共查询到20条相似文献,搜索用时 15 毫秒
1.
A new technique is described for measuring the adhesive strength of a gingival cell line to an agar substratum by the modification of the original "blister" test for adhesives. A cell monolayer was developed on a Petri dish with a hole in the center of the growing surface, overlayed with agar, and the system pressurized to debond the cells from the agar surface. Pressure changes were measured by a capacitance pressure transducer the output of which was measured by a strip-chart recorder. The modulus (E) of the agar overlay was determined and used in the calculation of the adhesive-bond strength (gammaalpha). The gammaalpha yield for the gingival cell line (cell-agar debond) was 48.8 ergs per cm2, and for the control (no cells) (agar-polystyrene debond) was 30.0 ergs per cm2. 相似文献
2.
John L. Stephenson 《Bulletin of mathematical biology》1960,22(1):1-17
The conditions under which the output,γ
b
(t), of a biological system is related to the input,γ
a
(t), by an integral equation of the typeγ
b
(t) = ∫
0
t
γ
a
(ω)w(t−ω)dω, where ω(t) is a transport functioncharacteristic of the system, are analyzed in detail. Methods of solving this type of integral equation are briefly discussed. The theory
is then applied to problems in tracer kinetics in which input and output are sums of exponentials, and explicit formulae,
which are applicable whether or not the pool is uniformly mixed, are derived for “turnover time” and “pool” size. 相似文献
3.
Aguedo M Gomes N Garcia EE Waché Y Mota M Teixeira JA Belo I 《Biotechnology letters》2005,27(20):1617-1621
Yarrowia lipolytica converts methyl ricinoleate to γ-decalactone, a high-value fruity aroma compound. The highest amount of 3-hydroxy-γ-decalactone
produced by the yeast (263 mg l-1) occurred by increasing the kLa up to 120 h−1 at atmospheric pressure; above it, its concentration decreased, suggesting a predominance of the activity of 3-hydroxyacyl-CoA
dehydrogenase. Cultures were grown under high-pressure, i.e., under increased O2 solubility, but, although growth was accelerated, γ-decalactone production decreased. However, by applying 0.5 MPa during
growth and biotransformation gave increased concentrations of dec−2-en-4-olide and dec-3-en-4-olide (70 mg l−1). 相似文献
4.
T cell clones (CD4+CD8–TCRαβ+γδ–) derived from bone marrow transplant recipients were stimulated with phytohaemagglutinin (PHA) +interleukin-2 (IL-2) in the
presence of irradiated (50 Gy) peripheral blood mononuclear cells (PBMC) derived from acute leukaemia patients(leukaemic PBMC
containing more than 95% blast cells). Leukaemic PBMC could function as accessory cells during mitogenic T cell activation
resulting in both T cell proliferation and a broad T cell cytokine response [IL-3, IL-4, IL-10, granulocyte/macrophage-colony-stimulating
factor (GM-CSF) tumour necrosis factor α (TNFα) and interferon γ (IFNγ) secretion]. Blockade of IL-1 effects by adding IL-1
receptor antagonist together with PHA+IL-2+leukaemia blasts increased T cell proliferation, whereas IL-6-neutralizing antibodies
did not alter T cell proliferation. A qualitatively similar T cell cytokine response and a similar cytokine profile (highest
levels detected for GM-CSF and IFNγ) were detected when normal polyclonal T cell lines were stimulated with PHA in the presence
of non-irradiated leukaemic PBMC. When leukaemic PBMC derived from 18 acute myelogenous leukaemia patients were cultured with
PHA and cells from a polyclonal T cell line, increased concentrations of the T cell cytokines IFNγ and IL-4 were detected
for all patients. We conclude that T cell activation resulting in proliferation and a broad cytokine response can take place
in the presence of excess acute myelogenous leukaemia blasts.
Received: 30 November 1995 / Accepted: 9 January 1996 相似文献
5.
