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1.
Summary. This study investigated the in vitro effects of selected vitamins on nuclear L-tryptophan receptor binding of rat liver.
Our results revealed that some fat-soluble vitamins, β-carotene, retinyl acetate, calciferol, α-tocopherol, and Trolox, as well as some water-soluble vitamins, thiamine and riboflavin, acted to inhibit in vitro 3H-tryptophan binding to hepatic nuclei. On the other hand, pyridoxine had little or no effect. The addition of dithiothreitol,
a protective agent for sulfhydryl groups, along with each vitamin decreased the vitamin's inhibitory effect on in vitro 3H-tryptophan binding to nuclei, with the exception of riboflavin and calciferol. The addition of L-leucine, which alone had
no inhibitory effect on in vitro 3H-tryptophan binding to hepatic nuclei but when added with unlabeled L-tryptophan negated the effect of unlabeled L-tryptophan,
caused a markedly diminished inhibitory binding effect due to each of the following vitamins, thiamine, β-carotene, retinyl acetate, and α-tocopherol and Trolox, but no effect on riboflavin and calciferol.
Received December 29, 1999 Accepted March 8, 2000 相似文献
2.
Sidransky H Verney E Orenstein J 《American journal of physiology. Cell physiology》2000,278(6):C1237-C1245
This study was concerned with theeffects of NaCl administered in vivo or added in vitro to isolatednuclei on [3H]tryptophan binding to rat hepaticnuclei assayed in vitro. Hypertonic (10.7%) NaCl administered in vivoto rats caused at 10 min a marked decrease in in vitro binding (totaland specific) of [3H]tryptophan to hepaticnuclei. In vitro incubation of isolated hepatic nuclei, but not ofisolated nuclear envelopes, with added NaCl (particularly at 0.125 × 104 M and 0.25 × 104 M) revealed significant inhibition of[3H]tryptophan binding. However, isolatedhepatic nuclear envelopes prepared after in vitro incubation ofisolated nuclei with added NaCl did show inhibition of[3H]tryptophan binding (total and specific)compared with controls. Other salts (KCl, MgCl2,NaHCO3, NaC2H3O2, NaF,or Na2SO4), at similar concentrations to thatof NaCl except for MgCl2, when added to isolated nuclei didnot appreciably inhibit nuclear tryptophan binding. Kinetic studies ofin vitro nuclear [3H]tryptophan binding in thepresence of 0.125 × 104 M NaCl revealed thatbinding decreased at 0.5 h and continued to 2 h compared with nuclear[3H]tryptophan binding with controls (withoutNaCl addition). The results obtained in vivo in rats and those obtainedin vitro with isolated hepatic nuclei revealed NaCl-induced inhibitoryeffects on [3H]tryptophan binding to hepaticnuclei. Although the inhibitory effects were similar under the twodifferent experimental conditions, the mechanism for each may bedifferent in that the NaCl concentration in hepatic cells afteradministration of NaCl in vivo was appreciably higher than the lowlevels added in vitro to the isolated hepatic nuclei. 相似文献
3.
Summary The present experiments report differences in in vitro nuclear binding affinity for L-tryptophan 1) between livers of young (6 1/2 weeks old) and older (30 weeks old) NZBWF1 mice, but not so in similar aged Swiss mice, and also, 2) in livers of hamsters compared to livers of guinea pigs. In vitro hepatic nuclear specific binding affinity after tube-feeding L-tryptophan (520mg/100g body weight) to mice 1 h before killing revealed less in young than in older NZWBF1 mice, comparable to the above in vitro assay studies. In vitro nuclear binding affinity for L-tryptophan of livers of hamsters was significantly less than that of livers of guinea pigs or Swiss mice. In general, the degree of stimulatory effect on hepatic protein synthesis, as measured by in vitro [14C]leucine incorporation into protein using microsomes of animals tube-fed L-tryptophan 1 h before killing compared to that of animals tubefed water, correlated with the basal nuclear specific binding affinity to L-tryptophan of the animals (ages and species) used.This study was supported by U.S. Public Health Service Research Grant DK-45353 from the National Institute of Diabetes and Digestive and Kidney Diseases. 相似文献
4.
