首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
The in vitro cultured liverwort Jungermannia subulata produces the unique molecule subulatin. In this study, we examined the incorporation of [1-13C] and [1,2-13C2] glucose, [2-13C] arabinose, [2-13C] caffeic acid, and [1-13C] phenylalanine into subulatin. The trilobatinoic acid C unit of subulatin incorporated 13C atoms from [1-13C] and [1,2-13C2] glucose and from [2-13C] arabinose but not from any other of the other precursors. Based on these results and labeling patterns, the trilobatinoic acid C unit of subulatin appears to be biosynthesized from arabinose-5-phosphate and phosphoenolpyruvate.  相似文献   

2.
An incorporation study of [1-13C] and [1,2-13C2] labeled sodium acetates into sorbicillinol 1 established a ring closure system between C-1 and C-6 and the positions that were oxidized and/or methylated on a hexaketide chain. Subsequent investigations, using 13C-labeled 1 prepared from [1-13C] labeled sodium acetate, clearly demonstrated that both bisorbicillinol 2 and sorbicillin 6 incorporated 13C-labeled 1 into their carbon skeletons. 13C-labeled bisorbicillinols 2 derived from [1-13C]- and [2-13C]-labeled sodium acetates clearly indicate that these were on the biosynthetic route from 1 to bisorbibutenolide (bislongiquinolide) 3 and bisorbicillinolide 4 via 2 as a branching point in the fungus.  相似文献   

3.
Feeding of benzoic acid-[7-14C], benzaldehyde-[7-14C] and cinnamic acid-[3-14C] to Ephedra distachya resulted in efficient incorporations of 14C into the α-carbon atom of the side chain of l-ephedrine. Thus ephedrine was shown to be biosynthesized by the condensation of a C6C1 portion which is derived from phenylalanine via cinnamate and an unidentified C2-N fragment.  相似文献   

4.
The biosynthesis of fukinolic acid, which had been isolated from the Japanese fuki vegetable, Petasites japonicus, was investigated by feeding selected 13C-labeled compounds to axenic cultures of P. japonicus. [1,2-13C2] sodium acetate and [1-13C] L-tyrosine were incorporated into the fukiic acid sub group, while [3-13C] L-phenylalanine was incorporated into the caffeic acid moiety.  相似文献   

5.
Artemisinin is a well-known antimalarial drug isolated from the Artemisia annua plant. The biosynthesis of this well-known molecule has been reinvestigated by using [1-13C]acetate, [2-13C]acetate, and [1,6-13C2]glucose. The 13C peak enrichment in artemisinin was observed in six and nine carbon atoms from [1-13C]acetate and [2-13C]acetate, respectively. The 13C NMR spectra of 13C-enriched artemisinin suggested that the mevalonic acid (MVA) pathway is the predominant route to biosynthesis of this sesquiterpene. On the other hand, the peak enrichment of five carbons of 13C-artemisinin including carbon atoms originating from methyls of dimethylallyl group of geranyl pyrophosphate (GPP) and farnesyl pyrophosphate (FPP) was observed from [1,6-13C2]glucose. This suggested that GPP which is supposed to be biosynthesized in plastids travels from plastids to cytosol through the plastidial wall and combines with isopentenyl pyrophosphate (IPP) to form the (E,E)-FPP which finally cyclizes and oxidizes to artemisinin. In this way the DXP pathway also contributes to the biosynthesis of this sesquiterpene.  相似文献   

6.
Long chain fatty acid synthesis was studied using etiolated leek seedling microsomes. In the presence of ATP, [2-14C]malonyl-CoA was incorporated into fatty acids of C16C26. The omission of ATP, even in the presence of acetyl-CoA, led to a complete loss of activity, which was restored by addition of exogeneous acyl-CoAs. Comparison of acyl-CoA (C12C24) elongation showed that stearoyl-CoA, in the presence of [2-14C]malonyl-CoA, was the more efficient precursor leading to the formation of fatty acids having a chain length of C20C26. [1-14C]C16CoA and [1-14C]C18CoA were elongated in the presence of malonyl-CoA, without degradation of the acyl chain. The time-course and the malonyl-CoA concentration curves showed that [1-14C]C18CoA was a better primer than [1-14C]C16CoA. Acyl-CoA elongation was also studied over the concentration range 4.5–45 μM [1-14C]C18CoA. Comparison of the radioactivity incorporated into the fatty acids formed using [2-14C]malonyl-CoA in the presence of C18CoA, on the one hand, and [1-14C]C18CoA in the presence of malonyl-CoA, on the other, demonstrated clearly that the acyl chain of the acyl-CoA was elongated by malonyl-CoA.  相似文献   