Acid-base properties of wheat, lupin, pea root cell walls were investigated. The roots of etiolated and green plants of different
age were analysed by the potentiometric method. The ion exchange capacity of root cell walls (Si) was estimated at various pH values (pHi 2 to pHi 12) and constant ion strength of the solution (10 mM). To analyse polysigmoid curves pHi =f (Si), Gregor's equation was used. It was shown that Gregor's model fits fairly well the experimental data. The total quantities
of cation-exchange (St
cat) and anion-exchange (St
an) groups were determined in the root cell walls. It was shown that the quantity of anion exchange groups is varied through
a small range (60–185 μmol/g dry wt.) in plant species tested, and that the St
cat differs widely from 550 to 1300 μmol/g dry wt. For leguininous plants the quantity of acidic groups (fixed anions) is nearly
twice as large as that for cereals. It was found that in seedlings as well as in plants, there are 3 cation-exchange groups
and one anion-exchange group in root cell walls. The quantity of functional groups of each type (Sj) was estimated, and the corresponding values of nj and pKa
j were calculated. It can be assumed that the groups with the pKa
1 ≈ 3.2 are amine groups, the ones with PKa
2 ≈ 5 are groups of galacturonic acid, the ones with pKa ≈ 7.5 are the carboxyl groups of the second species, and the ones with pKa
4 ≈ 40 are the phenolic groups. The values of dissociation constants (pKa
j) and Sj indicate that the root cell walls of wheat, lupin and pea are identical in qualitative structure of ionogenic groups but
vary in the quantity of each ionogenic group. It was demonstrated that the summarized quantity of carboxyl groups (S2 + S3) should be connected directly with the pH gradient in the extracellar space at the membrane surface. The gradient arises
from ion-exchange reactions between cations of an outer medium and protons of the ionized carboxyl groups of the cell walls.
The results suggest that, St
cat and St
an allow the quantitative estimation of ion exchange properties of the cell walls. The resulting parameters (Sj, pKa
j and nj) allow prediction of changes in an ionic composition of a medium that bathes the cell membrane, during the first step of
mineral nutrition uptake.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
Javier Orduña-Rojas Karla Y. García-Camacho Priscila Orozco-Meyer Rafael Ríosmena-Rodríguez Isaí Pacheco-Ruiz José A. Zertuche-González Alf E. Meling-López 《Journal of applied phycology》2008,20(2):169-175
Agar properties of two potentially commercial important seaweeds from the Gulf of California were studied. Maximum yield in
Gracilaria vermiculophylla (45.7%) occurred during the summer months, coinciding with high water temperatures (31°C) whereas minimum yields (11.6%)
were obtained during the coldest months of the year when populations of this species diminish in the bay. Gracilariopsis longissima showed two yield peaks, one in spring and another in fall, before the maximum and minimum seawater temperatures. Gel strength
in native agar from the two species was low (<22.5 g cm−2) for most of the year. G. vermiculophylla native agar showed a slight increase in gel strength from June to August, which were the hottest months. Maximum value was
85 g cm−1 in August. Maximum gel strength in G. longissima was observed in October (91 g cm−1), and an unusual native agar with no detectable gel strength was observed in March and April samples. Gelling temperatures
range from 27.7 to 36.5°C in G. vermiculophyla and from 26.6 to 34.9°C in G. longissima, meanwhile melting points were 73.9 – 53.5°C and 75.5 – 56.6°C, respectively. Sulfate content was high, 6.3–13.9% in G. vermiculophylla and 1.9–11.9% in G. longissima, and on the other hand 3,6 anhydrogalactose content was low 12.1–26.7% and 9.1–23%, respectively compared to other species.
Results obtained showed that mean native agar yields of Gracilaria vermiculophylla and Gracilariopsis longissima from the Gulf of California are comparable to other tropical Gracilaria. However, the low gel strength, high sulfate content and low 3,6 anhydrogalactose content observed in the native agar extracted
from these species make this an agaroid, thus alternative methods of extraction should be used to evaluate the possibility
of commercial utilization of both species. 相似文献
7.