The flagella of the green alga Scherffelia dubia are covered by scales which consist of acidic polysaccharides and glycoproteins. Experimental deflagellation results in the
regeneration of flagella complete with scales. During flagellar regeneration, scales are newly synthesized in the Golgi apparatus,
exocytosed and deposited on the growing flagella. Flagellar regeneration is dependent upon protein synthesis and N-glycosylation,
as it is blocked by cycloheximide and partially inhibited by tunicamycin. Metabolic labeling with [35S]methionine/cysteine demonstrated that scale-associated proteins were not newly synthesized during flagellar regeneration,
suggesting that the proteins deposited on regenerating flagella were drawn from a pool. Quantitative immunoelectron microscopy
using a monospecific antibody directed against a scale-associated protein of 126 kDa (SAP126) revealed that the pool of SAP126
was primarily located at the plasma membrane, with minor labeling of the scale reticulum and trans-Golgi cisternae, both before deflagellation and during flagellar regeneration. Since SAP126 was sequestered during flagellar
regeneration into secretory vesicles together with newly synthesized scales, it is concluded that the persistent presence
of SAP126 in the trans-Golgi cisternae during scale biogenesis requires retrograde transport of the protein from the plasma membrane to the Golgi
apparatus.
Received: 3 July 1999 / Accepted: 21 August 1999 相似文献
5.
G. L. Chu G. Ross R. S. L. Wong R. Warters W. C. Dewey 《Journal of cellular physiology》1993,154(2):217-221
When nuclei were isolated from Chinese hamster ovary cells after being heated, there was a large increase in the amount of 3H-tryptophan labeled nonhistone protein in the nucleus relative to the whole cell. After 15 min or 30 min of heating at 45.5°C, the nuclear nonhistone protein content increased by 1.6 or 1.8, respectively. In contrast, when the nuclear nonhistone protein content was determined in the intact cell by using autoradiography to quantify 3H-tryptophan labeled protein in the nucleus and cytoplasm in sections of fixed cells, the nuclear nonhistone protein content increased by only 1.14 or 1.28 for 15 or 30 min at 45.5°C, respectively. Therefore, heat does not induce a massive movement of cytoplasmic protein into the nucleus. © 1993 Wiley-Liss, Inc. 相似文献
6.
Summary. The present study was designed to evaluate the relevance of arginine transport in nitric oxide (NO) synthesis in vascular
smooth muscle cells. For this purpose, NO synthesis and arginine transport (system B0,+ and y+) were evaluated in cells treated with IL-1β or angiotensin II (Ang II). In addition, the effects of 5 mM lysine and glutamine, competitive inhibitors of systems y+ and B0,+ respectively, were examined. L-arginine transport was estimated with 3H-labelled arginine and NO was determined with the Griess reagent. These studies were done in control conditions, arginine-starved
cells, and in cells incubated in media containing 10 mM arginine. Our data indicate that induction of NO biosynthesis by IL-1β
depends on external arginine when cells are arginine-depleted for 24 hours. The concentration of arginine producing half maximal
activation of NO synthesis in arginine-depleted cells ([arginine]i < 10 μM) was 41.1 ± 18 μM. By contrast, in normal culture conditions, NO synthesis occurred independently of arginine transport.
Neither 5 mM lysine or glutamine which abolished arginine transport through systems y+ and B0,+, respectively, reduced nitrite release in cells incubated in normal media. This suggests that the relevance of arginine uptake
to NO synthesis depends on the status of intracellular arginine pools. Intracellular arginine concentrations were not affected
by the stimulation of NO production using IL-1β or its inhibition using Ang II, but were markedly reduced by arginine starvation
for 48 h. Aspartate levels were also reduced by arginine-depletion, but were not affected in cells incubated with 10 mM arginine.
By contrast, glutamate levels were reduced in arginine-starved cells and were increased in cells incubated in arginine-supplemented
medium. Ornithine levels were markedly increased by arginine supplementation. Altogether, these findings indicate that NO
synthesis is normally independent of membrane transport. However in arginine-depleted cells, membrane transport is essential
for NO synthesis. It is concluded that arginine transport is required for the long-term maintenance of intracellular arginine
pools.
