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1.
Biosynthetic pathways to p-hydroxybenzoic acid in polar lignin were examined by tracer experiments. High incorporation of radioactivity to the acid was observed when shikimic acid-[1-14C], phenylalanine-[3-14C], trans-cinnamic acid-[3-14C], p-coumaric acid-[3-14C] and p-hydroxybenzoic acid-[COOH-14C] were administered, while incorporation was low from shikimic acid-[COOH-14C], phenylalanine-[1-14C], phenylalanine-[2-14C], tyrosine-[3-14C], benzoic acid-[COOH-14C], sodium acetate-[1-14C] and d-glucose-[U-14C]. Thus p-hydroxybenzoic acid in poplar lignin is formed mainly via the pathway: shikimic acid → phenylalanine → trans-cinnamic acid → p-coumaric acid → p-hydroxybenzoic acid. 相似文献
2.
Tracer feeding experiments with Camptotheca acuminata plants show that [1′-14C]L-tryptophan, [Ar-3H4]L-tryptophan, [Ar-3H4,1′-14C]tryptophan, [1′-14C]-tryptamine, [2-14C]DL-mevalonate, and [2-14C]geraniol-[2-14C]nerol are incorporated into camptothecin. Direct stem injection of the labeled precursors into C. acuminata plants resulted in a substantial increase in the activity of isolated Camptotheca alkaloids as compared to root feeding of the same tracer. 相似文献
3.
In Vivo Pathway of Oleate and Linoleate Desaturation in Developing Cotyledons of Cucumis sativus L. Seedlings 总被引:6,自引:5,他引:1
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Exogenous [1-14C]oleic acid and [1-14C]linoleic acid were taken up and esterified to complex lipids by greening cucumber (Cucumis sativus L.) cotyledons. Both 14C-labeled fatty acids were initially esterified to phosphatidylcholine prior to eventual accumulation in triacylglycerols and galactolipids. Kinetic data suggest that esterification occurs prior to desaturation and that phosphatidylcholine is the initial site of both [14C]-oleate and [1-14C]linoleate esterification and of [1-14C]oleate desaturation to [1-14C]linoleate. [1-14C]Linoleic acid was esterified more rapidly than [14C]oleic acid and its desaturation product, [1-14C]α-linolenate, occurred mainly on monogalactosyl diacylglycerol, although some was also observed on the other major acyl lipids, including phosphatidylcholine. 相似文献
4.
Sodium [1-14C]acetate, sodium [1-14C]propionate, sodium [2-14C]propionate, sodium [3-14C]propionate and sodium [methyl-14C]methylmalonate were readily incorporated into the cuticular hydrocarbons of nymphal stages of the cockroach Periplaneta fuliginosa both in vivo and in vitro, whereas no incorporation of [methyl-14C]methionine was observed. The alkanes of the nymphal stages of this insect are 25+% n-alkanes, 14% 3-methylalkanes, and 59+% internally branched monomethylalkanes, principally 13-methylpentacosane. Sodium [1-14C]acetate was incorporated into each class of alkane at about its percentage composition. In contrast, labeled sodium propionate and sodium methylmalonate were preferentially incorporated into the branched fractions. Radio-gas-liquid chromatography showed that sodium [1-14C]propionate was incorporated almost exclusively into 3-methyltricosane and 13-methylpentacosane, whereas sodium [1-14C]acetate was incorporated into each glc peak at about its percentage composition. These data suggest that propionate, incorporated during chain elongation, serves as the branching methyl group donor for both the 3-methyl and the internally branched monomethylalkanes in insects. The location of hydrocarbon synthesis in P. fuliginosa was studied using an in vitro tissue slice system. Excised cuticle slices, with adhering fat body tissue removed, gave good incorporation of labeled substrates into the hydrocarbon fraction. No hydrocarbon synthesis was observed in fat body preparations. 相似文献
5.
