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 46 毫秒
1.
Two constitutive acetoacetyl-CoA (AcAc-CoA) reductases were purified from Methylobacterium rhodesianum MB 126, an NADPH-linked d(-)--hydroxybutyryl-CoA forming reductase (enzyme A) and an NADH-and NADPH-linked l(+)--hydroxybutyryl-CoA forming reductase (enzyme B). Enzyme A and B give apparent K m values of 15 M and 30 M for AcAc-CoA, 18 M for NADPH and 30 M for NADH, respectively. They are inhibited by AcAc-CoA at concentrations higher than 25 M and 50 M, respectively. The contribution of the two reductases to poly--hydroxybutyrate synthesis is discussed.  相似文献   

2.
In Fuji, the production of ethylene was increased with the addition of AgNO3 and inhibited with the addition of 10 M aminoethoxyvinylglycine (AVG). The addition of 80 M AgNO3 to transformed explants of Fuji cultured on selection medium resulted in increased ethylene production (20 l l–1) at 3 weeks. Under examining the effect of AgNO3 in Fuji, the 40 M AgNO3 showed with higher 33.8% and 6.5% in the efficiency of regeneration and transformation. However, ethylene production in Gala explants treated with 10M AgNO3 (3 l l–1) decreased after 2 weeks compared with the control (5 l l–1). Although the regeneration efficiency of Gala with 10 M AgNO3 was higher (41.1%) than the control (20.1%), there was no significant difference in the transformation efficiency at the same concentration. Shoot regeneration of Fuji and Gala was completely inhibited with 10 M AVG. These results suggest that the addition of AgNO3 affects the efficiency of Agrobacterium-mediated gene transfer in Fuji.Eun Soo Seong, Ill Min Chung- These two Authors Contributed equally to this work  相似文献   

3.
In chemostat cultures of Klebsiella pneumoniae (K. aerogenes) NCTC 418 we measured the concentrations of glucose and ammonium and we varied the ratio of the (limiting) concentrations of glucose and ammonium in the feed medium. By doing this at different dilution rates we found a range where growth rate varies with either concentration in the culture when the other concentration in the culture is held constant. This proves that within this range, dual-substrate controlled growth occurs. Dual substrate-controlled growth was accompanied by yield coefficients for glucose and for ammonium that were intermediate between the yield coefficients obtained for single glucose or single ammonium limitation. We quantified the control by either substrate in terms of the flux control coefficient with respect to that substrate, where flux refers to growth rate. Dualsubstrate controlled growth is reflected by the finding that both flux control coefficients exceed zero, simultaneously. In the transition of glucose to ammonium limitation, the control gradually shifts from glucose to ammonium.Abbreviations Symbol Units Meaning s Steady-state concentration of substrate in the culture - Sr M Concentration of substrate in reservoir medium - Y gDWmol-1 Yield - D h-1 Dilution rate - h–1 Specific growth rate - max h–1 Maximal growth rate - C 2 Control coefficient, of s on - J h-1 Rate or flux - JATP mmolgDW-1h-1 ATP synthesis rate - a Anabolism - c Catabolism - l Leak  相似文献   

4.
-Glucuronidase from callus cultures of Scutellaria baicalensis Georgi was purified to apparent homogeneity by fractionated ammonium-sulfate precipitation and chromatography on diethylaminoethyl-cellulose, hydroxylapatite and baicalin-conjugated Sepharose 6B. A 650-fold purification was obtained by this purification system. When subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis the purified protein migrated as a single band with a molecular mass of 55 kDa. We determined that the native enzyme has a molecular mass of 230 kDa using gel-filtration chromatography. These results suggested that the enzyme exists as a homotetramer composed of four identical 55-kDa subunits. The enzyme showed a broad pH optimum between 7.0 and 8.0. The K m values were 9 M, 10 M, 30 M and 40 M for luteolin 3 -O--d-glucuronide, baicalin, wogonin 7-O--d-glucoronide and oroxlin 7-O--d-glucuronide, respectively. The enzyme was most active with flavone 7-O--d-glucuronides.Abbreviations BA N6-benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - pI isoelectric point - R t retention time  相似文献   

