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1.
Reyhan Gul Guven Alevcan Kaplan Kemal Guven Fatma Matpan Mehmet Dogru 《Biotechnology and Bioprocess Engineering》2011,16(1):114-119
β-Galactosidase purified from the thermoacidophilic Alicyclobacillus acidocaldarius subsp. rittmannii isolated from Antarctica is a member of the GH42 family. The enzyme was not effected by various concentrations of its reaction
product glucose, but was greatly inhibited by the other reaction product galactose using both substrates, ONPG and lactose.
Linewever-Burk plot analysis derived from both ONPG and lactose hydrolysis results showed that galactose is a mixed-type inhibitor
of the purified β-galactosidase. The enzyme was slightly activated by Mg2+ (13% at 20 mM), while inhibited at higher concentrations of Ca+2 (33% at 10 mM), Zn+2 (86% at 8 mM) and Cu+2 (87% at 4 mM). The enzyme activity was not significantly altered by the metal ion chelators EDTA and 1,10-phenanthroline
up to 20 mM, indicating that this enzyme is not a metalloenzyme. 2-Mercaptoethanol and DTT were found to enhance β-galactosidase
activity, while p-chloromercuribenzoic acid (PCMB) completely inhibited enzymatic activity (97% at 1 mM; 99.7% at 2 mM), indicating
at least one essential Cys residue modified by the reagents in the active site of β-galactosidase. Iodoacetamide and Nethylmaleimide
had little effect on the β-galactosidase. Phenylmethylsulfonyl fluoride (PMSF) inhibited the enzyme strongly (19.8% at 1 mM;
71.9% at 10 mM), also showing the participation of serine for enzyme activity. 相似文献
2.
M.L. Helmich-de Jong S.E. van Emst-de Vries J.J.H.H.M. De Pont F.M.A.H. Schuurmans Stekhoven S.L. Bonting 《生物化学与生物物理学报:生物膜》1985,821(3)
Direct evidence for the occurrence of an ADP-sensitive phosphoenzyme of (K+ + H+)-ATPase, the proton-pumping system of the gastric parietal cell is presented. The enzyme is phosphorylated with 5 μM [γ-32P]ATP in 50 mM imidazole-HCl (pH 7.0) and in the presence of 7–15 μM Mg2+. Addition of 5 mM ADP to this preparation greatly accelerates its hydrolysis. We have been able to establish this by stopping the phosphorylation with radioactive ATP, by adding 1 mM non-radioactive ATP, which leads to a slow monoexponential process of dephosphorylation of 32P-labeled enzyme. The relative proportion of the ADP-sensitive phosphoenzyme is 22% of the total phosphoenzyme. Values for the rate constants of breakdown and interconversion of the two phosphoenzyme forms have been determined. 相似文献
3.
Inhibition of electron transport activities in the spheroplasts ofSynechococcus 6301 by HgCl2 is dependent on the concentration of mercury ions. The inhibition of whole chain electron transport activity occurs at low
concentration of Hg2+ (6 ΜM@#@). This inhibition occurs mostly due to interaction of Hg2+ on plastocyanin. At an elevated concentration (24 ΜM@#@), mercury induces inhibition chiefly in photosystem II catalyzed electron transport. At this concentration it also alters
both the absorption and emission characteristics of the phycocyanin. The photosystem I catalyzed electron transport was inhibited
by 50% only at high concentrations (36 ΜM@#@) of HgCl2. However, electron transport catalyzed by photosystems I and II from reduced duroquinone to methylviologen which involves
intersystem electron transport is extremely sensitive to mercury (low concentration 6–9 ΜM) like that of whole chain assay
indicating that the observed inhibition in whole chain electron transport at low concentrations is mostly contributed by the
damage involving other intersystem electron transport carrier(s) like plastocyanin. Thus mercury ions depending on the concentration
affects the electron transport at multiple sites in the spheroplasts ofSynechococcus. 相似文献
4.