7.
《Insect Biochemistry》1990,20(2):149-156
The precursors and directionality of synthesis of the methyl branched cuticular hydrocarbons and the female contact sex pheromone, 3,11-dimethyl-2-nonacosanone, of the German cockroach, Blattella germanica, were investigated by radiotracer and carbon-13 NMR techniques. The amino acids [G-3H]valine, [4,5-3H]isoleucine and [3,4-14C2]methionine labeled the hydrocarbon fraction in a manner indicating that the carbon skeletons of all three amino acids serve as the methyl branch group donor. The incorporation of [1,4-14C2]- and [2,3-14C2]succinates into the hydrocarbon and acylglycerol/polar lipid fractions indicated that succinate also served as a precursor to methylmalonyl-CoA. Carbon-13 NMR analyses showed that [1-13C]propionate labeled the carbon adjacent to the tertiary carbon, and, for the 3,x-dimethylalkanes, that carbon-4 and not carbon-2 was enriched. [1-13C]Acetate labeled carbon-2 of these hydrocarbons. This indicates that the methyl branching groups of the 3,x-dimethylalkanes were inserted early in the chain elongation process. [3,4,5-13C3]Valine labeled the methyl, tertiary and carbon adjacent to the tertiary carbon of the methyl branched alkanes. Thus, the methyl branched hydrocarbon was formed by the insertion of methylmalonyl units derived from propionate, isoleucine, valine, methionine and succinate early in chain elongation.  相似文献   

8.
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.  相似文献   

9.
Feeding experiments have demonstrated the specific incorporation of radioactivity from dl-phenylalanine-[1-14C], l-phenylalanine-[U-14C], sodium acetate-[2-14C] and l-methionine-[methyl-14C] into the 3-benzylchroman-4-one eucomin in Eucomis bicolor. The labelling patterns indicate that eucomin is biosynthesized by the addition of a carbon atom derived from methionine onto a C15 chalcone-type skeleton. Radioactivity from 2′,4′,4-trihydroxy-6′-methoxychalcone-[methyl-14C] and 2′,4′-dihydroxy-4,6′-dimethoxychalcone-[6′-methyl-14C] was incorporated into eucomin, the latter compound being the better precursor, demonstrating the feasibility that 2′-methoxychalcones are biosynthetic precursors of the “homoisoflavonoids”. Possible biosynthetic relationships in this class of compounds are discussed.  相似文献   

10.
Summary [2-13C]-L-lysine, [3,4-13C2]-L-lysine and [5,6-13C2]-L-lysine are prepared from simple, commercially available, highly enriched starting materials as [2-13C]-glycine, ethyl [1,2-13C2]-bromo acetate, and [1,2-13C2]-acetonitrile. The introduction of the chiral center is based on a general method starting from the bis-lactim ether of cyclo-(D-Val-Gly). The synthesis of (2R)-[5-13C]-3,6-diethoxy-2,5-dihydro-2-isopropylpyrazine is described. The availability of our method for the preparation of specifically enriched bis-lactim ethers allows the synthesis of a great variety of site specific isotopically labelled (L- and D-)-amino acids. Moreover, intermediate 4-[(2R,5S)-3,6-diethoxy-2,5-dihydro-2-isopropyl-5-pyrazinyl]butyronitrile is a valuable precursor in the synthesis of L--aminoadipic acid. The synthetic scheme in this publication makes both L-lysine and L--aminoadipic acid13C- or15N-labelled at any position, easily available. The isotopomers of lysine are obtained on a preparative scale in good yields, with 99%13C and high enantiomeric purity (>97% e.e.). Three isotopomers are characterized using various spectroscopic techniques,e.g.,1H NMR,13C NMR and Mass spectrometry.  相似文献   