Summary The intact human reabsorptive sweat duct (RD) has been a reliable model for investigations of the functional role of “endogenous”
CFTR (cystic fibrosis transmembrane conductance regulator) in normal and abnormal electrolyte absorptive function. But to
overcome the limitations imposed by the use of fresh, intact tissue, we transformed cultured RD cells using the chimeric virus
Ad5/SV40 1613 ori-. The resultant cell line, RD2(NL), has remained differentiated forming a polarized epithelium that expressed
two fundamental components of absorption, a cAMP activated Cl− conductance (Gcl) and an amiloride-sensitive Na+ conductance (GNa). In the unstimulated state, there was a low level of transport activity; however, addition of forskolin (10−5
M) significantly increased the Cl− diffusion potential (Vt) generated by a luminally directed Cl− gradient from − 15.3 ± 0.7 mV to −23.9 ± 1.1 mV,n=39; and decreased the transepithelial resistance (Rt) from 814.8 ± 56.3 Ω.cm2 to 750.5 ± 47.5 Ω.cm2,n=39, (n=number of cultures). cAMP activation, anion selectivity (Cl−>I−>gluconate), and a dependence upon metabolic energy (metabolic poisoning inhibited GCl), all indicate that the GCl expressed in RD2(NL) is in fact CFTR-GCl. The presence of an apical amiloride-sensitive GNa was shown by the amiloride (10−5
M) inhibition of GNa as indicated by a reduction of Vt and equivalent short circuit current by 78.0 ± 3.1% and 77.9 ± 2.6%, respectively, and an increase in Rt by 7.2 ± 0.8%,n=36. In conclusion, the RD2(NL) cell line presents the first model system in which CFTR-GCl is expressed in a purely absorptive tissue. It provides an opportunity to study the properties and role of CFTR in the context
of absorptive function in immortalized epithelial cells. 相似文献
8.
Alkaline stable (pH 7.75–12.5) urease from Sporosarcina ureae was purified over 400-fold by ion exchange and hydrophobic interaction chromatography. The cytoplasmic enzyme was remarkably
active with a specific activity of greater than 9300 μmol urea degraded min-1 mg protein-1 at pH 7.5, where it has optimal activity. Although S. ureae is closely related to Bacillus pasteurii, known to posses a homopolymeric urease containing 1 nickel per subunit [M
r=65000], the S. ureae enzyme is comprised of three subunits [apparent M
r=63100 (α), 14500 (β), and 8500 (γ)] in an estimated ∝βγ stoichiometry and contains 2.1±0.6 nickel ions per ∝βγ unit as measured
by atomic absorption spectrometry. Stationary phase cultures sometimes possessed low levels of urease activity, but the specific
activity of cell extracts of partially purified urease preparations from such cultures could be elevated by heat treatment,
dilution, or dialysis to values comparable to those observed in samples from exponentially grown cells. 相似文献
9.
Mamoru Harada Koji Tamada Koichiro Abe Tieli Li Yasuhiro Onoe Hitoshi Tada Katsunori Tatsugami Takashi Ando Genki Kimura Kikuo Nomoto 《Cancer immunology, immunotherapy : CII》1998,47(4):198-204
A B16 melanoma-specific CD8+ T cell line (AB1) was established from the spleen cells of C57BL/6 mice cured of B16 melanoma with interleukin (IL)-12 treatment.
The AB1 line exclusively used T cell receptor Vβ11. The AB1 cells exhibited a cytolytic activity against both syngeneic B16 melanoma and allogeneic P815 mastocytoma, whereas
a cold inhibition assay revealed specificity of the AB1 cells against B16 melanoma. Their lostability to kill a class I loss
variant of B16 melanoma was restored by the transfection of H-2Kb gene. In addition, their interferon (IFN)-γ production was significantly suppressed by the addition of anti-H-2Kb monoclonal antibody, and RT-PCR analysis showed that the AB1 line expressed the mRNA encoding IFN-γ, but not IL-4 or IL-10.
The experiment using synthetic peptides of tyrosinase-related protein-2 (TRP-2) revealed that the AB1 cells could recognize
TRP-2181–188 peptide. Moreover, the AB1 cells showed an in vivo antitumor effect against established pulmonary metastases of B16 melanoma.
Overall, these results indicate that the Tc1-type Vβ11
+ AB1 cells exert an antitumor activity against syngeneic B16 melanoma through recognition of TRP-2181–188 peptide in an H-2Kb-restricted manner.
Received: 4 June 1998 / Accepted: 21 July 1998 相似文献
10.