Ajmalicine production in methyl jasmonate-induced Catharanthus roseus cell cultures depends on Ca2+ level 总被引:1,自引:0,他引:1
Cytosolic Ca2+ and jasmonate mediate signals that induce defense responses in plants. In this study, the interaction between Ca2+ and methyl jasmonate (MJ) in modulating defense responses was investigated by monitoring ajmalicine production in Catharanthus roseus suspension cultures. C. roseus suspensions were treated with nine combinations of CaCl2 (3, 23, and 43 mM) and MJ (0, 10, and 100 μM) on day 6 of growth. Increased Ca2+ influx through the addition of extracellular CaCl2 suppressed ajmalicine production in MJ-induced cultures. The highest ajmalicine production (4.75 mg/l) was observed when
cells were treated with a low level of calcium (3 mM) combined with a high level of MJ (100 μM). In the presence of 3 mM CaCl2 in the medium, the addition of Ca2+ chelator EGTA (1, 2.5, and 5 mM) or Ca2+ channel blocker verapamil (1, 10, and 50 μM) to MJ-induced (100 μM) cultures on day 6 also inhibited ajmalicine production
at higher levels of the Ca2+ inhibitors. Hence, ajmalicine production in MJ-induced C. roseus cultures depended on the intracellular Ca2+ concentration and a low extracellular Ca2+ concentration (3 mM) enhanced MJ-induced ajmalicine production. 相似文献
5.
K+-conductive pathways were evaluated in isolated surface and crypt colonic cells, by measuring 86Rb efflux. In crypt cells, basal K+ efflux (rate constant: 0.24 ± 0.044 min−1, span: 24 ± 1.3%) was inhibited by 30 mM TEA and 5 mM Ba2+ in an additive way, suggesting the existence of two different conductive pathways. Basal efflux was insensitive to apamin,
iberiotoxin, charybdotoxin and clotrimazole. Ionomycin (5 μM) stimulated K+ efflux, increasing the rate constant to 0.65 ± 0.007 min−1 and the span to 83 ± 3.2%. Ionomycin-induced K+ efflux was inhibited by clotrimazole (IC50 of 25 ± 0.4 μM) and charybdotoxin (IC50 of 65 ± 5.0 nM) and was insensitive to TEA, Ba2+, apamin and iberiotoxin, suggesting that this conductive pathway is related to the Ca2+-activated intermediate-conductance K+ channels (IKca). Absence of extracellular Ca2+ did neither affect basal nor ionomycin-induced K+ efflux. However, intracellular Ca2+ depletion totally inhibited the ionomycin-induced K+ efflux, indicating that the activation of these K+ channels mainly depends on intracellular calcium liberation. K+ efflux was stimulated by intracellular Ca2+ with an EC50 of 1.1 ± 0.04 μM. In surface cells, K+ efflux (rate constant: 0.17 ± 0.027 min−1; span: 25 ± 3.4%) was insensitive to TEA and Ba2+. However, ionomycin induced K+ efflux with characteristics identical to that observed in crypt cells. In conclusion, both surface and crypt cells present
IKCa channels but only crypt cells have TEA- and Ba2+-sensitive conductive pathways, which would determine their participation in colonic K+ secretion. 相似文献
6.
M. N. Nenov A. V. Berezhnov E. I. Fedotova K. S. Grushin O. Yu. Pimenov A. N. Murashev V. P. Zinchenko Yu. M. Kokoz 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2010,4(4):374-382
The “arginine paradox” in cardiomyocytes isolated from the left ventricle of Spraque Dawlay (SD) and spontaneously hypertensive
rats (SHR) was studied. With 1 mM L-arginine in the bath, the addition of 5 mM L-arginine to incubation medium increased NO production and inhibited amplitude of L-type Ca2+ currents in SD cardiomyocytes. A variety of compounds, including the antagonist of α2-adrenoceptors yohimbine and inhibitors of PI3 kinase (wortmanine), NO synthase (7NI), and cGMP-dependent protein kinase (KT5823),
dramatically weakened the inhibitory effects of 5 mM L-arginine on Ca2+ currents. The agonist of α2-adrenoceptors guanabenz acetate increased NO production and inhibited Ca2+ currents, while wortmanine, 7NI, and KT5823 antagonized guanabenz. In SHR cardiomyocytes, the “arginine paradox” was not
observed: 5 mM L-arginine affected neither NO production nor Ca2+ currents. Consistently, guanabenz acetate did not alter NO production and inhibited Ca2+ currents to a much smaller extent in SHR cardiomyocytes as compared to SD cardiomyocytes. Taken together, the data of the
inhibitory analysis suggest that millimolar L-arginine serves as an agonist of α2-adrenoceptors, which are coupled to PI3K-Akt pathway as well as downstream NO-cGMP pathway to control activity of L-type
Ca2+ channels, thus providing new insights into the “arginine paradox” in cardiomyocytes. 相似文献
7.