Kjetil Retterstøl Trine B. Haugen Bjørn O. Christophersen 《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》2000,1483(1):119-131
The concentration-dependent metabolism of 1-14C-labelled precursors of 22:5n-6 and 22:6n-3 was compared in rat testis cells. The amounts of [14C]22- and 24-carbon metabolites were measured by HPLC. The conversion of [1-14C]20:5n-3 to [3-14C]22:6n-3 was more efficient than that of [1-14C]20:4n-6 to [3-14C]22:5n-6. At low substrate concentration (4 μM) it was 3.4 times more efficient, reduced to 2.3 times at high substrate concentration (40 μM). The conversion of [1-14C]22:5n-3 to [1-14C]22:6n-3 was 1.7 times more efficient than that of [1-14C]22:4n-6 to [1-14C]22:5n-6 using a low, but almost equally efficient using a high substrate concentration. When unlabelled 20:5n-3 was added to a cell suspension incubated with [1-14C]20:4n-6 or unlabelled 22:5n-3 to a cell suspension incubated with [1-14C]22:4n-6, the unlabelled n-3 fatty acids strongly inhibited the conversion of [1-14C]20:4n-6 or [1-14C]22:4n-6 to [14C]22:5n-6. In the reciprocal experiment, unlabelled 20:4n-6 and 22:4n-6 only weakly inhibited the conversion of [1-14C]20:5n-3 and [1-14C]22:5n-3 to [14C]22:6n-3. The results indicate that if both n-6 and n-3 fatty acids are present, the n-3 fatty acids are preferred over the n-6 fatty acids in the elongation from 20- to 22- and from 22- to 24-carbon atom fatty acids. In vivo the demand for 22-carbon fatty acids for spermatogenesis in the rat may exceed the supply of n-3 precursors and thus facilitate the formation of 22:5n-6 from the more abundant n-6 precursors. 相似文献
6.
The biosynthesis of the morphinandienone alkaloids norsinoacutine, sinoacutine and flavinantine has been studied using 1-3 H-sinoacutine, 1-3H-norsinoacutine, 1-3H-norsinoacutinols, l-[S-methyl-14C]-methionine, glycine-2-14C, 1-3H-8,14-dihydronorsalutaridine, 1-3 H-8,14-dihydrosalutaridine, 1-3H-sinomenine, 1-3H-isosinomenine, (±)-[2-14C]phenylalanine, (±)-[N-methyl-14C]orientaline and (±)-[N-methyl-14C]reticuline. 相似文献
7.
Microbial reductive dechlorination of [1,2-14C]trichloroethene to [14C]cis-dichloroethene and [14C]vinyl chloride was observed at 4°C in anoxic microcosms prepared with cold temperature-adapted aquifer and river sediments from Alaska. Microbial anaerobic oxidation of [1,2-14C]cis-dichloroethene and [1,2-14C]vinyl chloride to 14CO2 also was observed under these conditions. 相似文献
8.
Schistosoma mansoni: glycosyl transferase activity and the carbohydrate composition of the tegument.
Homogenates of adult Schistosoma mansoni contain enzymes which transferred [14C]mannose, [14C]glucose, and [14C]galactose from GDP-[U-14C]mannose, UDP-[U-14C]glucose, and UDP-[U-14C]galactose respectively to a lipid acceptor; in comparison, free [14C]mannose, GDP-[U-14C]fucose, and UDP-[U-14C]acetyl-glucosamine were poorly transferred. The lipid acceptor is believed to be an intermediate in the glycosylation of the worm's glycoproteins and in the biosynthesis of oligosaccharides and glycolipids. The tegument of adult worms was isolated by the freeze-thaw procedure and sugars associated with macromolecules in this fraction were analyzed; the major monosaccharide components were glucose, galactose, and mannose. These results suggest that the mechanism of glycosylation of the adult schistosome's tegumental macromolecules may occur through the glycosyl transferase system. The schistosome mannosyl transferase (EC 2.4.1), which is membrane bound was solubilized with 0.1% Triton X-100 without loss of activity; after density gradient centrifugation there was a peak of enzymic activity in a region of density 1.08, which could not be associated with any particular organelle. 相似文献
9.
