共查询到20条相似文献,搜索用时 15 毫秒
1.
María M. Elías Elbio J. Comín Marta E. Grosman Susana A. Galeazzi Emilio A. Rodriguez Garay 《生物化学与生物物理学报:生物膜》1982,693(2):265-272
(1) The effects of unconjugated bilirubin on the accumulation of , kinetics of uptake, the efflux of pre-accumulated and water and electrolyte distribution were investigated in the rat kidney cortical slice. (2) The addition of unconjugated bilirubin to the incubation medium decreased the 60 min slice-to-medium concentration ratio of . (3) The decrease in accumulation by unconjugated bilirubin was found to be more pronounced by increasing the concentration of pigment in the medium. (4) The rate of uptake of as a function of concentration differed in aerobiosis and anaerobiosis, and unconjugated bilirubin decreased only the uptake of in aerobic conditions. (5) The efflux of pre-accumulated decreased when unconjugated bilirubin concentration in the medium was low (10–20 μM) but the efflux increased when the concentration of pigment was much higher (100 μM). (6) The addition of unconjugated bilirubin to the medium (40–100 μM) increased intracellular sodium and total tissue water content, and decreased intracellular potassium and oxygen consumption of tissue. However the slices incubated with low concentration of pigment (20 μM) did not exhibit significative changes in cellular functional parameters. (7) These findings suggest that unconjugated bilirubin impairs transport by a complex mechanism that might involve binding of pigment to sites necessary for anion transport, although effects related to pigment toxicity or to its oxidative decomposition are not excluded. 相似文献
2.
This investigation was principally undertaken to test the ionic gradient hypothesis as applied to active uptake in the rabbit kidney cortical slice preparation. Efflux of from the slice was shown to be independent of external Na+ concentration. Transferring slices from a low sodium preincubation to a high sodium incubation medium containing increased intracellular concentrations of both Na+ and K+, and accumulation occurred. Transferring slices from a low sodium preincubation to a high sodium incubation medium containing ouabain and resulted in a net increase in intracellular Na+ concentration but no accumulation occurred. Different combinations of preincubation and incubation media gave a high to low array of intracellular Na+ concentrations and these directly reflected their respective uptake. These results suggest that the Na+-gradient hypothesis does not adequately explain the transport of organic acids in rabbit kidney. These results also suggest that Na+ possibly has an intracellular role through its stimulation of channeled to energizing the accumulative mechanism. 相似文献
3.
(1) In order to assess the possible role of 3′,5′-(cyclic)adenosine monophosphate (cAMP) in the control of glucose transport, the effect of the nucleotide or agents known to increase its intracellular concentration on sugar transport or 45Ca2+ washout were characterized in epididymal fat pads, free fat cells and soleus muscles of the rat. (2) When added to the incubation medium, cAMP (0.1–2.0 mM) stimulated 3-O-[14C]methylglucose washout from fat pads. This effect was abolished by cytochalasin B, and additive to that induced by submaximal (10–25 μU/ml), but not by supramaximal (10 mU/ml) concentrations of insulin. (3) cAMP (2 mM) stimulated the conversion of [U-14C]glucose into CO2 and triacylglycerols. This effect was additive to that of insulin (100 μU/ml). (4) ACTH, glucagon, adrenaline, noradrenaline and salbutamol, which are all known to increase the cAMP content of adipose tissue, stimulated the washout of 3-O-[14C]methylglucose and 45Ca2+ from preloaded fat pads. The fractional losses of the two isotopes were significantly correlated (P < 0.001, r = 0.73). (5) In free fat cells, adrenaline (10−6 M) and salbutamol (10−5 M) stimulated the uptake of 3-O-[14C]methylglucose, and salbutamol (10−5 M) did not interfere with the stimulating effect of insulin (25 μU/ml) on sugar uptake. (6) In rat soleus muscles, adrenaline and salbutamol produced a dose-dependent stimulation of the washout of 3-O-[14C]methylglucose and 45Ca2+. The effect of adrenaline on sugar efflux was abolished by propranolol. (7) It is concluded that the activation of the glucose transport system by insulin is unlikely to be mediated by a drop in the cellular concentration of cAMP. An increase in cAMP brought about by β-adrenoceptor agonists or lipolytic hormones may induce a mobilization of calcium ions from cellular pools into the cytoplasm, which in turn leads to the activation of the glucose transport system demonstrated in the present as well as in several earlier studies. 相似文献
4.