Release of an acid phosphatase activity during lily pollen tube growth involves components of the secretory pathway 总被引:2,自引:0,他引:2
Ibrahim H Pertl H Pittertschatscher K Fadl-Allah E el-Shahed A Bentrup FW Obermeyer G 《Protoplasma》2002,219(3-4):176-183
Summary. An acid phosphatase (acPAse) activity was released during germination and tube growth of pollen of Lilium longiflorum Thunb. By inhibiting components of the secretory pathway, the export of the acPase activity was affected and tube growth
stopped. Brefeldin A (1 μM) and cytochalasin D (1 μM), which block the production and transport of secretory vesicles, respectively,
inhibited the acPase secretion. The Ca2+ channel blocker gadolinium (100 μM Gd3+) also inhibited acPase secretion and tube growth, whereas 3 mM caffeine, another Ca2+ uptake inhibitor, stimulated the acPase release, while tube growth was inhibited. The Yariv reagent (β-D-glucosyl)3 Yariv phenylglycoside stopped tube growth by binding to arabinogalactan proteins of the tube tip cell wall but did not affect
acPase secretion. A strong correlation between tube growth and acPase release was detected. The secreted acPase activity had
a pH optimum at pH 5.5, a K
M of 0.4 mM for p-nitrophenyl phosphate, and was inhibited by zinc, molybdate, phosphate, and fluoride ions, but not by tartrate. In electrophoresis
gels the main acPase activity was detected at 32 kDa. The conspicuous correlation between activity of the secretory pathway
and acPase secretion during tube elongation strongly indicates an important role of the acPase during pollen tube growth and
the secreted acPase activity may serve as a useful marker enzyme assay for secretory activity in pollen tubes
Received July 25, 2001 Accepted January 15, 2002 相似文献
8.
Laticifers differentiation in callus cultures of Calotropis procera (Asclepiadaceae) as affected by own latex and its fractions incorporated in Murashige and Skoog (MS) medium is described. Callus cultures
have been maintained on MS medium with 2.3 ΜM 6-furfurylaminopurine (FAP) and 3.0 ΜM 1-naphthylacetic acid (NAA). Marked increase
in laticifers differentiation (from 10.1 to 28.4 %) was observed on this medium supplemented with 1 % (v/v) of latex. Latex
fractions containing proteins + complex polysaccharides or inorganic salts also increased laticifers differentiation (by 21.8
% and 24.1 %, respectively). Other fractions (free amino acid + saccharides, phenols and terpenes + sterols) had no marked
effect on laticifers differentiation while alkaloid fraction inhibited it. Effect of latex on laticifers differentiation was
much more profound than the reported optimal concentration of plant growth regulators (4.6 ΜM FAP + 1 ΜM IAA).
This research was supported by grant-in-aid for research from the University Grants Commission (No. F3-65/91SR II), New Delhi,
to Dr. KG. Ramawat. 相似文献
9.
An exo-β-d-glucosaminidase gene (PH0511) was cloned from the hyperthermophilic archaeon, Pyrococcus horikoshii, and expressed in Escherichia coli. The purified protein showed a strong exo-β-d-glucosaminidase activity by TLC analysis. DTT (50 mM) had little effect on its homodimeric structure during SDS-PAGE. The enzyme was optimally active at 90°C (over 20 min) and pH 6. It had a half-life of 9 h at 90°C and is the most thermostable glucosaminidase described up to now. The activity was not inhibited by ethanol, 2-propanol, DMSO, PEG-400, denaturing agents SDS (5%, w/v), urea, guanidine hydrochloride (5 M) and Mg2+, Mn2+, Co2+, Ca2+, Sr2+, Ni2+ (at up to 10 mM). 相似文献
10.