Received February 7, 1999; Accepted June 21, 1999 相似文献
7.
As a basis for understanding the role of non-histone proteins in nuclear differentiation, we have identified one period during embryogenesis when intense accumulation of non-histones occurs in nuclei of Rana pipiens. We then demonstrated, experimentally, the loss of non-histones from nuclei after transplantation into enucleated eggs. 3H-tryptophan or 3H-lysine was injected into blastocoeles of mid-blastulae and into archenterons of late gastrulae; embryos were subsequently studied autoradiographically. Nuclei of animal hemisphere cells from blastulae accumulated only small amounts of 3H-tryptophan within 3 h, whereas a large accumulation occurred in endodermal nuclei of gastrulae as early as 1 h, and after 3 h 95.9% (
) of the nuclei were densely labelled. Significant accumulation of 3H-lysine occurred in the majority of nuclei of both types within 3 h (blastulae
; gastrulae
). Controls, involving RNase or boiling TCA, demonstrated that the 3H-amino acids have been incorporated mainly into proteins. Endodermal nuclei labelled either with 3H-tryptophan or 3H-lysine after a 3 h incubation were transplanted singly into enucleated eggs. Autoradiograms demonstrated that most non-histones leave the nucleus during its reprogramming in the egg cytoplasm prior to first cleavage; whereas other types of proteins labelled with 3H-lysine remain for the most part in the nucleus. Cytochemical studies indicated that some of the non-histones which leave transplanted nuclei are acidic proteins; whereas some of those proteins which remain in the nucleus are histones.In addition to the above findings, the results of these studies demonstrate the feasibility in the future of studying the nucleocytoplasmic migration of different kinds of macromolecules in a developmental metazoan system and determining their roles in the establishment of nuclear differentiation. 相似文献
8.
Effects of high salt diets and taurine on the development of hypertension in the stroke-prone spontaneously hypertensive rat 总被引:3,自引:0,他引:3
Summary. Taurine is present in high concentrations in mammalian tissues and has been implicated in cardiovascular control mechanisms.
The aim of the present study was to evaluate the ability of taurine to attenuate salt-induced elevations in blood pressure
and markers of damage to the kidney and cardiovascular system in stroke prone spontaneously hypertensive rats (SPSHR). Male
SPSHR (6 weeks old) were placed on high salt diets that contained 1% (w/w) NaCl added to their normal chow for 84 days and
then were switched to 3% added NaCl for the remaining 63 days of the study. SPSHR was given 1.5% taurine in the drinking water
(n = 8), a taurine free diet (n = 8) or normal chow (n = 8). A final control group (n = 6) was not given high salt diets.
High salt diets caused an acceleration in the development of hypertension in all groups. Taurine supplementation reduced ventricular
hypertrophy and decreased urinary excretion of protein and creatinine. The taurine free diet did not alter serum or urinary
excretion of taurine, but did result in elevated urinary nitrogen excretion, increased serum cholesterol levels, and impaired
performance in a spatial learning task. Alterations in dietary taurine intake did not alter urinary or serum electrolytes
(Na+, K+), but taurine supplementation did attenuate a rise in serum calcium seen with the high salt diets. Urinary excretion (μg/24
h) of epinephrine and dopamine was significantly reduced in SPSHR given 1% NaCl in the diet, but this effect was not seen
in SPSHR on taurine free or supplemented diets. Taurine supplementation showed cardioprotective and renoprotective effects
in SPSHR given high salt diets.
Received April 12, 1999/Accepted September 13, 1999 相似文献
9.