5.
The distribution of mitochondria, their content and concentration (expressed as the ratio of the mean volume of mitochondria and the surface of the sensory axon) were determined in group-III and-IV nerve fibres innervating the knee joint capsule in the cat. Mitochondria mainly accumulated in axonal swellings (beads) and end bulbs of the terminal branches. Between single nerve fibres, marked differences in the content and the concentration of mitochondria were obtained in proximal portions (inside of the perineurium) and in distal portions (unmyelinated sensory endings). In group-III nerve fibres, the mitochondrial concentration ranged from 0.005 to 0.030 m3/m2 (proximal portion) and from 0.016 to 0.080 m3/m2 (distal portion). In unmyelinated group-IV nerve fibres, the values also showed a broad variation ranging from 0.001 to 0.011 m3/m2 (proximal portion) and from 0.003 to 0.019 m3/m2 (distal portion). The wide range of mitochondrial concentrations may reflect different energy consumption during receptive processes: nerve fibres with a low mechanical threshold and a high probability of excitatory events may be rich in mitochondria, whereas fibres with a high mechanical threshold and a low probability of excitatory events may be poor in mitochondria.  相似文献   

6.
Calcitonin gene-related peptide (CGRP) shares about 46% and 20% amino acid sequence homology with islet amyloid polypeptide (IAPP) and salmon calcitonin (sCT). We investigated whether these related peptides could cross-react with the specific binding of125I-[His]hCGRP I to the CGRP receptor in hamster insulinoma cell membranes. A rapid dissociation of membrane bound125I-[His]hCGRP I could be induced in the presence of 1 M chicken CGRP (cCGRP). The specific125I-[His]hCGRP I binding was inhibited by the related peptides and their half-maximal inhibitory concentrations (IC50) were: cCGRP (0.1 nM), rat CGRP I and human CGRP I and II (1.0–2.0 nM), fragment of hCGRP I (8-37) (150 nM), human IAPP (440 nM). The non-amidated form of hIAPP; human diabetes-associated peptide (hDAP) did not inhibit the binding of125I-[His]hCGRP I and sCT was only effective at a high concentration (1 M). Binding of125I-[His]hCGRP I was dose dependently inhibited by guanosine-5-O-(3-thiotriphosphate) or (GTPS) and a 70% reduction of binding was obtained with 0.1 mM GTPS. The IC50 value of cCGRP (0.1 nM) was increased 100-fold in the presence of 0.1 mM GTPS. Human CGRP I and cCGRP at 2.5 M did not stimulate the activity of hamster insulinoma cell membranes adenylate cyclase, while glucagon (1 M) induced a 2-fold increase. Thus, specific CGRP receptors present in hamster cells are associated with G protein (s) and IAPP can interact with these receptors. These results and the observation that cCGRP and hCGRP I did not influence adenylate cyclase activity provide further evidence for CGRP receptor subtypes.Abbreviations CGRP calcitonin gene-related peptide - IAPP islet amyloid polypeptide - IC50 half-maximal inhibitory concentration - GTPS guanosine-5-O-(3-thiotriphosphate) - 125I [His]hCGRP I, (2[125I]iodohistidyl10) human CGRP I  相似文献   