Takashi Imanishi Kayoko Matsushima Akinori Kawaguchi Hajime Asano Yoshinori Funakami Tetsuyuki Wada Takashi Masuko Shigeru Yoshida Seiji Ichida 《Neurochemical research》2009,34(5):1011-1019
Characteristics for the up-regulated response in the concentration of intracellular calcium ion ([Ca2+]
i
) and in the sodium ion (Na+) current by serotonin (5-HT) were investigated in differentiated neuroblastoma × glioma hybrid NG108-15 (NG) cells. The results
for the changes in [Ca2+]
i
by 5-HT were as follows, (1) The 5-HT-induced Ca2+ response was inhibited by 3 × 10−9 M tropisetron (a 5-HT3 receptor blocker), but not by other types of 5-HT receptor blockers; (2) The 5-HT-induced Ca2+ response was mainly inhibited by calciseptine (a L-type Ca2+ blocker), but not by other types of Ca2+ channel blockers or 10−7 M TTX (a voltage-sensitive Na+ channel blocker); (3) When the extracellular Na+ was removed by exchange with choline chloride or N-methyl-d-glucamine, the 5-HT-induced Ca2+ response was extremely inhibited. The results for the 5-HT-induced Na+ current by the whole cell patch-clamp technique were as follows, (1) The 5-HT-induced Na+ current in differentiated cells was significantly larger than that in undifferentiated cells; (2) The ED50 value for 5-HT-induced Na+ current in undifferentiated and differentiated cells was almost the same, about 4 × 10−6 M each other; (3) The 5-HT-induced Na+ current was completely blocked by 3 × 10−9 M tropisetron, but not by other 5-HT receptor antagonists and 10−7 M TTX. These results suggested that 5-HT-induced Ca2+ response in differentiated NG cells was mainly due to L-type voltage-gated Ca2+ channels allowing extracellular Na+ to enter via 5-HT3 receptors, but not through voltage-gated Na+ channels. 相似文献
11.
Summary A metalloprotease from sorghum malt variety KSV8-I was purified by a combination of 4-M sucrose fractionation, ion-exchange
chromatography on Q-Sepharose (Fast flow), gel-filtration chromatography on Sephadex G-100 and hydrophobic interaction chromatography
on phenyl-Sepharose CL-4B. The enzyme was purified 7.9-fold to give a 13.4% yield relative to the total activity in the crude
extract and a final specific activity of 2128.7 U mg−1 protein. SDS-PAGE revealed a single migrating protein band corresponding to a relative molecular mass of 35 kDa. The purified
enzyme had optimal activity at 60 °C and maximal temperature stability between 40 and 60 °C but retained over 77% of its initial
activity after incubation at 70 °C for 30 min. Both pH optimum and maximal stability were at 7.0 but 60% of the activity remained
after 24 h between pH 5.0 and 8.0. Using 0.2 ml of 5 mM solution of each metal ion, the purified protease was slightly (P<0.05) inhibited by Zn2+, appreciably (P<0.01) inhibited by Ca2+ and Co2+ and highly significantly (P<0.001) inhibited by Ag+, Ba2+, Hg2+, Mn2+ and Pb2+. The enzyme was equally highly significantly (P<0.001) inhibited by EDTA and hydrolysed casein to give the following kinetic constants: Km = 21.0 mg ml−1; Vmax = 8.2 μmol ml1 min−1 and Ki = 0.390 mM. 相似文献
12.
The DR2356 nudix hydrolase gene from Deinococcus radiodurans has been cloned and the product expressed as an 18 kDa histidine-tagged protein. The enzyme hydrolysed adenosine and diadenosine polyphosphates, always generating ATP as one of the initial products. ATP and other (deoxy)nucleoside triphosphates were also substrates, yielding (d)NDP and Pi as products. The DR2356 protein was most active at pH 8.6–9.0 and showed a strong preference for Mn2+ as activating cation. Mg2+ ions at 15 mM supported only 5% of the activity achieved with 2 mM Mn2+. K
m and k
cat values for diadenosine tetra-, penta- and hexaphosphates were 2.0, 2.4 and 1.1 μM and 11.4, 28.6 and 12.0 s−1, respectively, while for GTP they were 20.3 μM and 1.8 s−1, respectively. The K
m for adenosine 5′-pentaphosphate was <1 μM. Expression analysis showed the DR2356 gene to be induced eight- to ninefold in stationary phase and in cells subjected to slow dehydration plus rehydration. Superoxide (but not peroxide) treatment and rapid dehydration caused a two-to threefold induction. The Mn-requirement and induction in stationary phase suggest that DR2356 may have a specific role in maintenance mode metabolism in stationary phase as Mn2+ accumulates. 相似文献
13.