The biosynthesis of galactan was investigated using microsomal membranes isolated from suspension-cultured cells of potato
(Solanum tuberosum L. var. AZY). Incubation of the microsomal membranes in the presence of UDP-[14C]galactose resulted in a radioactive product insoluble in 70% methanol. The product released only [14C]galactose upon acid hydrolysis. Treatment of the product with Aspergillus niger endo-1,4-β-galactanase released 65–70% of the radioactivity to a 70%-methanol-soluble fraction. To a minor extent, [14C]galactose was also incorporated into proteins, however these galactoproteins were not a substrate for Aspergillus niger endo-1,4-β-galactanase. Thus, the majority of the 14C-labelled product was 1,4-β-galactan. Compounds released by the endo-1,4-β-galactanase treatment were mainly [14C]galactose and [14C]galactobiose, indicating that the synthesized 1,4-β-galactan was longer than a trimer. In vitro synthesis of 1,4-β-galactan
was most active with 6-d-old cells, which are in the middle of the linear growth phase. The optimal synthesis occurred at
pH 6.0 in the presence of 7.5 mM Mn2+. Aspergillus aculeatus rhamnogalacturonase A digested at least 50% of the labelled product to smaller fragments of approx. 14 kDa, suggesting that
the synthesized [14C]galactan was attached to the endogenous rhamnogalacturonan I. When rhamnogalacturonase A digests of the labelled product
were subsequently treated with endo-1,4-β-galactanase, radioactivity was not only found as [14C]galactose or [14C]galactobiose but also as larger fragments. The larger fragments were likely the [14C]galactose or [14C]galactobiose still attached to the rhamnogalacturonan backbone since treatment with β-galactosidase together with endo-1,4-β-galactanase
digested all radioactivity to the fraction eluting as [14C]galactose. The data indicate that the majority of the [14C]galactan was attached directly to the rhamnose residues in rhamnogalacturonan I. Thus, isolated microsomal membranes contain
enzyme activities to both initiate and elongate 1,4-β-galactan sidechains in the endogenous pectic rhamnogalacturonan I.
Received: 24 June 1999 / Accepted: 30 August 1999 相似文献
10.
Nuclear protein synthesis in a temperature-sensitive Chinese hamster ovary cell line at 40 degrees C
We examined the incorporation of radioactive amino acids into nuclear proteins occurring at nonpermissive conditions in tsH1 Chinese hamster ovary cells with a temperature-sensitive defect in cytosol nonmitochondrial protein synthesis. In leucine-free medium at 40 degrees C, total cellular protein synthesis declined by 1-1.5%/min. As reported by others, preincubating these cells at 42 degrees C for 5-10 min sharply increased the rate of decline. The synthesis of acidic nuclear proteins at nonpermissive conditions (40 degrees C + 300 micrograms/ml cycloheximide) was demonstrated by the nuclear incorporation of 3H-tryptophan. Radioactivity, seen by autoradiography to be associated with these isolated Triton-X-100-washed nuclei, was released after incubating labelled nuclei with proteolytic enzymes. During incubation of tsH1 cells at nonpermissive conditions, pulse/chase experiments were consistent with the loss of some nuclear radioactivity into the cytoplasm. The distribution of cytosol and nuclear proteins, labelled at permissive or nonpermissive conditions and separated by isoelectric focusing, differed quantitatively and probably qualitatively, confirming the residual synthesis of acidic nuclear proteins at 40 degrees C in the presence of cycloheximide. Most newly synthesized acidic proteins retained by nuclei from cells labeled at nonpermissive conditions were present in a transciptionally active chromatin fraction. Although under these conditions the apparent rate of cellular RNA synthesis was unchanged, inhibiting residual cycloheximide-resistant nuclear protein synthesis with puromycin proportionately reduced RNA synthesis. Preincubating cells with 20 micrograms/ml of actinomycin D did not inhibit residual labelling of nuclear proteins; effects on residual nuclear labelling of impaired mitochondrial respiration were ambiguous. Nuclear proteins labelled under nonpermissive conditions probably included some of the 'prompt' heat shock proteins recently described. Provided certain assumptions are correct, our results are consistent with very limited protein synthesis associated with and even intrinsic to cell nuclei. They also suggest that this residual cycloheximide-resistant protein synthesis could be concerned with optimum synthesis or processing of certain nuclear RNA species. 相似文献
11.
