共查询到20条相似文献,搜索用时 15 毫秒
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Chlorophyll and nitrogen contents were highest in leaves of middle position, similarly as photosynthetic efficiency represented by 14C fixation (maxima in leaf 5 from the top). All the leaves lost 14C after 2 weeks of 14CO2 exposure. However, the reduction in radioactivity was less in young upper leaves than in the mature lower leaves. Leaves exported 14C-photosynthates to stem both above and below the exposed leaf. Very little radioactivity was recovered from the seeds of plants in which only first or second leaves were exposed to 14CO2 implying thereby that the carbon contribution of first two leaves to seed filling was negligible. The contribution of leaves to seed filling increased with the leaf position up to the sixth leaf from the top and after the seventh leaf their contribution to seed filling declined gradually. 相似文献
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2-Carboxyarabinitol 1-phosphate (CAIP) is involved in the regulationof ribulose 1,5-bisphosphate carboxylase (rubisco) activityin many plants, but the biochemical pathway for its synthesisis unknown. In an attempt to induce synthesis of 14C-CAIP invivo, intact leaflets of Phaseolus vulgaris were pulse-labeledwith 14CO2 and chased with 12CO2 under conditions which resultin leaves accumulating unlabeled CAIP. Sugar-phosphates wereisolated from leaf extracts by anion exchange chromatographyand constituent metabolites were separated by 2D-thin-layerchromatography. No l4C-labeled CAIP was recovered from extractsprepared from leaves experiencing a range of exposure/chaseconditions, a range of leaf/plant ages, or from other speciesdiffering in their ability to accumulate unlabeled CAIP. Appropriatecontrol experiments indicated no loss of 14C-standard whichhad been added at the time of killing the leaf. The data suggestthat carboxyarabinitol 1-phosphate is not synthesized in vivoas some "misfire" catalysis by rubisco, and that the precursorto its synthesis is far "downstream" of CO2 fixation. (Received May 11, 1990; Accepted July 19, 1990) 相似文献
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The incorporation of 14CO2 by an exponentially growing culture of the autotrophic bacterium Methanobacterium thermoautotrophicum has been studied. The distribution of radioactivity during 2s–120s incubation periods has been analyzed by chromatography and radioautography. After a 2 s incubation most of the radioactivity of the ethanolsoluble fraction was present in the amino acids alanine, glutamate, glutamine and aspartate, whereas phosphorylated compounds were only weakly labelled. The percentage of the total radioactivity fixed, which was contained in the principal early labelled amino acid alanine, increased in the first 20 s and only then decreased, indicating that alanine is derived from primary products of CO2 fixation.The labelling patterns of alanine produced during various incubation times have been determined by degradation. After a 2 s 14CO2 pulse, 61% of the radioactivity was located in C-1, 23% in C-2, and 16% in C-3. The results are consistent with the operation of a previously proposed autotrophic CO2 assimilation pathway which involves the formation of acetyl CoA from 2 CO2 via one-carbon unit intermediates, followed by the reductive carboxylation of acetyl CoA to pyruvate. 相似文献
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C F Howard 《Journal of lipid research》1971,12(6):725-730
Lipogenesis was measured with glucose-2-(14)C and acetate-1-(14)C in the everted aortas of normal and atherosclerotic rabbits. More glucose-2-(14)C than acetate-1-(14)C was incorporated into lipids in both the normal and the atherosclerotic aorta. Radiocarbon from glucose-2-(14)C appeared mainly in triglycerides and phospholipids with a small amount in cholesteryl esters. Incorporation increased almost threefold with atherosclerosis, most of the radioactivity being in the glycerol moiety; radioactivity was predominantly in carbon 2 of glycerol. About 70% of the acetate-1-(14)C incorporated into phospholipids and triglycerides was in the fatty acids, and the remainder was in glyceride-glycerol; 98% of the radioactivity in cholesteryl esters was in the fatty acid moiety. Incorporation into cholesteryl esters was increased most during the development of atherosclerosis. Fatty acid synthesis was similar from both acetate-1-(14)C and the 2 carbon unit derived from glucose-2-(14)C, viz., predominantly de novo synthesis of fatty acids with 14 and 16 carbon atoms, and elongation for those of 18 carbons and longer. 相似文献
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The time course (0-60 min) of label incorporation from NaH14 CO3 into citric-acid-cycle intermediates and amino acids was investigated in incubations of isolated rat diaphragms. On the basis of these results, 14CO2 exchange by isocitrate dehydrogenase and 14CO2 fixation by propionyl-CoA carboxylation and pyruvate carboxylation could be estimated. Apparent rates amounted to about 30-40, 2, and 35 nmol/min per g of muscle, respectively. About 90 percent of C4-carbon compounds originating from 14CO2 fixation were subsequently removed by decarboxylation. 2-Cyano-4-hydroxycinnamate, an inhibitor of mitochondrial pyruvate transport, effectively reduced 14CO2 production from [1-14C]pyruvate but did not affect incorporation of radioactive label from NaH14CO3. In cell-free muscle extracts, 14CO2 fixation was demonstrable under assay conditions suitable for NADP -dependent 'malic' enzyme(s). Addition of hydroxymalonate, an inhibitor of the latter enzyme(s), significantly reduced 14CO2 incorporation. The results provide evidence for a continuous cytosolic replenishment and mitochondrial depletion of citric-acid-cycle carbon skeletons in resting skeletal muscle tissue. The functional role of malic (iso)enzyme activities in these processes is discussed. 相似文献
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Oxidative determination of 14C-labeled 2-oxo acids 总被引:2,自引:0,他引:2
A simple and rapid assay for the determination of 1-14C- or U-14C-labeled 2-oxo acids is described. It is based on the selective and complete oxidation of the carboxyl group to 14CO2. Preceding purification procedures are not necessary. In rat hindlimb perfusion studies, the procedure was used to develop an indirect method for the estimation of the intracellular dilution of [1-14C]pyruvate and to determine the relationship between the transamination and decarboxylation rates of leucine in the perfused tissue by the use of tracer doses of L-[1-14C]leucine. 相似文献
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H L Booij 《Canadian journal of biochemistry》1965,43(7):1011-1016