The calcium-sensitive forms of adenylyl cyclases (AC) have been revealed in the majority of vertebrate and invertebrate animals,
as well as in several representatives of unicellular organisms, including infusoria. We have found for the first time that
the AC activity in the infusorian Tetrahymena pyriformis changes in the presence of calcium ions. Calcium ions at concentrations of 0.2–20 μM stimulated the activity of this enzyme,
with the maximum of the stimulatory effect being observed at 2 μM Ca2+. At a concentration of 100 μM and higher, the calcium cations inhibited the AC activity. Antagonists of calmodulin W-5 and
W-7 at concentrations of 20–100 μM decreased the stimulatory effect of 5 μM Ca2+, while at the higher concentrations inhibited it completely. Another calmodulin antagonist, chloropromazine, decreased the
Ca2+-stimulated AC activity only at concentrations of 200–1000 μM. The stimulatory effect of serotonin, EGF, and cAMP on AC activity
was enhanced in the presence of 5 μM Ca2+. The stimulatory effect of EGF, cAMP, and insulin on AC was decreased in the presence of 100 μM Ca2+, while the effect of cAMP was also observed in the presence of calmodulin antagonists (500 μM). At the same time, stimulatory
effect of D-glucose did not change in the presence of Ca2+ and calmodulin antagonists. The obtained data indicate that, in the infusorian T. pyriformis, there are calcium-sensitive forms of AC that can be stimulated by EGF, cAMP, insulin, and serotonin. 相似文献
14.
Elevation of the external potassium concentration induced a two-phase inward current in freshly isolated pyramidal hippocampal
neurons. This current was voltage-dependent and demonstrated strong inward rectification. The current consisted of a leakage
current and a time-dependent current (τ=40–50 msec at 21°C); the latter was designated asI
ΔK. As was shown earlier, K+ is a major charge carrier in the development of slow potassium-activated current. The pharmacological properties ofI
ΔK were studied using a patch-clamp technique.I
ΔK was completely blocked by external 10 mM TEA or 5 mM Ba2+ (IC50=480±90mM) and exhibited low sensitivity to extracellular Cs+ (2 mM). This current was not affected by 1 mM 4-aminopyridine and was insensitive to a muscarinic agonist, carbachol (50
μM), and to 1 mM extracellular Cd2+. Elevation of external Ca2+ from 2.5 mM to 10 mM did not changeI
ΔK. Our data indicate that the pharmacological properties ofI
ΔK differ from those of other voltage-gated potassium currents, but more specific blockers must be used to make this evidence
conclusive. 相似文献
15.
We have identified two types of invertases, one bound ionically and the other covalently to the particulate fraction in grains
of heat tolerant C 306 and heat susceptible WH 542 cultivars of wheat (Triticum aestivum L.). The cell walls contained a high level of invertase activity, of which 79.2–72.8% was extractable by 2 M NaCl and 14.9–21.1%
by 0.5% EDTA in C 306 and WH 542, respectively. The NaCl-released invertase constituted the predominant fraction. Using 5–100 mM
sucrose and pH range of 4.0–7.0, the apparent Michaelis constant (K
m, enzyme substrate affinity measure) of enzyme ranged from 5.73 to 16.06 mM for C 306 and from 6.08 to 19.86 mM for WH 542.
The V
max (maximum catalytic rate) values at these pH were higher in C 306 (0.63–11.04 μg sucrose hydrolysed min−1) than WH 542 (0.51–8.73 μg sucrose hydrolysed min−1). By employing photo-oxidation and by studying the effect of pH on K
m and V
max, the involvement of histidine and α-carboxyl groups at the active site of the enzyme was indicated. The two cultivars also
showed differential response in terms of thermodynamic properties of the enzyme i.e. energy of activation (E
a), enthalpy change (ΔH) and entropy change (ΔS). NaCl-released invertase showed differential response to metal ions in two cultivars suggesting their distinctive nature.
Mn2+, Cu2+, Hg2+, Mg2+, Zn2+ and Cd2+ were strong inhibitors in WH 542 as compared to C 306 while K+, Ca2+ were stimulators in both the cultivars. Overall the results suggest that genetic differences exist in wall bound invertase
properties of wheat grains as evident in its altered kinetic behaviour. 相似文献
16.