Lorenz Poellinger Rabinder Nath Kurl Johan Lund Mikael Gillner Jan Carlstedt-Duke Bertil Högberg Jan-Ake Gustafsson 《Biochimica et Biophysica Acta (BBA)/General Subjects》1982,714(3):516-523
The intranuclear binding of radioactive 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in rat liver has been studied both in vivo and in vitro. Following the intravenous administration of [1,6-3H]TCDD, a maximum uptake by cell nuclei could be observed at 2 h after injection with a concurrent decrease in the cytosolic uptake. Using linear sucrose density gradient centrifugation, dextran-coated charcoal adsorption assay, DEAE-Sepharose ion-exchange chromatography, competition, enzymatic and saturation studies, a high-affinity binding protein for TCDD in liver cell nuclei could be demonstrated both in vivo and after an exchange in vitro of intravenously administered unlabelled 2,3,7,8- tetrachlorodibenzofuran (TCDBF) for [3H]TCDD. Sucrose density gradient analysis showed a size of 4–5 S for both the cytosolic and nuclear TCDD binding entity. The specific binding of [3H]TCDD to nuclear components was heat labile and saturable and had an equilibrium dissociation constant of 1.05 nM. Based on a differential susceptibility to specific hydrolases, i.e. DNAase, RNAase, trypsin and pronase, the binding entity appears to be a 4–5 S salt-extractable protein. 相似文献
12.
The role of cyclic electron transport has been re-examined in leaves of C3 plants because the bioenergetics of chloroplasts (H+/e = 3 in the presence of a Q-cycle; H+/ATP = 4 of ATP synthesis) had suggested that cyclic electron flow has no function in C3 photosynthesis. After light activation of pea leaves, the dark reduction of P700 (the donor pigment of PSI) following far-red
oxidation was much accelerated. This corresponded to loss of sensitivity of P700 to oxidation by far-red light and a large
increase in the number of electrons available to reduce P700+ in the dark. At low CO2 and O2 molar ratios, far-red light was capable of decreasing the activity of photosystem II (measured as the ratio of variable to
maximal chlorophyll fluorescence, Fv/Fm) and of increasing light scattering at 535 nm and zeaxanthin synthesis, indicating formation of a transthylakoid pH gradient.
Both the light-induced increase in the number of electrons capable of reducing far-red-oxidised P700 and the decline in Fv/Fm brought about by far-red in leaves were prevented by methyl viologen. Antimycin A inhibited CO2-dependent O2 evolution of pea leaves at saturating but not under limiting light; in its presence, far-red light failed to decrease Fv/Fm. The results indicate that cyclic electron flow regulates the quantum yield of photosystem II by decreasing the intrathylakoid
pH when there is a reduction in the availability of electron acceptors at the PSI level (e.g. during drought or cold stresses).
It also provides ATP for the carbon-reduction cycle under high light. Under these conditions, the Q-cycle is not able to maintain
a H+/e ratio of 3 for ATP synthesis: we suggest that the ratio is flexible, not obligatory.
Received: 23 February 1999 / Accepted: 19 August 1999 相似文献
13.
K. R. Straatman J. Nijsse H. Kieft A. C. van Aelst J. H. N. Schel 《Sexual plant reproduction》2000,13(1):43-51
Changes in nuclear pore complex (NPC) densities, NPCs/nucleus and NPCs/μm3, are described using freeze-fractured Brassica napus microspores and pollen in vivo and in vitro. Early stages of microspore- and pollen-derived embryogenic cells were also analysed.
The results of in vivo and in vitro pollen development indicate an increase in activity of the vegetative nucleus during maturation
of the pollen. At the onset of microspore and pollen culture, NPC density decreased from 15 NPCs/μm2 at the stage of isolation to 9 NPCs/μm2, under both embryogenic and non-embryogenic conditions. This implies that the drop in NPC density might be a result of culturing
the microspores and pollen rather than an indication for microspore and pollen embryogenesis in Brassica napus. However, after 1 day in culture under embryogenic conditions, the NPC density increased again and stabilised around 13 NPCs/μm2, whereas under non-embryogenic conditions the NPC density remained about 9 NPCs/μm2. This low density of 9 NPCs/μm2 was also found in the nuclei of sperm cells, in contrast to the 19 NPCs/μm2 found in the vegetative nucleus. It means that, although both the vegetative and sperm nuclei are believed to be metabolically
rather inactive in mature pollen, the NPC density of vegetative nucleus is twice as high as the NPC density of the sperm nuclei.