Edward Bellion David H. Kirkley Jerry R. Faust 《Biochimica et Biophysica Acta (BBA)/General Subjects》1976,437(1):229-237
The mechanism of biosynthesis of 4-methyl-5-β-hydroxyethyl thiazole, the thiazole moiety of thiamine was studied in Salmonella typhimurium. Using the adenosine derepression technique the incorporation of various 14C-labeled precursors was determined. We found that [Me-14C]methionine, [2-14C]methionine, [U-14C]alanine, and [2-14C]glycine were not incorporated whereas [2-14C]-tyrosine was incorporated. Degradation of the 4-methyl-5-β-hydroxyethyl thiazole obtained after [2-14C]tyrosine incorporation revealed that all of the activity was located on carbon-2. These findings are discussed and compared with previous findings concerning 4-methyl-5-β-hydroxyethyl thiazole biosynthesis. 相似文献
10.
《Insect Biochemistry》1986,16(1):17-23
The synthesis of [4-14C]cholesta-4,6-dien-3-one and [4-14C]3β-hydroxy-5α-cholestan-6-one is described. Both [4-14C]cholest-4-en-3-one and [4-14C]cholesta-4,6-dien-3-one were not incorporated significantly into ecdysteroids compared to [1α,2α-3H]cholesterol in fifth instar and maturing adult female Schistocerca gregaria. Similarly, [4-14C]3β-hydroxy-5α-cholestan-6-one was not incorporated significantly in the latter system. The results suggest that none of the three 14C-substrates are intermediates in ecdysteroid biosynthesis from cholesterol, although possible complications from permeability barriers cannot be discounted. [4-14C, 7-3H]7-dehydrocholesterol has been synthesized and incorporated into ecdysteroids in adult female Schistocerca gregaria and in Spodoptera littoralis pupae. Although approximately half the tritium was eliminated during ecdysteroid synthesis in S. gregaria, there was essentially complete retention of the tritium in Spodoptera. The results support the direct incorporation of 7-dehydrocholesterol into ecdysteroids and not via cholesterol. A possible explanation for the loss of appreciable tritium in S. gregaria is discussed. 相似文献
11.
A quantitative triterpene analysis was made of latex stem tissue of Euphorbia lathyris. Young plants seedlings of E. lathyris were incubated with various labelled precursors. Incorporation into triterpenes was obtained from [2-14C]mevalonic acid, [1-14C]acetate, [3-14C]pyruvate, [U-14C]sucrose, [U-14C]glucose, [U-14C]xylose, [U-14C]glyoxylate, [2,3-14C]succinic acid, [1-14C]glycerol [U-14C]serine. Both sugars tyrosine appeared to be effective precursors in DOPA synthesis inside the laticifers. Exogenously supplied mevalonic acid was only involved in triterpene synthesis outside the laticifers. GC-RC of triterpenes synthesized from [U-14C]glucose revealed the origin of these compounds in the latex. The labelled triterpenes obtained after incorporation of the other mentioned labelled precursors were only partly synthesized in the laticifers. For quantitative data on latex triterpene synthesis seedlings were incubated with [U-14C]sucrose, [U-14C]glucose, [U-14C]xylose [1-14C]acetate in the presence of increasing amounts of unlabelled substrate. From the amount of 14C incorporated into the triterpenes the amount of substrate directly involved in triterpene synthesis was calculated, as was the absolute triterpene yield. Sucrose showed the highest triterpene yield, equivalent to the daily increase of the triterpene content of growing seedlings. The possible significance of the other precursors in triterpene synthesis in the laticifers is discussed. 相似文献
12.
Paul M. Dewick 《Phytochemistry》1975,14(4):983-988
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
13.
A simple, three-step conversion of 1,2-O-isopropylidene-α-d-glucofuranose into l-ascorbic acid, originally described by Bakke and Theander, was used to prepare l-[4-14C]ascorbic acid from milligram amounts of d-[3-14C]glucopyranose in 28% radioisotopic yield. In addition, l-[6-14C]- and l-[U-14C]-ascorbic acid were prepared from d-[1-14C]- and d-[U-14C]-glucopyranose, respectively. The procedure is useful for the synthesis of l-ascorbic acid bearing isotopic hydrogen, carbon, or oxygen atoms at specific positions, subject only to the availability of starting material. 相似文献
14.