Here we characterized transepithelial taurine transport in monolayers of cultured human intestinal Caco-2 cells by analyzing kinetic apical and basolateral uptake and efflux parameters. Basolateral uptake was Na+- and Cl−- dependent and was inhibited by β-amino acids. Uptake by this membrane showed properties similar to those of the apical TauT system. In both membranes, taurine uptake fitted a model consisting of a non-saturable plus a saturable component, with a higher half-saturation constant and transport capacity at the apical membrane (Km, 17.1 μmol/L; Vmax, 28.4 pmol·cm−2·5 min−1) than in the basolateral domain (Km, 9.46 μmol/L; Vmax, 5.59 pmol·cm−2·5 min−1). The non-saturable influx component, estimated in the absence of Na+ and Cl−, showed no significant differences between apical and basolateral membranes (KD, 89.2 and 114.7 nL·cm−2 · 5 min−1, respectively). Taurine efflux from the cells is a diffusive process, as shown in experiments using preloaded cells and in trans-stimulation studies (apical KD,72.7 and basolateral KD, 50.1 nL·cm−2·5 min−1). Basolateral efflux rates were significantly lower than passive influx rates. We conclude that basolateral taurine uptake in Caco-2 cells is mediated by a transport mechanism that shares some properties with the apical system TauT. Moreover, calculation of unidirectional and transepithelial taurine fluxes reveals that apical influx of this amino acid is higher than basolateral efflux rates, thereby enabling epithelial cells to accumulate taurine against a concentration gradient. 相似文献
5.
Calcium efflux has been studied in barnacle muscle fibres under internal dialysis conditions. Prolonged dialysis of these fibres, with a medium free of ATP and containing 2 mM cyanide and 1 mM iodoacetate, causes the ATP in the perfusion effluent to fall to less than 20 μM. The mean calcium efflux from fibres dialyzed with EGTA buffered solution containing 0.3 μM ionized Ca and no ATP is 0.6 pmol · cm−2 · s−1. A two-fold stimulation of the calcium efflux is observed when ATP is added to fibres previously dialyzed with an ATP-free medium. Withdrawal of Na+ and Ca2+ from the external medium causes a marked drop in the Ca2+ efflux in the presence of internal ATP. 相似文献
6.
Growth of dinoflagellates, Ceratium furca and Ceratium fusus in Sagami Bay, Japan: The role of nutrients 总被引:1,自引:0,他引:1
In order to study the influence of nutrients on the growth characteristics of the dominant dinoflagellates, Ceratium furca and Ceratium fusus, in the temperate coastal area of Sagami Bay, Japan, we conducted field monitoring from January 2000 to December 2005 and performed laboratory culture experiments. In the field study, population densities of C. furca and C. fusus were high, even in low nutrient concentrations (N: 1.58 μM, P: 0.17 μM). Both species were more abundant in the surface and sub-surface layers than in the bottom layers during the stratification periods. In the laboratory study, the specific growth rates of C. furca and C. fusus increased gradually along with increasing nutrients up to the T5 (N: 5 μM, P: 0.5 μM) and T10 (N: 10 μM, P: 1 μM) concentration levels, after which the growth rate plateaued at the T50 (N: 50 μM, P: 5 μM) concentration level. In contrast, the nutrient uptake rates of both species continuously increased, indicating “luxury consumption”, i.e., excessive cellular storage not related to growth rate. The half-saturation constants (Ks) of C. furca for nitrate (0.49 μM) and phosphate (0.05 μM) were slightly higher than C. fusus (0.32 and 0.03 μM, respectively). We offer two reasons why the two Ceratium population densities were maintained at high levels in low nutrient conditions. First, these two species have a competitive advantage over other algal species because of low Ks values and specific characteristics for nutrient uptake such as luxury consumption. Their ability to obtain nutrients through alternative methods, such as phagotrophy, might contribute to bloom formation and population persistence. Second, the cell densities of both Ceratium species increased along with nitrate concentrations in the media even when phosphorus was held constant. In particular, the growth of C. furca was directly supported by various nitrogen sources such as nitrate, ammonium, and urea, although the highest growth rates were observed only in the nitrate-enriched cultures. Our field and laboratory results revealed that the growth rates of the two Ceratium species increased readily in high N:P nutrient conditions (i.e., conditions of P limitation) indicating an advantage over other algal species in phosphorus-limited environments such as Sagami Bay. 相似文献
7.