11.
Isolated hepatocytes from fed rats were exposed for 120 min to D-glucose (10 mM) and either D-[1-13C]fructose, D-[2-13C]fructose or D-[6-13C]fructose (also 10 mM) in the presence of D2O. The identification and quantification of 13C-enriched D-fructose and its metabolites (D-glucose, L-lactate, L-alanine) in the incubation medium and the measurement of their deuterated isotopomers indicated, by comparison with a prior study conducted in the absence of exogenous D-glucose, that the major effects of the aldohexose were to increase the recovery of 13C-enriched D-fructose, decrease the production of 13C-enriched D-glucose, restrict the deuteration of the 13C-enriched isotopomers of D-glucose to those generated by cells exposed to D-[2-13C]fructose, and to accentuate the lesser deuteration of the C2 (as compared to C5) of 13C-enriched D-glucose derived from D-[2-13C]fructose. The ratio between C2-deuterated and C2-hydrogenated L-lactate, as well as the relative amounts of the CH3-, CH2D-, CHD2 and CD3- isotopomers of 13C-enriched L-lactate were not significantly different, however, in the absence or presence of exogenous D-glucose. These findings indicate that exogenous D-glucose suppressed the deuteration of the C1 of D-[1-13C]glucose generated by hepatocytes exposed to D-[1-13C]fructose or D-[6-13C]fructose, as otherwise attributable, in part at least, to gluconeogenesis from fructose-derived [3-13C]pyruvate, and apparently favoured the phosphorylation of D-fructose by hexokinase isoenzymes, probably through stimulation of D-fructose phosphorylation by glucokinase.  相似文献   

12.
The structure of a new ten-membered lactone, achaetolide, isolated from cultures of Achaetomium cristalliferum is deduced from its mass and NMR spectra and from the study ofsomederivatives. The 13C NMR spectra of achaetolide enriched with [1-13C], [2-13C] and [1, 2-13C] acetate established its formation from eight intact acetate units via a precursor octaketide chain.  相似文献   

13.
Summary The discrimination between the isotopes of hydrogen in the reaction catalyzed by yeast phosphoglucoisomerase is examined by NMR, as well as by spectrofluorometric or radioisotopic methods. The monodirectional conversion of D-glucose 6-phosphate to D-fructose 6-phosphate displays a lower maximal velocity with D-[2-2H]glucose 6-phosphate than unlabelled D-glucose 6-phosphate, with little difference in the affinity of the enzyme for these two substrates. About 72% of the deuterium located on the C2 of D-[1-13C,2-2H]glucose 6-phosphate is transferred intramolecularly to the C1 of D-[1-13C,1-2H]fructose 6-phosphate. The velocity of the monodirectional conversion of D-[U-14C]glucose 6-phosphate (or D-[2-3H]glucose 6-phosphate) to D-fructose 6-phosphate is virtually identical in H2O and D2O, respectively, but is four times lower with the tritiated than 14C-labelled ester. In the monodirectional reaction, the intramolecular transfer from the C2 of D-[2-3H]glucose 6-phosphate is higher in the presence of D2O than H2O. Whereas prolonged exposure of D-[1-13C]glucose 6-phosphate to D2O, in the presence of phosphoglucoisomerase, leads to the formation of both D-[1-13C,2-2H]glucose 6-phosphate and D-[1-13C,1-2H]fructose 6-phosphate, no sizeable incorporation of deuterium from D2O on the C1 of D-[1-13C]fructose 1,6-bisphosphate is observed when the monodirectional conversion of D-[1-13C]glucose 6-phosphate occurs in the concomitant presence of phosphoglucoisomerase and phosphofructokinase. The latter finding contrasts with the incorporation of hydrogen from 1H2O or tritium from 3H2O in the monodirectional conversion of D-[2-3H]glucose 6-phosphate and unlabelled D-glucose 6-phosphate, respectively, to their corresponding ketohexose esters.  相似文献   