The metabolism of D-[1-14C]glucose, D-[6-14C]glucose, D-[1-14C]fructose and D-[6-14C]fructose by leafy spurs of Itea plants results in rapid incorporation of label into allitol and D-allulose. The patterns of labelling found in the allitol and D-allulose are discussed, a direct interconversion from D-glucose and D-fructose being indicated. Allitol has been found to be an active metabolite in Itea plants. 相似文献
15.
Saito K 《Plant physiology》1978,62(2):215-219
[U-14C]Sucrose, myo-[U-14C]inositol, [6-14C]- and [U-14C]glucuronate, UDP-[U-14C]glucuronate, [U-14C]gluconate, and l-[1-14C]ascorbic acid were fed into grape berries, Vitis labrusca L. cv. Delaware, at intervals throughout the ripening process and incorporation of 14C into several metabolites was studied. 相似文献
16.
The metabolism of d-gluconate-[1-14C] and -[6-14C] by segments from etiolated hypocotyls of Phaseolus mungo has been studied. The release of 14CO2 from gluconate-[1-14C] was greater than that from gluconate-[6-14C] in all parts of hypocotyls examined. Incorporation of the radioactivity from gluconate-[6-14C] into RNA, lignin and aromatic amino acid fractions was greater in the upper (younger) part of the hypocotyls. Incorporation into sugars was greater in the lower (more mature) parts. 相似文献
17.
P.M. Dewick 《Phytochemistry》1978,17(2):249-250
dl-Phenylalanine-[2-14C], 2′,4′,4-trihydroxychalcone-[carbonyl-14C] and formononetin-[Me-14C] were all good precursors of afrormosin (7-hydroxy-6,4′-dimethoxyisoflavone) in Onobrychis viciifolia seedlings. This demonstrates that 6-oxygenation may be a late process in the biosynthesis of isoflavones. 相似文献
18.
Time-course tracer studies were performed on the metabolism of trans-cinnamic acid-[3-14C] and trans-p-coumaric acid-[2-14C] in the 相似文献
19.
Convallaria majalis plants were fed dl-methionine-[1-14C]. [1-14C, 4-3H], and [1-14C, 2-3H], S-adenosyl-l-methionine-[1-14C], and dl-homoserine-[1-14C], resulting in the formation of labeled azetidine-2-carboxylic acid (A-2-C). The complete retention of tritium relative to carbon-14 in the feeding experiment involving methionine-[1-14C, 4-3H] indicates that aspartic acid or aspartic-β-semialdehyde are not intermediates between methionine and A-2-C. However, since the A-2-C derived from methionine-[1-14C, 2-3H] had lost 95% of the tritium relative to the C-14, it is not considered that methionine or its S-adenosyl derivative are the immediate precursors of A-2-C. Our data and that of others is consistent with the intermediate formation of γ-amino-α-ketobutyric acid which on cyclization yields 1-azetine-2-carboxylic acid, A-2-C then being formed on reduction. 相似文献
20.
[1-14C]Octadecyl glyceryl ether did not label alkanes in the leaves of Brassica oleracea and Pisum sativum while [1-14C]octadecanol and [1-14C]octadecanoic acid readily labeled the alkanes. About 40% of the exogenous-labeled glyceryl ether was incorporated intact into choline phosphatide while 10–20% was converted into fatty acids and alcohols. [1-14C]octadecanol was not converted into alkyl glyceryl ether, but it was oxidized to the corresponding acid and then incorporated into alkanes. These results show that alkyl ether is not an intermediate in alkane biosynthesis. When [1-14C-1-3H]-octadecanol was fed to the leaves of B. oleracea and P. sativum, only the 14C and no 3H was incorporated into alkanes, ketones, and secondary alcohols. These results show that fatty alcohols are first oxidized to the acid before being incorporated into alkanes, ruling out fatty alcohol, alkyl ether, and alk-1-enyl ether as intermediates in alkane biosynthesis. The exogenous alcohols were also readily esterified into wax esters in both tissues. 相似文献