Two transport systems for glucose were detected: a high affinity system with a Km of 27 μM, and a low affinity system with a Km of 3.3 mM. The high affinity system transported glucose, 2-deoxy-d-glucose (Km = 26 μM), 3-O-methylglucose (Km = 19 μM), d-glucosamine (Km = 652 μM), d-fructose (Km = 2.3 mM) and l-sorbose (Km = 2.2 mM). All sugars were accumulated against concentration gradients. The high affinity system was strongly or completely inhibited by N-ethylmaleimide, quercetin, 2,4-dinitrophenol and sodium azide. The system had a distinct pH optimum (7.4) and optimum temperature (45°C). The low affinity system transported glucose, 2-deoxy-d-glucose (Km = 7.5 mM), and 3-O-methylglucose (Km = 1.5 mM). Accumulation again occurred against a concentration gradient. The low affinity system was inhibited by N-ethylmaleimide, quercetin and 2,4-dinitrophenol, but not by sodium azide. The rate of uptake by the low affinity system was constant over a wide temperature range (30–50°C) and was not much affected by pH; but as the pH of the medium was altered from 4.5 to 8.9 a co-ordinated increase in affinity for 2-deoxy-d-glucose (from 52.1 mM to 0.3 mM) and decrease in maximum velocity (by a factor of five) occurred. Both uptake systems were present in sporelings germinated in media containing sodium acetate as sole carbon source. Only the low affinity system could initially be demonstrated in glucose-grown tissue, although the high affinity system was restored by starvation in glucose-free medium. The half-time for restoration of high affinity activity was 3.5 min and the process was unaffected by cycloheximide. Addition of glucose to an acetate-grown culture inactivated the high affinity system with a half-life of 5–7.5 s. Addition of cycloheximide to an acetate-grown culture caused decay of the high affinity system with a half-life of 80 min. Regulation is thus thought to depend on modulation of protein activity rather than synthesis, and the kinetics of glucose, 2-deoxy-d-glucose and 3-O-methylglucose uptake would be consistent with there being a single carrier showing negative co-operativity. 相似文献
8.
Phenylacetic acid (PAA), a naturally-occurring acidic plant growth substance, was readily taken up by pea (Pisum sativum L. cv. Alderman) stem segments from buffered external solutions by a pH-dependent, non-mediated diffusion. Net uptake from a 0.2 M solution at pH 4.5 proceeded at a constant rate for at least 60 min and, up to approx. 100 M, the rate of uptake was directly proportional to the external concentration of the compound. The net rate of uptake of PAA was not affected by the inclusion of indol-3yl-acetic acid (IAA) in the uptake medium (up to approx. 30 M) and, unlike the net uptake of IAA, was not stimulated by N-1-naphthylphthalamic acid (NPA) or 2,3,5-triiodobenzoic acid. At an external concentration of 0.2 M and pH 4.5, the net rate of uptake of PAA was about twice that of IAA. It was concluded that the uptake of PAA did not involve the participation of carriers and that PAA was not a transported substrate for the carriers involved in the uptake and polar transport of IAA. Nevertheless, the inclusion of 3–100 M unlabelled PAA in the external medium greatly stimulated the uptake by pea stem segments of [1-14C]IAA (external concentration 0.2 M). It was concluded that whilst PAA was not a transported substrate for the NPA-sensitive IAA efflux carrier, it interacted with this carrier to inhibit IAA efflux from cells. Over the concentration range 3–100 M, PAA progressively reduced the stimulatory effect of NPA on IAA uptake, indicating that PAA also inhibited carrier-mediated uptake of IAA. The consequences of these observations for the regulation of polar auxin transport are discussed.Abbreviations IAA
indol-3yl-acetic acid
- DMO
5,5-dimethyloxazolidine-2,4-dione
- NPA
N-1-naphthylphthalamic acid
- PAA
phenylacetic acid
- TIBA
2,3,5-triiodobenzoic acid 相似文献
9.