In a few cases, embryos formed suspensor-like structures with a NPC density of 9 NPCs/μm2, indicating a lower nucleocytoplasmic exchange of the nuclei of the suspensor cells than with the nuclei in the embryo proper.
In addition, observations on NPCs and other organelles, obtained by high resolution cryo-scanning microscopy, are presented.
Received: 29 December 1999 / Revision accepted: 3 March 2000 相似文献
14.
A. Draguhn G. Börner R. Beckmann K. Buchner U. Heinemann F. Hucho 《The Journal of membrane biology》1997,158(2):159-166
Eucaryotic nuclei are surrounded by a double-membrane system enclosing a central cisterna which is continuous with the endoplasmic
reticulum and serves as a calcium store for intracellular signaling. The envelope regulates protein and nucleic acid traffic
between the nucleus and the cytoplasm via nuclear pores. These protein tunnels cross through both nuclear membranes and are
permeable for large molecules. Surprisingly, patch clamp recordings from isolated nuclei of different cell species have revealed
a high resistance of the envelope, enabling tight seals and the resolution of single ion channel activity. Here we present
for the first time single-channel recordings from nuclei prepared from neuronal tissue. Nuclei isolated from rat cerebral
cortex displayed spontaneous long-lasting large conductances in the nucleus-attached mode as well as in excised patches. The
open times are in the range of seconds and channel activity increases with depolarization. The single-channel conductance
in symmetrical K+ is 166 pS. The channels are selective for cations with P
K/P
Na= 2. They are neither permeable to, nor gated by Ca2+. Thus, neuronal tissue nuclei contain a large conductance ion channel selective for monovalent cations which may contribute
to ionic homeostasis in the complex compartments surrounding these organelles.
Received: 12 November 1996/Revised: 18 February 1997 相似文献
15.
Patch-clamp experiments on isolated nuclei revealed the existence of ionic channels on the nuclear envelope, but their exact
localization and function are still unknown. Recent studies have demonstrated that ATP and calcium ions play an important
role in nucleocytoplasmic protein traffic. ATP is essential to allow big molecules in and out of the nucleus. However, a cytoplasmic
rise of calcium ions above 300 nm decreases both ATP-dependent transport and passive diffusion through the nuclear envelope. The use of isolated nuclei placed
in a saline solution provides the possibility for testing only the compounds added in the bath or in the recording pipette.
In the present study, we show that ATP is responsible for an increase of nuclear ionic permeability on isolated nuclei. This
result not only confirms data previously reported in in situ nuclei, but also suggests that ATP is directly involved in the modulation of passive ionic permeability. In these particular
experimental conditions, calcium ions decrease the channel current starting from a concentration of 1 μm. The parallelism in the modulation action of ATP and Ca++ between nuclear pores and ionic channels present on the nuclear envelope contributes to the support of the idea that an ionic
pathway is associated with the pore complex.
Received: 5 September 1996/Revised: 13 January 1997 相似文献
16.
H Sidransky E Verney J W Cosgrove A M Schwartz 《Biochemical medicine and metabolic biology》1992,47(3):270-273
Since some patients with eosinophilia-myalgia syndrome ingested tryptophan along with benzodiazepines, we investigated whether demoxepam, the N-desalkylated compound of chlordiazepoxide, would influence the binding of tryptophan to hepatic nuclei. L-Tryptophan has been shown to bind (saturable, stereospecific, and of high affinity) to rat hepatic nuclei and nuclear envelopes. We report that demoxepam has an inhibitory effect on in vitro [3H]tryptophan binding to rat hepatic nuclei and has an apparent KD approximately 22 microM. 相似文献
17.
Summary. Accumulation of amino acids was studied in rice roots of 3-day-old seedlings subjected for 48 h to anaerobic conditions.
Alanine and Gaba were the main amino acids accumulated under anoxia. Their synthesis was strongly inhibited by MSX and AZA,
inhibitors of glutamine synthetase and glutamate synthase. These activities increased after 8 h of anaerobic treatment and,
by immunoprecipitation of 35S-labeled proteins, it was shown that glutamine synthetase and ferredoxin-dependent glutamate synthase were synthesized during
the treatment. These findings indicate that the glutamine synthetase/glutamate synthase cycle play an important role in anaerobic
amino acid accumulation.
