound to the 4″'-hydroxyl group of rhamnose of anthocyanidin 3-rhamnosyl(1→6)glucoside-5-glucoside. In this paper, experiments are presented which show that gene P is involved in the hydroxylation of p-coumaroyl-CoA to caffeoyl-CoA, which is then used both as a precursor in anthocyanin biosynthesis and as a substrate for the final acylation.     

Anthocyanin biosynthesis in Pisum: Sequence studies in pigment production

The sequence of anthocyanin accumulation during flower development in four flower-colour mutants of Pisum and in Lathyrus odoratus var. Chloe, shows a progression from methylated to unmethylated anthocyanidins, and the replacement of 3-O-rhamnoside by 3-O-sambubioside and 3-O-sophoroside. This behaviour is explained in terms of the activity of gene Cr.     

Stereospecificity of biosynthesis of triterpene alcohols in Calendula officinalis flowers

Flowers of Calendula officinalis were incubated with mevalonic acid doubly labelled with ¹⁴C in position 2 and ³H in positions 2R, 2S, 4R or 5R,S and the [³H/¹⁴C] ratios determined in squalene and pentacylic mono- and dihydroxy-triterpene alcohols and also in some derivatives prepared from the triterpene alcohols. ³H atoms were located in positions 3, 12, 16, 21, 29, 30 of the ursane skeleton, positions 3, 12, 29, 30 of the lupane skeleton and positions 3, 11, 12, 18 of the oleanane skeleton. Stabilization of α- and β-Amyrins, ω-taraxasterol and lupeol occurs with the elimination of a proton from positions 12, 21 and 29 (or 30) respectively. In addition, during hydroxylation of triterpene monols to the corresponding diols a proton is substituted by the hydroxyl group.     

13C-NMR studies on griseofulvin biosynthesis and acetate metabolism in Penicillium patulum

Incorporations of singly and doubly-labelled acetate-[¹³C] into griseofulvin by a mutant strain of Penicillium patulum confirm its origin from simple folding of a single heptaketide chain. An acetate ‘starter’ effect is observed in the ¹³C-NMR spectra of griseofulvin enriched from acetate-[¹³C], and analysis of the ¹³C—¹³C spin—spin couplings observed indicate a rapid metabolic turnover of added acetate. Methyl, but not carboxyl, of acetate is efficiently metabolised into the C₁ pool.     

Recent advances in the role and biosynthesis of ascorbic acid in plants

The past few years have provided many advances in the role and biosynthesis of L -ascorbic acid (AsA) in plants. There is an increasing body of evidence confirming that AsA plays an important role in the detoxification of reactive oxygen species. The role of AsA in photoprotection has been confirmed in vivo with the use of Arabidopsis mutants. A player in the defence against reactive oxygen species, AsA peroxidase, has been extensively studied at the molecular level, and regulation of this key enzymatic activity appears to occur at several levels. As a cofactor in the hydroxylation of prolyl and lysl-residues by peptidyl-prolyl and -lysyl hydroxylases, AsA plays a part in cell wall synthesis, defence, and possibly cell division. The maintenance of reduced levels of AsA appears to be highly regulated, involving the interplay of both monodehydroascorbate and dehydroascorbate reductases and possibly auxin. A major breakthrough in plant AsA biosynthesis has been made recently, and strong biochemical and genetic evidence suggest that GDP-mannose and L -galactose are key substrates. In addition, evidence for an alternative AsA biosynthetic pathway(s) exists and awaits additional scrutiny. Finally, newly described Arabidopsis mutants deficient in AsA will further increase our understanding of AsA biosynthesis     

Studies on the biosynthesis of the carane skeleton

Measurements of isotope ratios in car-3-ene biosynthesized in Pinus sylvestris from (3RS)-mevalonate-[2-¹⁴C,2R-³H₁], and [2-¹⁴C,4R-³H₁] and the corresponding S-epimers and also from geraniol- [¹⁴C,1-³H₂] and nerol-[¹⁴ C,1-³H₂] have shown that the carane skeleton is constructed from its presumed monocyclic precursor with migration of an olefinic bond, together with an unexpected 1,2-shift of a proton to the site of the original double bond. The detailed stereochemistry of the processes allows a two-step mechanism to be inferred for the cyclization in which a bonded intermediate is involved. The conversion of geraniol into nerol (en route to car-3-ene) probably is a redox process with the intermediacy of the corresponding aldehydes. The present results eliminate a possible mechanism for this isomerization wherein cyclopropane derivatives occur as intermediates.