7.
Volume-sensitive taurine transport in fish erythrocytes   总被引:5,自引:0,他引:5  
Summary Taurine plays an important role in cell volume regulation in both vertebrates and invertebrates. Erythrocytes from two euryhaline fish species, the eel (Anguilla japonica) and the starry flounder (Platichthys stellatus) were found to contain high intracellular concentrations of this amino acid ( 30 mmol per liter of cell water). Kinetic studies established that the cells possessed a saturable high-affinity Na+-dependent -amino-acid transport system which also required Cl for activity (apparentK m (taurine) 75 and 80 m;V max 0.85 and 0.29 mol/g Hb per hr for eel (20°C) and flounder cells (10°C), respectively. This -system operated with an apparent Na+/Cl/taurine coupling ratio of 211. A reduction in extracellular osmolarity, leading to an increase in cell volume, reversibly decreased the activity of the transporter. In contrast, low medium osmolarity stimulated the activity of a Na+-independent nonsaturable transport route selective for taurine, -amino-n-butyric acid and small neutral amino acids, producing a net efflux of taurine from the cells. Neither component of taurine transport was detected in human erythrocytes. It is suggested that these functionally distinct transport routes participate in the osmotic regulation of intracellular taurine levels and hence contribute to the homeostatic regulation of cell volume. Volume-induced increases in Na+-independent taurine transport activity were suppressed by noradrenaline and 8-bromoadenosine-3, 5-cyclic monophosphate, but unaffected by the anticalmodulin drug, pimozide.  相似文献   

8.
At high growth rates, the biomass yield of bakers yeast (Saccharomyces cerevisiae) decreases due to the production of ethanol. For this reason, it is standard industrial practice to use a fed-batch process whereby the specific growth rate, , is fixed at a level below the point of ethanol production, i.e., crit. Optimally, growth should be maintained at crit, but in practice, this is difficult because crit is dependent upon strain and culture conditions. In this work, growth was maintained at a point just above crit by regulating ethanol concentration in the bioreactor. The models used for control design are shown, as are the experimental results obtained when this strategy was implemented. This technique should be applicable to all microorganisms that exhibit an overflow type metabolism.  相似文献   

9.
Three enzymes of the gibberellin (GA) biosynthetic pathway, a 7-oxidase, a 20-oxidase and a 3-hydroxylase, were partially purified from Cucurbita maxima endosperm by ammonium sulfate precipitation, gel-filtration and anion-exchange chromatography. The enzyme activities, which were assayed by the oxidation of GA12-aldehyde to GA12, of GA12 to GA15 (and GA24) and of GA15 to GA37, respectively, were completely separated from each other. The apparent molecular masses as estimated by gel-filtration high-performance liquid chromatography were 34.5 kDa for the 7-oxidase, 44.5 kDa for the 20-oxidase and 58 kDa for the 3-hydroxylase. The Michaelis-Menten constants (K m) were 8.6 M, 0.15M and 8.7 M for the respective substrates. All three enzymes had properties typical of 2-oxoglutarate dependent dioxygenases. 2-Oxoglutarate was essential for activity and served as a co-substrate, giving K m values of 6.1 M, 91 M and 41 M with the 7-oxidase, 20-oxidase and 3-hydroxylase, respectively. Furthermore, 2 oxo[5-14C]glutarate was oxidised stoichiometrically to [14C]succinate when the GA-substrates were oxidised to their respective products, and the 11 ratio was maintained under different oxygen concentrations. Approximately equimolar amounts of 14CO2 were released from 2-oxo[1-14C]glutarate when GA12 was oxidised to GA15/24 by the 20-oxidase. A crude enzyme preparation containing all three enzyme activities (and a 2-hydroxylase) converted GA12-aldehyde to [18O2]GA4 and [18O5]GA43 under 18O2, showing that all O-atoms incorporated after GA12-aldehyde originate from O2. Accordingly, the reaction rates were near zero under anaerobic conditions, although very low concentrations of O2 sufficed to sustain the reactions. Both Fe2+ and dithiothreitol stimulated the enzyme activities strongly, but if they were added together, catalase was needed to prevent inhibition. The pH dependence showed two opposite trends; the 7-oxidase was most active at pH 6 and below, whereas the other enzymes were maximally active above pH 6.5.Abbreviations BSA bovine serum albumin - GAn gibberellin An - DTT dithiothreitol - GC-MS combined gas chromatography-mass spectrometry - MeTMSi methyl ester trimethylsilyl ether We thank Mr. Keith Hall (Long Ashton) for assistance with the oxygen concentration measurements and Mrs. Gudrun Bodtke (Göttingen) and Mrs. Brigitte Schattenberg (Göttingen) for able technical assistance. The work was supported by the Deutsche Forschungsgemeinschaft, Germany, and the Agricultural and Food Research Council, UK, and by an Academic Research Collaboration award jointly from the Deutsche Akademische Austauschdienst (DAAD) and the British Council.  相似文献   