14.
The objective of this study was to elucidate the biosynthetic route to 4-methyl-1-nonanol, the female-produced sex pheromone of the yellow mealworm beetle, Tenebrio molitor L. The biosynthetic route to the pheromone was examined by (i) allowing the females to feed on defatted bran coated with a stable isotope-labeled putative precursor ([1-13C]acetate, [1-13C]propionate, [1-13C]pentanoate, [1-13C]2-methylheptanoic acid, or [2H2]4-methylnonanoic acid); (ii) determining if the precursors were incorporated by analyzing the emitted pheromone by gas chromatography/selected ion monitoring-mass spectroscopy (GC/SIM-MS); (iii) where the pheromone was isotopically-enriched, determining the position of the isotopic label(s) through comparison of the MS fragmentation pattern with that of unlabelled 4-methyl-1-nonanol. Although the incorporation of [1-13C]acetate into 4-methyl-1-nonanol could not be detected, relatively large proportions of the pheromone were produced from the other precursors tested: 81% from [2H2]4-methylnonanoic acid, 45% from [1-13C]2-methylheptanoic acid, 16% from [1-13C]pentanoate, and 35% from [1-13C]propionate (27% from only one unit, and 7.8% from two units). The results indicate that 4-methyl-1-nonanol is produced through a modification of normal fatty acid biosynthesis: initiation of the pathway with one unit of propionate results in the uneven number of carbons in the chain; incorporation of another unit of propionate during elongation provides the methyl branch; reduction of 4-methylnonanoic acid produces the alcohol pheromone. The elucidation of the biosynthetic pathway of 4-methyl-1-nonanol biosynthesis in the yellow mealworm is the first step towards understanding the biochemistry of sex pheromone production in this species.  相似文献   

15.
The 13C-nuclear magnetic resonance (NMR) spectra of chlorophyll a formed in dark-grown Scenedesmus obliquus (Turp.) Kützing in the presence of [1-13C]glutamate, [2-13C]- and [1-13C]glycineshowed that the 13C of glutamate was specifically incorporated into the eight-carbon atoms in the tetrapyrrole macrocycles derived from C-5 of 5-aminolevulinic acid (ALA), while the C-2 of glycine was only incorporated into the methyl carbon of the methoxycarbonyl group attached to the isocyclic ring of chlorophyll a. No specific enrichment of these nine carbon atoms was observed in the spectrum of chlorophyll a formed in the presence of [1-13C]-glycine. These labeling patterns provide evidence for the operation of the C5-pathway and against the operation of the ALA synthase pathway for chlorophyll formation in darkness.  相似文献   

16.
Summary The exchange of protons and deuterons by phosphoglucoisomerase during the single passage conversion of D-[2-13C,1-2H]fructose 6-phosphate in H2O or D-[2-13C]fructose 6-phosphate in D2O to D-[2-13C]glucose 6-phosphate, as coupled with the further generation of 6-phospho-D-[2-13C]gluconate in the presence of excess glucose-6-phosphate dehydrogenase was investigated by 13C NMR spectroscopy of the latter metabolite. In H2O, the intramolecular deuteron transfer from the C1 of D-fructose 6-phosphate to the C2 of D-glucose 6-phosphate amounted to 65%, a value only slightly lower than the 72% intramolecular proton transfer in D2O. Both percentages, especially the latter one, were lower than those previously recorded during the single passage conversion of D-[1-13C,2-2H]glucose 6-phosphate in H2O or D-[1-13C]glucose 6-phosphate in D2O to D-fructose 6-phosphate and then to D-fructose 1,6-bisphosphate. These differences indicate that the sequence of interactions between the hexose esters and the binding sites of phosphoglucoisomerase is not strictly in mirror image during, respectively, the conversion of the aldose phosphate to ketose phosphate and the opposite process.  相似文献   

