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1.
Thyroxine labeled with carbon-14 and iodine-125 was perfused through surviving rat hearts. Only when unlabeled triiodothyronine was added as a carrier could the newly formed doubly labeled triiodothyronine be isolated. The fact that this triiodothyronine was labeled with the correct ratio of carbon-14 to iodine-125 indicated that it originated from thyroxine. Approximately 5 percent of the initial carbon-14 radioactivity was found in the recovered triiodothyronine. 相似文献
2.
In organ cultures of intact rat pineal glands, N(6)O(2')-dibutyryl adenosine 3', 5'-monophosphate stimulates the conversion of tritiated trytophan to tritiated melatonin, as does L-norepinephrine. Potential sites of stimulation of melatonin production by dibutyryl cyclic adenosine monophosphate are discussed, based on observations that the dibutyryl analog also stimulates the conversion of serotonin labeled with carbon-14 to carbon-14-labeled melatonin without altering hydroxyin-dole-O-methyl transferase activity or intracellular accumulation of serotonin labeled with carbon-14. 相似文献
3.
Conversion of thyroxine to triiodothyronine in normal human subjects 总被引：13，自引：0，他引：13
The conversion of thyroxine to triiodothyronine, previously demonstrated in athyreotic human subjects, has been investigated in normal subjects who were given intravenous injections of purified thyroxine labeled with carbon-14 in ring A and in the alanine side chain. Evidence for the conversion of T4 to T3 was provided by the finding of carbon-14 in the T3 fraction isolated from serums. It is estimated that an appreciable fraction of T4 may be transformed to T3 in normal man. 相似文献
4.
Processes in the soil remain among the least well-characterized components of the carbon cycle. Arbuscular mycorrhizal (AM) fungi are ubiquitous root symbionts in many terrestrial ecosystems and account for a large fraction of photosynthate in a wide range of ecosystems; they therefore play a key role in the terrestrial carbon cycle. A large part of the fungal mycelium is outside the root (the extraradical mycelium, ERM) and, because of the dispersed growth pattern and the small diameter of the hyphae (<5 micrometers), exceptionally difficult to study quantitatively. Critically, the longevity of these fine hyphae has never been measured, although it is assumed to be short. To quantify carbon turnover in these hyphae, we exposed mycorrhizal plants to fossil ("carbon-14-dead") carbon dioxide and collected samples of ERM hyphae (up to 116 micrograms) over the following 29 days. Analyses of their carbon-14 content by accelerator mass spectrometry (AMS) showed that most ERM hyphae of AM fungi live, on average, 5 to 6 days. This high turnover rate reveals a large and rapid mycorrhizal pathway of carbon in the soil carbon cycle. 相似文献
5.
The results of two of the three biology experiments carried out on the Viking Mars landers have been simulated. The mixture of organic compounds labeled with carbon-14 used on Mars released carbon dioxide containing carbon-14 when reacted with a simulated martian surface and atmosphere exposed to ultraviolet light (labeled release experiment). Oxygen was released when metal peroxides or superoxides were treated with water (gas exchange experiment). The simulations suggest that the results of these two Viking experiments can be explained on the basis of reactions of the martian surface and atmosphere. 相似文献
6.
Oral administration to a dairy cow of Furadan insecticide (2,2-dimethyl-2,3-dihydro-7-benzofuranyl N-methylcarbamate) labeled with carbon-14 on the carbonyl produced in the milk certain radioactive materials which were not Furadan metabolites. The data suggest that these products were natural milk constituents containing only the carbon-14 atom from the Furadan molecule. Carbon-14-labeled carbon dioxide formed by the hydrolysis of the carbamate insecticide is the apparent precursor of these radiolabeled constituents of the milk. 相似文献
7.
Recent determinations of high production rates (up to 30 percent of primary production in surface waters) implicate free-living marine bacterioplankton as a link in a "microbial loop" that supplements phytoplankton as food for herbivores. An enclosed water column of 300 cubic meters was used to test the microbial loop hypothesis by following the fate of carbon-14-labeled bacterioplankton for over 50 days. Only 2 percent of the label initially fixed from carbon-14-labeled glucose by bacteria was present in larger organisms after 13 days, at which time about 20 percent of the total label added remained in the particulate fraction. Most of the label appeared to pass directly from particles smaller than 1 micrometer (heterotrophic bacterioplankton and some bacteriovores) to respired labeled carbon dioxide or to regenerated dissolved organic carbon-14. Secondary (and, by implication, primary) production by organisms smaller than 1 micrometer may not be an important food source in marine food chains. Bacterioplankton can be a sink for carbon in planktonic food webs and may serve principally as agents of nutrient regeneration rather than as food. 相似文献
8.
The isolation and purification of an immediate precursor of bacterial cellulose was confirmed with glucose randomly labeled with carbon-14. The glucose appears to be bound within the cell to a lipid, is carried across the bacterial cell wall, and is incorporated enzymatically into cellulose extracellularly. 相似文献
9.
Biosynthesis of a precursor (proparathyroid hormone) to human parathyroid hormone was demonstrated during incubation of tissue from parathyroid adenomas. The proparathyroid hormone is labeled more rapidly than parathyroid hormone during incubation with amino acids labeled with carbon-14 and is progressively converted to the hormone. Apparent differences in the relative rate of conversion of precursor to hormone found in different tumors suggest that proparathyroid hormone may accumulate in some of the tumors and be secreted into the circulation. 相似文献
10.