Isolated rat hepatocytes were used to investigate the uptake of zinc at early exposure times. Hepatocytes were incubated with 65Zn (1–500 μM) and samples were withdrawn at times ranging from 25 s to 60 min. A biphasic pattern of uptake was observed with a rapid first phase of uptake followed by a slower second phase. The relationship between velocity of uptake and substrate concentration for the first phase was nonlinear, while that of the second phase was linear. The presence of 10 μM cadmium produced a decrease in the velocity of uptake of only the first phase. This suggests that the first phase is at least partly carrier mediated, while there is no indication of involvement of a carrier in the second phase. KCN (1 mM) and carbonyl cyanide m-chlorophenylhydrazone (2 μM), did not cause any change in the uptake of 65Zn (1 μM), which suggests that there is no active component in the uptake of zinc. 相似文献
10.
A micropropagation protocol for shoot culture of sweet viburnum (Viburnum odoratissimum) is described. Nodal explants, initially established on MS medium, were transferred to WPM supplemented with combinations of BA and GA3. Maximum shoot multiplication was observed on explants cultured on medium supplemented with BA concentration higher than 1.1 μM, and 14 μM GA3. Although Stage II medium supplemented with BA concentration higher than 1.1 μM resulted in increased shoot multiplication, it also caused a decrease in shoot length. A negative carry over effect of GA3 on rooting was observed in subsequent Stage III cultures. The presence of GA3 in Stage II medium promoted shoot elongation, but it also caused a decrease in microcutting rooting. For this reason, 0.5 μM BA and 14 μM GA3 were selected for optimum Stage II shoot multiplication. Although 100% microcuttings formed roots when cultured on medium containing 6.0 μM NAA, significant callus formation was observed and ex vitro survival rate was low (49%). Rooting was achieved after 3 weeks with 82% of microcuttings on medium supplemented with 3 μM IBA. The survival rate of plantlets under ex vitro conditions was 100% after 3 weeks. Plants looked healthy with no visually detectable phenotypic variation based on observation of about 30 plants. 相似文献
11.
After propagation of Rhizopus javanicus in defined media containing glucose, urea, and mineral salts in deionized distilled water, the ability of the nonliving biomass to sequester cupric ion was assayed. Growth, uptake capacity (saturation uptake at >1 mM Cu2+ concentration in solution), and biosorptive yield (biomass concentration × uptake capacity) were increased by augmentation of the growth medium with mineral salts once growth was under way. In the stationary phase, the uptake capacity of mycelia, which were normally a poor biosorbent, was improved within 4 h of trace metal addition to the growth medium. Growth of the culture was inhibited by excessive concentrations (0.04 to 40 μM) of metals in the medium in the following order: Cu > Co ≥ Ni > Mn > Mo; zinc was not inhibitory at 40 μM, and chromium was stimulatory at 0.53 μM but slightly inhibitory at higher levels. Iron and potassium phosphate stimulated growth at levels of 0.53 and 40 mM, respectively. When R. javanicus was propagated in a medium with a high salt concentration, exponential growth (0.23 h−1) to a biomass concentration of >3 g/liter and a biosorptive yield of >500 μmol/liter was achieved. It is evident that the powerful biosorbent characteristics of Rhizopus biomass led to depletion of available trace minerals in suspension culture, which in turn limited growth. 相似文献
12.