17.
After exposure to [U-13C3]glycerol, the liver produces primarily [1,2,3-13C3]- and [4,5,6-13C3]glucose in equal proportions through gluconeogenesis from the level of trioses. Other 13C-labeling patterns occur as a consequence of alternative pathways for glucose production. The pentose phosphate pathway (PPP), metabolism in the citric acid cycle, incomplete equilibration by triose phosphate isomerase, or the transaldolase reaction all interact to produce complex 13C-labeling patterns in exported glucose. Here, we investigated 13C labeling in plasma glucose in rats given [U-13C3]glycerol under various nutritional conditions. Blood was drawn at multiple time points to extract glucose for NMR analysis. Because the transaldolase reaction and incomplete equilibrium by triose phosphate isomerase cannot break a 13C-13C bond within the trioses contributing to glucose, the appearance of [1,2-13C2]-, [2,3-13C2]-, [5,6-13C2]-, and [4,5-13C2]glucose provides direct evidence for metabolism of glycerol in the citric acid cycle or the PPP but not an influence of either triose phosphate isomerase or the transaldolase reaction. In all animals, [1,2-13C2]glucose/[2,3-13C2]glucose was significantly greater than [5,6-13C2]glucose/[4,5-13C2]glucose, a relationship that can only arise from gluconeogenesis followed by passage of substrates through the PPP. In summary, the hepatic PPP in vivo can be detected by 13C distribution in blood glucose after [U-13C3]glycerol administration.  相似文献   

18.
Lens PN  Dijkema C  Stams AJ 《Biodegradation》1998,9(3-4):179-186
Applications of nuclear magnetic resonance (NMR) to study a variety of physiological and biochemical aspects of bacteria with a role in the sulfur cycle are reviewed. Then, a case-study of high resolution13 C-NMR spectroscopy on sludges from bioreactors used for treating sulfate and sulfide rich wastewaters is presented.13 C-NMR was used to study the effect of sulfate and butyrate on propionate conversion by mesophilic anaerobic (methanogenic and sulfate reducing) granular sludge and microaerobic (sulfide oxidizing) flocculant sludge. In the presence of sulfate, propionate was degraded via the randomising pathway in all sludge types investigated. This was evidenced by scrambling of [3-13C]propionate into [2-13C]propionate and the formation of acetate equally labeled in the C1 and C2 position. In the absence of sulfate, [3-13C]propionate scrambled to a lesser extend without being degraded further. Anaerobic sludges converted [2,3-13C]propionate partly into the higher fatty acid 2-methyl[2,3-13C]butyrate during the simultaneous degradation of [2,3-13C]propionate and butyrate. [4,5-13C]valerate was also formed in the methanogenic sludges. Up to 10% of the propionate present was converted via these alternative degradation routes. Labeled butyrate was not detected in the incubations, suggesting that reductive carboxylation of propionate does not occur in the sludges.  相似文献   

19.
We present a 13C direct detection CACA-TOCSY experiment for samples with alternate 13C–12C labeling. It provides inter-residue correlations between 13Cα resonances of residue i and adjacent Cαs at positions i − 1 and i + 1. Furthermore, longer mixing times yield correlations to Cα nuclei separated by more than one residue. The experiment also provides Cα-to-sidechain correlations, some amino acid type identifications and estimates for ψ dihedral angles. The power of the experiment derives from the alternate 13C–12C labeling with [1,3-13C] glycerol or [2-13C] glycerol, which allows utilizing the small scalar 3JCC couplings that are masked by strong 1JCC couplings in uniformly 13C labeled samples.  相似文献   

20.
A capillary gas chromatographic—mass spectrometric method for the simultaneous determination of stable isotopically labelled l-histidine (l-[3,3-2H2,1′,3′-15N2]histidine, l-His-[M + 4]) and urocanic acid ([3-2H,1′,3′-15N2]urocanic acid, UA-[M + 3]) in human plasma was developed using dl-[2,3,3,5′-2H4,2′-13C,1′,3′-15N2]histidine (dl-His-[M + 7]) and [2,3,5′-2H3,2′-13C,1′,3′-15N2]urocanic acid (UA-[M + 6]) as internal standards. l-Histidine and urocanic acid were derivatized to αN-(trifluoroacetyl)-imN-(ethoxycarbonyl)-l-histidine n-butyl ester and imN-(ethoxycarbonyl)urocanic acid n-butyl ester. Quantification was carried out by selected ion monitoring of the molecular ions of the respective derivatives of l-His-[M + 4], dl-His-[M + 7], UA-[M + 3] and UA-[M + 6]. The sensitivity, specificity, precision and accuracy of the method were demonstrated to be satisfactory for measuring plasma concentrations of l-His-[M + 4] and UA-[M + 3] following administration of trace amounts of l-His-[M + 4] to humans.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号