I. V. Shemarova E. B. Maizel’ A. E. Khovanskikh 《Journal of Evolutionary Biochemistry and Physiology》2000,36(2):111-117
Effects of cadmium cations in free (Cd2+) and chelated with EDTA (Cd2+-EDTA) forms were studied on growth, endocytosis, and activity of glutathione S-transferase (GT) in the free-living infusoriaTetrahymena pyriformis. It is shown that the cytotoxicity of Cd2+ in the free form at a concentration of 10 μM is much higher than of the Cd2+-EDTA complex at the equimolar concentration. Even at a low concentration (2 μM), Cd2+ produces an inhibition of the growth rate and endocytosis in theT. pyriformis culture, while the Cd2+-EDTA complex suppresses these functions insignificantly. Cd2+ in the free form at concentrations of 10 and 100 μM reduced activity of glutathione S-transferase by 39 and 61%. The chelated
Cd2+-EDTA complex at these concentrations inhibited the GT activity by 5 and 55%, respectively. 相似文献
17.
Hanana H Talarmin H Pennec JP Droguet M Gobin E Marcorelle P Dorange G 《Cytotechnology》2011,63(3):295-305
Heart cells from the clam Ruditapes decussatus were routinely cultured with a high level of reproducibility in sea water based medium. Three cell types attached to the
plastic after 2 days and could be maintained in vitro for at least 1 month: epithelial-like cells, round cells and fibroblastic
cells. Fibroblastic cells were identified as functional cardiomyocytes due to their spontaneous beating, their ultrastructural
characteristics and their reactivity with antibodies against sarcomeric α-actinin, sarcomeric tropomyosin, myosin and troponin
T-C. Patch clamp measurements allowed the identification of ionic currents characteristic of cardiomyocytes: a delayed potassium
current (I
K slow) strongly suppressed (95%) by tetraethylammonium (1 mM), a fast inactivating potassium current (I
K fast) inhibited (50%) by 4 amino-pyridine at 1 mM and, at a lower level (34%) by TEA, a calcium dependent potassium current (I
KCa) activated by strong depolarization. Three inward voltage activated currents were also characterized in some cardiomyocytes:
L-type calcium current (I
Ca) inhibited by verapamil at 5 × 10−4 M, T-type Ca2+ current, rapidly activated and inactivated, and sodium current (I
Na) observed in only a few cells after strong hyperpolarization. These two currents did not seem to be physiologically essential
in the initiation of the beatings of cardiomyocytes. Potassium currents were partially inhibited by tributyltin (TBT) (1 μM)
but not by okadaic acid (two marine pollutants). DNA synthesis was also demonstrated in few cultured cells using BrdU (bromo-2′-deoxyuridine).
Observed effects of okadaic acid and TBT demonstrated that cultured heart cells from clam Ruditapes decussatus can be used as an experimental model in marine toxicology. 相似文献
18.
Müller F Aschenbach JR Gäbel G 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(4):337-343
This study sought to investigate effects of short-chain fatty acids and CO2 on intracellular pH (pHi) and mechanisms that mediate pHi recovery from intracellular acidification in cultured ruminal epithelial cells of sheep. pHi was studied by spectrofluorometry using the pH-sensitive fluorescent indicator 2′,7′-bis (carboxyethyl)-5(6′)-carboxyfluorescein
acetoxymethyl ester (BCECF/AM). The resting pHi in N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid (HEPES)-buffered solution was 7.37 ± 0.03. In HEPES-buffered solution,
a NH4
+/NH3-prepulse (20 mM) or addition of butyrate (20 mM) led to a rapid intracellular acidification (P < 0.05). Addition of 5-(N-ethyl-N-isopropyl)-amiloride (EIPA; 10 μM) or HOE-694 (200 μM) inhibited pHi recovery from an NH4
+/NH3-induced acid load by 58% and 70%, respectively. pHi recovery from acidification by butyrate was reduced by 62% and 69% in the presence of EIPA (10 μM) and HOE-694 (200 μM),
respectively. Changing from HEPES- (20 mM) to CO2/HCO3
−-buffered (5%/20 mM) solution caused a rapid decrease of pHi (P < 0.01), followed by an effective counter-regulation. 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS; 100 μM) blocked
the pHi recovery by 88%. The results indicate that intracellular acidification by butyrate and CO2 is effectively counter-regulated by an Na+/H+ exchanger and by DIDS-sensitive, HCO3
−-dependent mechanism(s). Considering the large amount of intraruminal weak acids in vivo, both mechanisms are of major importance
for maintaining the pHi homeostasis of ruminal epithelial cells.