10.
Larval and adult Ambystoma tigrinum were subjected to acidosis by infusing lactic acid (2 M·g-1) into the peritoneal cavity. Blood was sampled at intervals to establish the time-course of the ensuing acidosis. Both larvae and adults became significantly acidotic after 1 h. The larval acidosis was more pronounced (-4 pH units versus-2 pH units) than adults due to greater extracellular buffering capacity (higher [HCO3 -]) in adults. Both forms recovered in about 8 h. Larvae showed a typical increase in circulating norepinephrine during the initial stages of the acidosis; adults did not, having significantly lower norepinephrine titer than larvae during the acidosis. Both larvae and adults showed transient increases in PO2 during the acidosis. The 1 and 2 antagonists, timolol and butoxamine respectively, (0.2 g·g-1) were administered to separate groups of larvae. Butoxamine (2) delayed the recovery from the acidosis by prolonging the increase in arterial PCO2 and reversing the recovery of [HCO3 -]. Timolol (1) did not delay recovery. We conclude that 2 receptors are involved in the catecholamine responses to acidosis in larvae. Catecholamines appear not to play the same role in adult acid-base disturbances as they seem to in larvae.Abbreviations RBC red blood cell  相似文献   

11.
Kim CS  Ji ES  Oh DK 《Biotechnology letters》2003,25(20):1769-1774
Kluyveromyces lactis -galactosidase gene, LAC4, was expressed in Escherichia coli as a soluble His-tagged recombinant enzyme under the optimized culture conditions. The expressed protein was multimeric with a subunit molecular mass of 118 kDa. The dimeric form of the -galactosidase was the major fraction but had a lower activity than those of the multimeric forms. The purified enzyme required Mn2+ for activity and was inactivated irreversibly by imidazole above 50 mM. The activity was optimal at 37 and 40 °C for o-nitrophenyl--d-galactopyranoside (oNPG) and lactose, respectively. The optimum pH value is 7. The K m and V max values of the purified enzyme for oNPG were 1.5 mM and 560 mol min–1 mg–1, and for lactose 20 mM and 570 mol min–1 mg–1, respectively.  相似文献   

12.
Formaldehyde accumulation ratios ([14CH2O]i/[14CH2O]o) as high as 12-fold were measured in anaerobic, CH3OH-energized, whole cell suspensions of the ribulose monophosphate (RuMP)-type methylotrophic strain T15. Uptake kinetics were extremely rapid, enabling the attainment of equilibrium in only 10–30 s. Transport appears to be energy-dependent and associated with the protonmotive force (pmf). Anaerobic incubation with 5 M carbonyl p-(trifluoromethoxy)-phenylhydrazone (FCCP) led to 70%–90% reduction of the accumulation ratio. Though not as pronounced, diminished uptake was also observed in the presence of 140 M nigericin, 161 M valinomycin and 90 mM KSCN, commensurate with their effects on pmf. Accumulation of CH2O as a function of external pH followed a trend more similar to that of pmf than either pH or . Preventing energization by incubation with 100 M N,N-dicyclohexylcarbodiimide (DCCD) led to nearly 80% inhibition of CH2O transport. Over short time periods it was possible to chase accumulated 14CH2O from previously loaded cells by collapsing pmf; however, this technique also indicated that significant 14CH2O incorporation began to occur within 3 min.Abbreviations FCCP Carbonyl cyanide p-(trifluoromethyoxy)-phenylhydrazone - DCCD N,N-dicyclohexylcarbodiimide - RuMP ribulose monophosphate - TPP+ tetra[U-14C]phenylphosphonium - pmf protonmotive force  相似文献   