Bioinformatic and Expression Analyses of Genes Mediating Zinc Homeostasis in Nostoc punctiforme
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Lee Hudek L. C. Rai David Freestone Agnes Michalczyk Maria Gibson Y. F. Song M. Leigh Ackland 《Applied microbiology》2009,75(3):784-791
Zinc homeostasis was investigated in Nostoc punctiforme. Cell tolerance to Zn2+ over 14 days showed that ZnCl2 levels above 22 μM significantly reduced cell viability. After 3 days in 22 μM ZnCl2, ca. 12% of the Zn2+ was in an EDTA-resistant component, suggesting an intracellular localization. Zinquin fluorescence was detected within cells exposed to concentrations up to 37 μM relative to 0 μM treatment. Radiolabeled 65Zn showed Zn2+ uptake increased over a 3-day period, while efflux occurred more rapidly within a 3-h time period. Four putative genes involved in Zn2+ uptake and efflux in N. punctiforme were identified: (i) the predicted Co/Zn/Cd cation transporter, putative CDF; (ii) the predicted divalent heavy-metal cation transporter, putative Zip; (iii) the ATPase component and Fe/Zn uptake regulation protein, putative Fur; and (iv) an ABC-type Mn/Zn transport system, putative zinc ZnuC, ZnuABC system component. Quantitative real-time PCR indicated the responsiveness of all four genes to 22 μM ZnCl2 within 3 h, followed by a reduction to below basal levels after 24 h by putative ZIP, ZnuC, and Fur and a reduction to below basal level after 72 h by putative CDF efflux gene. These results demonstrate differential regulation of zinc transporters over time, indicating a role for them in zinc homeostasis in N. punctiforme. 相似文献
13.
Influx, efflux and net uptake of NO
3
–
was studied in Pisum sativum L. cv. Marma in short-term experiments where 13NO
3
–
was used to trace influx. The influx rate in N-limited plants was similar both during net uptake at external concentrations of around 50 M, and at low external NO
3
–
concentrations (4–6 M) when net uptake was practically zero. Efflux could be inferred from discrepancies between influx and net uptake but was never very high in the N-limited plants during net uptake. Close to the threshold concentration for not NO
3
–
uptake, efflux was high and equalled influx. Thus, the threshold concentration can be regarded as a NO
3
–
compensation point. The inclusion of NH
4
+
in the outer medium decreased influx by about 40% but did not significantly affect efflux. The roles of NO
3
–
fluxes and nitrate-reductase activity in regulating/limiting NO
3
–
utilization are discussed.Abbreviations DW
dry weight
- FW
fresh weight
- RN
relative nitrogen addition rate 相似文献
14.
Summary We previously reported that3H-folate uptake by rabbit jejunal brush-border membrane (BBM) vesicles was markedly stimulated by an outwardly directed OH– gradient (pHin 7.7, pHout 5.5), inhibited by anion exchange inhibitors (DIDS, SITS, furosemide), and saturable (folateK
m=0.19 m) suggesting carrier-mediated folate/OH– exchange (or H+/folate cotransport). In the present study, the anion specificity of this transport process was examined. Under conditions of an outwardly directed OH– gradient, DIDS-sensitive folate uptake wascis inhibited (>90%) by reduced folate analogues: dihydrofolate (IC50=0.40 m), folinic acid (IC50=0.50 m), 5-methyltetrahydrofolate (IC50=0.53 m), and (+)amethopterin (IC50=0.93 M). In contrast, 10 m (–)amethopterin had only a modest effect on folate uptake (18% inhibition) suggesting stereospecificity of the folate/OH– exchanger. The nonpteridine compounds which are transported by the folate carrier in L1210 leukemic cells (phthalate, thiamine pyrophosphate, and PO
4
–3
) did not inhibit jejunal folate uptake. Furthermore, folate uptake was not inhibited by SO
4
–2
(4mm) or oxalate (4mm) thereby distinguishing this carrier from the previously described intestinal SO
4
–2
/OH– and oxalate/Cl– exchangers. After BBM vesicles were loaded with3H-folate, the initial velocity of3H-folate efflux was stimulated by unlabeled folate in the efflux medium. The transstimulation of3H-folate efflux by unlabeled folate was furosemide (or DIDS) inhibitable and temperature sensitive. Half-maximal stimulation of furosemide-sensitive3H-folate efflux was observed with 0.25±0.05 m unlabeled folate, a concentration similar to theK
m
for folate uptake. These data suggest that folate-stimulated3H-folate efflux is mediated by the folate/OH– exchanger. With the exception of (–) amethopterin, reduced folate analogues also transstimulated furosemide-sensitive3H-folate efflux in a concentration-dependent manner suggesting stereospecific transport of these analogues by the folate/OH– exchanger. In summary, folate transport by the jejunal folate/OH– exchanger demonstrates bothcis inhibition and transstimulation by reduced folate analogues, but not by other inorganic or organic anions suggesting bidirectional transport of folate and a high degree of anion specificity. 相似文献
15.