Accepted: 8 March 2000 相似文献
19.
Glutathione (γ-glutamylcysteinylglycine, GSH and oxidized glutathione, GSSG), may function as a neuromodulator at the glutamate
receptors and as a neurotransmitter at its own receptors. We studied now the effects of GSH, GSSG, glutathione derivatives
and thiol redox agents on the spontaneous, K+- and glutamate-agonist-evoked releases of [3H]dopamine from mouse striatal slices. The release evoked by 25 mM K+ was inhibited by GSH, S-ethyl-, -propyl-, -butyl- and pentylglutathione and glutathione sulfonate. 5,5′-Dithio-bis-2-nitrobenzoate (DTNB) and l-cystine were also inhibitory, while dithiothreitol (DTT) and l-cysteine enhanced the K+-evoked release. Ten min preperfusion with 50 μM ZnCl2 enhanced the basal unstimulated release but prevented the activation of K+-evoked release by DTT.
Kainate and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) evoked dopamine release but the other glutamate receptor
agonists N-methyl-d-aspartate (NMDA), glycine (1 mM) and trans-1-aminocyclopentane-1,3-dicarboxylate (t-ACPD, 0.5 mM), and the modulators GSH, GSSG, glutathione sulfonate, S-alkyl-derivatives of glutathione, DTNB, cystine, cysteine and DTT (all 1 mM) were without effect. The release evoked by 1 mM
glutamate was enhanced by 1 mM GSH, while GSSG, glutathionesulfonate and S-alkyl derivatives of glutathione were generally without effect or inhibitory. NMDA (1 mM) evoked release only in the presence
of 1 mM GSH but not with GSSG, other peptides or thiol modulators. l-Cysteine (1 mM) enhanced the glutamate-evoked release similarly to GSH. The activation by 1 mM kainate was inhibited by S-ethyl-, -propyl-, and -butylglutathione and the activation by 0.5 mM AMPA was inhibited by S-ethylglutathione but enhanced by GSSG.
Glutathione alone does not directly evoke dopamine release but may inhibit the depolarization-evoked release by preventing
the toxic effects of high glutamate, and by modulating the cysteine–cystine redox state in Ca2+ channels. GSH also seems to enhance the glutamate-agonist-evoked release via both non-NMDA and NMDA receptors. In this action,
the γ-glutamyl and cysteinyl moieties of glutathione are involved. 相似文献
20.
The metabolites produced by Stigmatella WXNXJ-B inhibited the growth of tumor cells. The aims of this research were to evaluate the inhibition potency to different
tumor cell lines and to study the effects of ammonium, phosphate and iron salts on bacterial growth and production of bioactive
metabolites in Stigmatella WXNXJ-B fermentation. The results showed that the chloroform extract (CE-ME) showed the strongest growth inhibition bioactivity
on mouse melanoma cell line (B16), murine colon carcinoma cell line (CT-26), human liver carcinoma cell line (HepG2) and human
breast cancer cell line (MDA-MB231) in vitro and the IC50 values were 9.94, 7.33, 11.34 and 11.66 μg ml−1 respectively. The IC50 value was above 700 μg ml−1 on normal mouse spleen cells. Morphology happened changes in B16 cells treated with CE-ME. The anti-tumor metabolites were
mainly produced during the stationary phase of the bacterial growth. Cell growth was stimulated at the phosphate concentration
below 5 mM, but it was inhibited partly with 10 mM phosphate. The production of bioactive substances was inhibited by the
phosphate. Ammonium increased the cell growth by 250% at 5 mM addition. The inhibition rate to B16 cells was increased to
89% at the concentration of 40 mM ammonium. The bacteria showed the best growth with 4 mM iron. Iron had little effect on
the production at 2 mM, but bigger inhibition effect at higher iron concentration. 相似文献