13.
In hippocampal neurons, 5-hydroxytryptamine (5-HT) activates an inwardly rectifying K+ current via G protein. We identified the K+ channel activated by 5-HT (K5-HT channel) and studied the effects of G protein subunits and nucleotides on the K+ channel kinetics in adult rat hippocampal neurons. In inside-out patches with 10 m 5-HT in the pipette, application of GTP (100 m) to the cytoplasmic side of the membrane activated an inwardly rectifying K+ channel with a slope conductance of 36±1 pS (symmetrical 140 mm K+) at –60 mV and a mean open time of 1.1±0.1 msec (n=5). Transducin activated the (K5-HT) channels and this was reversed by -GDP. Whether the K5-HT channel was activated endogenously (GTP, GTPS) or exogenously (), the presence of 1 mm ATP resulted in a 4-fold increase in channel activity due in large part to the prolongation of the open time duration. These effects of ATP were irreversible and not mimicked by AMPPMP, suggesting that phosphorylation might be involved. However, inhibitors of protein kinases A and C (H-7, staurosporine) and tyrosine kinase (tyrphostin 25) failed to block the effect of ATP. These results show that G activates the G protein-gated K+ channel in hippocampal neurons, and that ATP modifies the gating kinetics of the channel, resulting in increased open probability via as yet unknown pathways.  相似文献   

14.
Two transgenic lines of mice were produced which contained the S Antilles- and 2-hemoglobin genes trandemly coupled to the micro locus control region (LCR). The LCRS Antilles2-hemoglobin transgenic mice expressed high levels of 2-hemoglobin while S Antilles-hemoglobin expression was virtually undetectable. Abundant 2-hemoglobin protein was observed in the blood of transgenic mice, while S Antilles-hemoglobin chains could not be detected. Transgenic red blood cells had substantially decreased sensitivity to osmotic lysis. Attempts to produce homozygotes containing the transgene were unsuccessful. The phenotype of these mice closely resembles that of -thalassemic mice. The LCRS Antilles2 transgenic mice demonstrate that if the LCR is coupled to the S Antilles- and 2-hemoglobin genes in tandem, only the distal 2-hemoglobin gene is selected for expression to significant levels in adult mice. These results support a reciprocally competitive model for LCR-hemoglobin developmental switching.  相似文献   

15.
This paper provides an approach for optimizing the cell density (Xc) and dilution rate (D) in a chemostat for a Pichia pastoris continuous fermentation for the extracellular production of a recombinant protein, interferon (INF-). The objective was to maximize the volumetric productivity (Q, mg INF- l–1 h–1), which was accomplished using response surface methodology (RSM) to model the response of Q as a function of Xc and D within the ranges 150 Xc 450 g cells (wet weight) l–1 and 0.1 mD0.9 m (m=0.0678 h–1, the maximum specific growth rate obtained from a fed-batch phase controlled with a methanol sensor). The methanol and medium feed rates that resulted in the desired Xc and D were determined based on the mass balance. From the RSM model, the optimal Xc and D were 328.9 g l–1 and 0.0333 h–1 for a maximum Q of 2.73 mg l–1 h–1. The model of specific production rate (, mg INF- g–1 cells h–1) was also established and showed the optimal Xc=287.7 g l–1 and D=0.0361 h–1 for the maximum (predicted to be 8.92×10–3 mg–1 g–1 h–1). The methanol specific consumption rate (, g methanol g–1 cells h–1) was calculated and shown to be independent of the cell density. The relationship between and (specific growth rate) was the same as that discovered from fed-batch fermentations of the same strain. The approach developed in this study is expected to be applicable to the optimization of continuous fermentations by other microorganisms.  相似文献   