A method is described for in vitro propagation of the critically endangered ‘Eneabba mallee’ (Eucalyptus impensa) from southwest Western Australia. Half-strength MS medium supplemented with 0.25 μM 6-benzylaminopurine and 2.5 μM kinetin resulted in the best combination of shoot multiplication and shoot quality compared to other treatments. Shoots of this species tended to be very compact under in vitro conditions. Shoot length was significantly enhanced with the addition of 0.5 or 1.0 μM gibberellic acid (A4 isomer) when compared to basal medium (no hormone supplements) or basal medium containing only cytokinin (0.5 μM zeatin). Up to 97.0 ± 3.0% of shoots produced roots on 1/2 MS medium supplemented with a combination of 5 μM indolebutyric acid and 0.5 μM α-naphthaleneacetic acid. Over 70% of shoots transferred to potting mixture remained viable after 3 months. This study has significantly progressed ex situ conservation initiatives for Eucalyptus impensa. 相似文献
16.
Marie Luise Rao Rao Govind S. Jürgen Eckel Heinz Breuer 《Biochimica et Biophysica Acta (BBA)/General Subjects》1977,500(2):322-332
Isolated rat liver cells take up corticosterone rapidly; the initial rates increase with increasing temperature. A plot of the initial rates against the concentration of corticosterone indicated the presence of saturable and nonsaturable uptake systems. The Eadie-Hofstee plot showed the presence of two saturable and one nonsaturable uptake components. The apparent Kt values of the saturable systems were 64 ± 40 nM (n =3) and 1085 ± 313 nM (n =12). The nonsaturable system, probably diffusion, contributed 12% to the total uptake between 15 and 72 nM corticosterone, the physiological concentration of the free corticosterone in rat serum. Metabolic inhibitors did not influence the uptake of corticosterone. N-Ethylmaleimide, 1-fluor-2,4-dinitrobenzene and sodium ethyl mercurithiosalicylate (1 mM each) decreased the uptake by 40%. Iodoacetate did not have any influence. Treatment of cells with phospholipase A inhibited the uptake 35–45%. In the presence of cortisone, cortisol, dexamethasone, aldosteron, testosterone, estradiol-17β and estrone (2 μM each) the uptake decreased 30–50%. The presence of serum proteins in the external medium inhibits the uptake of corticosterone. These results suggest that corticosterone is transported into the cell and is accumulated. Only the free hormone is available for uptake which in turn may be regulated by protein and lipid components in the plasma membrane of the liver cell. 相似文献
17.
Takaharu Kanno Masanobu Kawanishi Takeji Takamura-Enya Volker M. Arlt David H. Phillips Takashi Yagi 《Mutation Research - Genetic Toxicology and Environmental Mutagenesis》2007,634(1-2):184-191
3-Nitrobenzanthrone (3-nitro-7H-benz[d,e]anthracen-7-one, 3-NBA) is a powerful mutagen and a suspected human carcinogen existing in diesel exhaust and airborne particulates. Recently, one of the major presumed metabolites of 3-NBA, 3-aminobenzanthrone (3-ABA), was detected in human urine samples. Here we analyzed DNA adducts formed in 3-NBA-exposed human hepatoma HepG2 cells by a 32P-postlabeling/thin layer chromatography (TLC) method and a 32P-postlabeling/polyacrylamide gel electrophoresis (PAGE) method. With HepG2 cells exposed to 3-NBA (0.36–36.4 μM) for 3 h, we obtained three spots or bands corresponding to adducted nucleotides. Two were assigned as 2-(2′-deoxyadenosin-N6-yl)-3-aminobenzanthrone-3′-phosphate (dA3′p-N6-C2-ABA) and 2-(2′-deoxyguanosin-N2-yl)-3-aminobenzanthrone-3′-phosphate (dG3′p-N2-C2-ABA), with identical mobilities to those of synthetic standards on PAGE analysis. The chemical structure of the substance corresponding to the other spot or band could not be identified. Quantitative analyses revealed that the major adduct was dA3′p-N6-C2-ABA and its relative adduct labeling (RAL) value at 36.4 μM of 3-NBA was 200.8 ± 86.1/108 nucleotide. 相似文献
18.