Cyclic adenosine monophosphate: stimulation of melatonin and serotonin synthesis in cultured rat pineals 总被引：3，自引：0，他引：3
Dibutyryl cyclic adenosine monophosphate, like norepinephrine, stimulates the synthesis of labeled melatonin and serotonin from tryptophan labeled with carbon-14 by rat pineals in organ culture. Unlike norepinephrine, dibutyryl cyclic adenosine monophosphate does not enhance the accumulation of labeled tryptophan or protein within the pineal. These findings are compatible with the hypothesis that cyclic adenosine monophosphate mediates some, but not all, of the effects of norepinephrine. 相似文献
11.
Cultured fibroblasts from a patient with gyrate atrophy of the retina do not convert L-ornithine, uniformly labeled with carbon-14, to proline. This metabolic block is caused by deficient L-ornithine:2-oxoacid aminotransferase activity in the patient. Her heterozygote father has intermediate activity of this enzyme. 相似文献
12.
Ascorbate sulfate: a urinary metabolite of ascorbic acid in man 总被引：4，自引：0，他引：4
E M Baker D C Hammer S C March B M Tolbert J E Canham 《Science (New York, N.Y.)》1971,173(999):826-827
Ascorbate-3-sulfate is a significant metabolite of ascorbic acid excreted in human urine. The characteristics of this compound were determined in experiments in which labeling with carbon-14 and tritium was used coupled with cochromatography with synthetic ascorbate-3-sulfate (both labeled and not labeled with sulfur-35) in a variety of solvent and absorbent systems. 相似文献
13.
Axonal delivery of neuroplasmic components to muscle cells 总被引：6，自引：0，他引：6
Substances labeled with phosphate-32 and carbon-14 and applied to hypoglossal nuclei in rabbits traveled down the hypoglossal nerves and after several days began entering only the muscle cells of the tongue. Prevention of axonal delivery on one side caused unilateral labeling of the tongue. Labeled substances delivered by extracellular fluids labeled all cells indiscriminately. The axonal conveyance of neuroplasmic components to peripheral cells may provide a basis for trophic influences of neurons on other cells. 相似文献
14.
Hormone-induced stabilization of soluble RNA in pea-stem tissue 总被引：2，自引：0，他引：2
When indoleacetic acid labeled with carbon-14 in the carboxyl group is fed to excised green pea-stem segments, growth is initiated, and there is a parallel progressive labeling of the RNA extracted by cold phenol. The bulk of the label is found in the 4S fraction. This fraction is more resistant to degradation by ribonuclease than a similar fractian obtained from tissue not treated with indoleacetic acid. 相似文献
15.
Tolerance to morphine-induced increases in [14C]catecholamine synthesis in mouse brain 总被引：1，自引：0，他引：1
C B Smith J E Villarreal J H Bednarczyk M I Sheldon 《Science (New York, N.Y.)》1970,170(962):1106-1108
Morphine sulfate increased the incorporation of carbon-14-labeled tyrosine into labeled catecholamines in the mouse brain. Tolerance was manifested by a shift to the right in the dose-response curve for morphine after mice were treated repeatedly with morphine. Naloxone, a specific morphine antagonist, also shifted the dose-response curve for morphine to the right. 相似文献
16.
Taylor RE Payen LA Gerow B Donahue DJ Zabel TH Jull AJ Damon PE 《Science (New York, N.Y.)》1983,220(4603):1271-1273
A morphologically modern human skeleton from Sunnyvale, California, previously dated by aspartic acid racemization to be approximately 70,000 years old and by uranium series isotopic ratios to be 8300 and 9000 years old, appears to be younger when dated by the carbon-14 method. Four carbon-14 determinations made by both decay and direct counting on three organic fractions of postcranial bone support a middle Holocene age assignment for the skeleton, probably in the range of 3500 to 5000 carbon-14 years before the present. This dating evidence is consistent with the geologic, archeological, and anthropometric relationships of the burial as well as previously determined carbon-14 determinations on associated materials. 相似文献
17.
Reexamination of glucose-6-phosphatase activity in the brain in vivo: no evidence for a futile cycle 总被引：5，自引：0，他引：5
T Nelson G Lucignani S Atlas A M Crane G A Dienel L Sokoloff 《Science (New York, N.Y.)》1985,229(4708):60-62
Glucose-6-phosphatase activity in the rat brain in vivo was estimated by measuring the differential loss of tritium and carbon-14 from the glucose pool labeled by a mixture of [2-3H]glucose and [U-14C]glucose. The results provide no evidence of significant dephosphorylation of glucose-6-phosphate and do not support the hypothesis of a futile cycle involving glucose-6-phosphatase activity in the brain. 相似文献
18.
Cimino G DE Rosa S DE Stefano S Sodano G Villani G 《Science (New York, N.Y.)》1983,219(4589):1237-1238
A biosynthetic experiment with mevalonic acid labeled with carbon-14 showed that the nudibranch Dendrodoris limbata elaborates polygodial, a sesquiterpenoid dialdehyde stored in the mantle, which constitutes its chemical defense against predators. Previously described nudibranchs drew defensive chemicals from their preys. 相似文献
19.
Beta thalassemia trait: detection at birth 总被引：1，自引：0，他引：1
The synthesis of alpha, beta, and gamma chains in samples of cord blood was measured by the incorporation of leucine labeled with carbon-14 into these chains. In a newborn affected with beta thalassemia trait, the presence of one beta thalassemia gene was revealed on the 1st day of life by the lower specific radioactivity of the beta chain. 相似文献
20.
Anaerobic biodegradation of DDT to DDD in soil 总被引：5，自引：0，他引：5
DDT labeled with carbon-14 was added to soil, and the mixture was incubated anaerobically for 2 weeks and 4 weeks. DDT and seven possible decomposition products were separated by thin-layer chromatography, and the radioactivity of material from individual spots was determined by liquid scintillation. The DDT was dechlorinated by soil microorganisms to DDD, and only traces of other degradation products were detected. No degradation of DDT was detected in sterile soil. 相似文献