Received April 5, 1999 相似文献
18.
Oshima T 《Amino acids》2007,33(2):367-372
Summary. Recent research progress on polyamines in extreme thermophiles is reviewed. Extreme thermophiles produce two types of unique
polyamines; one is longer polyamines such as caldopentamine and caldohexamine, and the other is branched polyamines such as
tetrakis(3-aminopropyl)ammonium. The protein synthesis catalyzed by a cell-free extract of Thermus thermophilus, an extreme thermophile, required the presence of a polyamine and the highest activity was found in the presence of tetrakis(3-aminopropyl)ammonium.
In vitro experiments, longer polyamines efficiently stabilized double stranded nucleic acids and a branched polyamine, tetrakis(3-aminropyl)ammonium,
stabilized stem-and-loop structures. In T. thermophilus, polyamines are synthesized from arginine by a new metabolic pathway; arginine is converted to agmatine and then agmatine
is aminopropylated to N1-aminopropylagmatine which is converted to spermidine by an enzyme coded by a gene homologous to speB (a gene for agmatinase). In this new pathway spermidine is not synthesized from putrescine. Reverse genetic studies indicated
that the unique polyamines are synthesized from spermidine. 相似文献
19.
Interaction between the actions of taurine and angiotensin II 总被引:1,自引:0,他引:1
Summary. The amino acid, taurine, is an important nutrient found in very high concentration in excitable tissue. Cellular depletion
of taurine has been linked to developmental defects, retinal damage, immundeficiency, impaired cellular growth and the development
of a cardiomyopathy. These findings have encouraged the use of taurine in infant formula, nutritional supplements and energy
promoting drinks. Nonetheless, the use of taurine as a drug to treat specific diseases has been limited. One disease that
responds favorably to taurine therapy is congestive heart failure. In this review, we discuss three mechanisms that might
underlie the beneficial effect of taurine in heart failure. First, taurine promotes natriuresis and diuresis, presumably through
its osmoregulatory activity in the kidney, its modulation of atrial natriuretic factor secretion and its putative regulation
of vasopressin release. However, it remains to be determined whether taurine treatment promotes salt and water excretion in
humans with heart failure. Second, taurine mediates a modest positive inotropic effect by regulating [Na+]i and Na+/Ca2+ exchanger flux. Although this effect of taurine has not been examined in human tissue, it is significant that it bypasses
the major calcium transport defects found in the failing human heart. Third, taurine attenuates the actions of angiotensin
II on Ca2+ transport, protein synthesis and angiotensin II signaling. Through this mechanism taurine would be expected to minimize many
of the adverse actions of angiotensin II, including the induction of cardiac hypertrophy, volume overload and myocardial remodeling.
Since the ACE inhibitors are the mainstay in the treatment of congestive heart failure, this action of taurine is probably
very important.
Received November 10, 1998, Accepted May 19, 1999 相似文献
20.
The synthesis of DNA in nuclei and organellar nucleoids at the various stages of somatic embryogenesis in carrot (Daucus carota L. cv. Kurodagosun) was analyzed using anti-5-bromo-2′-deoxyuridine (BrdU) immunofluorescence microscopy. The active syntheses
of both nuclear and organellar DNA started in the cells forming the embryo proper 3 d after the initiation of embryogenesis,
but not in cells forming suspensor-like cell aggregates. In the early globular embryo, active DNA syntheses were continuously
observed in the whole embryo proper, except for the progenitor cells of the root apical meristem (RAM) and shoot apical meristem
(SAM). These were recognized as slowly cycling cells with a non-BrdU-labelled nucleus and strongly BrdU-labelled organellar
nucleoids. At the heart- and torpedo-shaped embryo stages, both nuclear and organellar DNA syntheses were inactive in the
presumptive RAM and SAM. Thus, slowing down of organellar DNA synthesis is not coupled with, but is later than, that of nuclear
DNA synthesis in the progenitor cells of the embryonic RAM and SAM. These findings clearly indicate that the timing of DNA
synthesis is similar in the progenitor cells of both the RAM and SAM in the early stages of somatic embryogenesis.
Received: 18 January 2000 / Accepted: 2 March 2000 相似文献