16.
-Carotene synthesis was increased from a negligible amount to 152 mg (g-dry cells)–1 and H2O2 was accumulated up to 16.7 M during 2.5 day-culture of Blakeslea trispora. When cells were cultivated in 250 ml flasks containing various volumes (25–150 ml) of the medium, not only H2O2 accumulation but also -carotene synthesis increased as culture volume decreased. Addition of H2O2 (10 M) to the 1.5-day old cultures of B. trispora resulted in 46% higher -carotene synthesis than that without addition. All these results indicate that -carotene biosynthesis is stimulated by H2O2 in B. trispora.  相似文献   

17.
Efflux of glutathione (GSH) and GSH-conjugates from cultured rat liver epithelial cell lines; the non-tumorigenic ARL-15C1 and the -glutamyl transpeptidase containing, tumorigenic ARL-16T2, has been assessed under basal condition and during chronic treatment with 75 and 150 M ethacrynic acid (EA). The intracellular level of GSH increased in proportion to EA concentration during chronic exposure. The rates of GSH and GSH-EA conjugate efflux increased with intracellular GSH in both ARL cell lines.Glutathione-S-transferase activity measured with EA as substrate increased over the experimental time course after treatment with 150, but not 75 M EA. When intracellular GSH content was increased by treatment with the cysteine pro-drug, 2-L-oxothiazolidine 4-carboxylic acid, the rate of GSH efflux was increased, but not the rate of GS-EA conjugate export. Inhibition of -glutamyl transpeptidase by acivicin (AT-125) increased the GSH and GS-EA conjugate efflux rate in ARL-16T2 cells by factors of approximately 2 and 15, respectively. Acivicin treatment of ARL-16T2 cells chronically treated with EA elevated GSH efflux rate by 10-fold and GS-EA efflux by 40-fold versus control samples. These studies show that GSH and GSH conjugate efflux are accomplished as independently regulated processes. Efflux of GSH is enhanced by increased in racellular GSH, but increase in the conjugate transport rate requires the presence of the GSH conjugate. The response of the efflux process to treatment with a chronic GSH depleting agent was identical in two cell lines in which the metabolic fate of glutathione is known to differ fundamentally.Abbreviations GSH reduced glutathione - GSSG oxidized glutathione - GS-EA the glutathione conjugate of ethacrynic acid - EA ethacrynic acid - CDNB 1-chloro 2,4-dinitrobenzene - HBS HEPES buffered saline - OTC 2-L-oxothiazolidine 4-carboxylic acid - CYSSG cysteinyl-glutathione mixed disulfide - FDNB 1-fluoro-2,4-dinitrobenzene - GCS -glutamyl cysteine synthetase - GST glutathione-S-transferase - BCA bicinchoninic acid - SDS sodium dodecyl sulfate - PCA perchloric acid  相似文献   

18.
Recently, we proposed the hypothesis that a vicious cycle exists in human hibernating myocardium (HM) between the progression of myocyte degeneration and the development of fibrosis [1]. We now investigated the pathomechanism of this cycle in more detail and established a correlation between the severity of the morphological changes and the degree of postoperative functional recovery of HM.HM was diagnosed by dobutamine echocardiography, thallium-201 scintigraphy and radionuclide ventriculography. Functional recovery was present at 3 months after coronary bypass surgery but remained unchanged at 15 months. Forty patients were subdivided into 2 groups: A with complete and B with incomplete recovery. Biopsies taken during surgery and studied by electron microscopy, immunocytochemistry, rt-PCR, and morphometry revealed myocyte degeneration and inflammatory and fibrinogenic changes in a widened interstitial space. We report here for the first time an upregulation of TGF-1 evident by a 5-fold increase of fibroblasts and macrophages exhibiting a TGF-1 content 3-fold larger than in control, and a > 3-fold increase in TGF-1 mRNA by rt-PCR. The number of angiotensin converting enzyme (ACE) containing structures was increased (n/mm2: control - 11.4, A - 17.6, B - 19.2, control vs. A and B, p < 0.05). Fibrosis was more severe in group B than A or control (%: C - 10.1; A - 21.2; B - 40.6; p < 0.05). Capillary density was significantly reduced (n/mm2: C - 1152; A - 782; B - 579, p < 0.05) and intercapillary distance was widened (m: C - 29.5, A - 36.1, B - 43.3, p < 0.05). The number of CD 3 (n/mm2: C - 5.0; A - 9.6; B - 9.4, ns) and CD 68 positive cells (n/mm2: C - 37.2; A - 80.7; B - 55.0, C vs. A p < 0.05) was elevated in HM as compared to control indicating an inflammatory reaction. Cut-off points for functional recovery are fibrosis > 32%, capillary density < 660/mm2 and intercapillary distance > 39.0 m.In HM a self-perpetuating vicious cycle of tissue alterations leads to progressive replacement fibrosis and continuous intracellular degeneration which should be interrupted by early revascularization.  相似文献   