The kinetics of glycerol uptake by the perfused rat liver were determined according to a model which includes membrane transport, intracellular phosphorylation and competitive inhibition of glycerol phosphorylation by l-glycerol 3-phosphate. The membrane transport obeys first-order kinetics at concentrations below 10 mM in the affluent medium. The Km of the glycerol phosphorylation was was 10 μM and the Ki of the l-glycerol 3-phosphate inhibition was 50 μM. The maximum activity (V) was 3.70 μmoles/min per g liver wet wt. These results are similar to in vitro kinetics of the glycerol kinase, except that Ki was found to be somewhat lower in the intact organ. At low glycerol concentrations, gradient exists across the liver cell membrane.The increase in the lactate to pyruvate concentration ratio during glycerol metabolism is related to the actual concentration of l-glycerol 3-phosphate, not to the rate of glycerol uptake. 相似文献
19.
Active Transport and Accumulation of Iodide by Newly Isolated Marine Bacteria 总被引:2,自引:1,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Seigo Amachi Yukako Mishima Hirofumi Shinoyama Yasuyuki Muramatsu Takaaki Fujii 《Applied microbiology》2005,71(2):741-745
Iodide (I−)-accumulating bacteria were isolated from marine sediment by an autoradiographic method with radioactive 125I−. When they were grown in a liquid medium containing 0.1 μM iodide, 79 to 89% of the iodide was removed from the medium, and a corresponding amount of iodide was detected in the cells. Phylogenetic analysis based on 16S rRNA gene sequences indicated that iodide-accumulating bacteria were closely related to Flexibacter aggregans NBRC15975 and Arenibacter troitsensis, members of the family Flavobacteriaceae. When one of the strains, strain C-21, was cultured with 0.1 μM iodide, the maximum iodide content and the maximum concentration factor for iodide were 220 ± 3.6 (mean ± standard deviation) pmol of iodide per mg of dry cells and 5.5 × 103, respectively. In the presence of much higher concentrations of iodide (1 μM to 1 mM), increased iodide content but decreased concentration factor for iodide were observed. An iodide transport assay was carried out to monitor the uptake and accumulation of iodide in washed cell suspensions of iodide-accumulating bacteria. The uptake of iodide was observed only in the presence of glucose and showed substrate saturation kinetics, with an apparent affinity constant for transport and a maximum velocity of 0.073 μM and 0.55 pmol min−1 mg of dry cells−1, respectively. The other dominant species of iodine in terrestrial and marine environments, iodate (IO3−), was not transported. 相似文献
20.
Shoot cultures were initiated from mature trees of Alnus glutinosa. On medium containing 1–5 μM 6-benzylamino purine (BAP), the shoots elongated without branching, formed heavy callus at the base of the stems and readily formed roots. The possibility that these characteristics could be attributed to the strong influence of endogenous auxin was tested on media that contained two auxin transport inhibitors, 1-N- naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), at concentrations of 0.1–3 μM, in combination with 2 μM BAP. On these media, shoots produced numerous branches, less callus and no roots. After 30 weeks (five subcultures) on this medium, leaves were smaller and showed signs of vitrification. These problems were resolved without detriment to shoot proliferation, by reverting to medium without NPA or TIBA. Shoots rooted readily after transfer to medium without growth regulators and were successfully acclimatised after transfer to soil. 相似文献