19.
Mouse B16 melanoma cells rapidly develop resistance to the antiproliferative effects of interferon (IFN) and interferon (IFN) when they are exposed to the interferons in vitro. This resistance was characterized to be non-genetic and dose-dependent, and does not alter other IFN-induced effects such as antiviral effects and elevation of 2,5-oligoadenylate synthetase activity in IFN-treated cells. The study of these IFN-resistant cells has been extended to an in vivo tumor model. Resistance, if it occurred in vivo, did not adversely affect the survival of IFN-treated mice. Further, IFN-treated mice inoculated with B16 cells that were resistant in vitro (B16res cells) survived significantly longer than IFN-treated mice inoculated with B16 cells that were sensitive in vitro. The IFN-treated B16res-inoculated mice had a significantly higher cure rate as well. The prolonged survival of the mice bearing B16res cell tumors did not seem to be caused by the slower growth rate of the B16res cells, since experiments performed with a tenfold higher B16res cell inoculum and a tenfold lower B16 cell inoculum did not show any change in the survival pattern. It is clear that in vitro resistant B16res cells are more sensitive to antitumor effects induced by IFN in vivo than in vitro sensitive B16 cells.Supported by U. S. Public Health Service grant no. CA50752 awarded by the National Cancer Institute, Department of Health and Human Services (W. R. F.) and by a James W. McLaughlin Fellowship (C. M. F.)  相似文献   

20.
When serum-starved A431 cells were treated with 200 nM phorbol ester TPA for 15 min, the cellular activity of protein kinase FA/glycogen synthase kinase-3 (kinase FA/GSK-3) could be decreased to ~25% of control. Conversely, when treated with 1 M TPA for 24 hr, the activity could be reversibly increased to ~200% of Control. The naturally occurring protein kinase C (PKC) inhibitor sphingosine at a concentration of 27 M could also induce activation of kinase FA/GSK-3 to ~200% of control within 60 min. Further, when cells were chronically treated with 1 M TPA for 24 hr and then with 27 M sphingosine for 60 min, the activity of kinase FA/GSK-3 could only be increased to ~200% of control. Furthermore, when cells were pretreated with sphingosine and then acutely treated with TPA, the acute TPA effect on kinase FA/GSK-3 activity could be abolished by genistein or tyrosine phosphorylation, which could be blocked by genistein or tyrosine phosphatase, but could be reversed by orthovanadate. Taken together, the results demonstrate that TPA/sphingosine induce tyrosine phosphorylation and concurrent activation of kinase FA/GSK-3 in a common signalling pathway. Since TPA and sphingosine are potent PKC modulators, the results further suggest a potential role of PKC in modulating tyrosine phosphorylation/activation of kinase FA/GSK-3. Kinetic studies on seven subtypes of PKC further demonstrate a specific involvement of PKC in this tyrosine phosphorylation/activation process. This provides a new mode of signal transduction between these two important serine/threonine kinases in cells.  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