Tze Kinip Pierre M. Galletti Patrick Aebischer 《In vitro cellular & developmental biology. Plant》1990,26(2):162-168
Summary The growth and differentiation of an established renal epithelial cell line, LLC-PK1, on membrane bound mussel adhesive protein (MAP), collagen, and extracellular matrix (ECM) in serum-containing medium was
studied. Cell attachment and growth on uncoated- vs. protein-coated cellulose nitrate and acetate membranes did not differ
significantly, and confluence was achieved on all membranes. However, cells remained in a single monolayer only when plated
on collagen or ECM. LLC-PK1 monolayers grown on ECM-coated membranes displayed the highest transepitheliald-glucose transport (333 ± 22 ng·cm−2·min−1) whereas cells plated on collagen-coated membranes displayed the lowest (94 ± 23 ng·cm−2·min−1). Glucose flux values increased with age of the culture, reaching a plateau at 28 d postseeding. These results indicate that
the underlying substratum and cell age can affect differentiation of renal epithelial cells in vitro. 相似文献
11.
A method for plant regeneration in Robinia pseudoacacia L. from cell suspension culture was established. Non regenerative friable callus from hypocotyls and cotyledon explants from
in vitro raised seedling induced on solid Murashige and Skoog (MS) medium supplemented with 0.05 mg dm−3 2,4-dichlorophenoxyacetic acid (2,4-D) was used for initiation of cell suspension cultures on same MS medium but without
agar. Single cells were isolated after 3 d and the optimum cell density was 1–3 × 104 cells per cm3 of the liquid MS medium. Plating efficiency was 29.6 % and callus formed within 4 weeks was subcultured and transferred to
solid MS medium supplemented with 0.6 mg dm−3 benzyladenine (BA) along with 0.05 mg dm−3 α-naphthalene-1-acetic acid (NAA) for the induction of adventitious bud primordia. The shoots developed were isolated and
re-cultured on MS medium containing 0.6 mg dm−3 BA. These microshoots after dipping in 1–2 cm3 of 10 mg dm−3 indole-3-butyric acid (IBA) for 24 h in dark were cultured on half strength solid MS medium supplemented with 0.05 % charcoal
and showed 80–82 % rooting within 4 weeks. 相似文献
12.
Journal of Plankton Research, 11, 12731295, 1989. The values of P/U0 (Table I) and fluid velocity used to calculatethe energy required for sieving (pp. 12891290) and severalequations (footnote b of Table I; p. 1290, lines 34)are incorrect. The corrected table appears below: Table I. Filter setule measurements (mean and within specimenstandard deviation) of the gnathobases for the cladocerans studiedaGnathobaseof trunklimb number. bP = 8µU0/(b(1 21nt + 1/6(t2) - 1/144(t4))), whereP = pressure drop in dyn cm2, =3.1416, U0 = fluid velocityin cm s1, b = distance between setule centres in cm,t = ( x setule diameter)/b and µ = 0.0101 dyn s1cm2. Formula from Jørgensen (1983). The text (p. 1289, line 19 to p. 1290, line 10) should read: organism. Using a similar argument, a 0.5 mm Ceriodaphnia witha filter area of 0.025 mm2 (Ganf and Shiel, 1985) and pressuredrop P = 2757 dyn cm2 (with fluid velocity of 0.07 cms1) allocates only 2171 ergs h1 to filtrationof a total energy expenditure of 104 ergs h1 [filtrationenergy (ergs h1) = area (cm2) x pressure drop (dyn cm2)x 3600 (s h1) x 1/0.2 (efficiency of conversion of biochemicalinto mechanical work); total energy (ergs h1) = respiration(0.05 µl O2 ind1 h1 consumed; Gophen, 1976)x conversion factor (2 x 105 ergs µl1 O2). Withan estimated 0.034 mm2 in filter area, fluid velocity of 0.041cm s1 and respiration of 1.8 x 104 ergs h1 (calculatedfrom Porter and McDonough, 1984), a 0.5 mm Bosmina uses <4%of its metabolism to overcome filter resistance. The velocities used in the original examples (0.4 cm s1for Ceriodaphnia, 0.2 cm s1 for Bosmina) were derivedfrom literature values of appendage beat rate and estimatesof the distance travelled by the appendages during each beatcycle. This approach unnecessarily assumes that all water movedpasses through the filter. In the new calculations, the flowacross the filter needed for food to be collected by sieving(0.07 cm s1 for Ceriodaphnia and 0.041 cm s1 forBosmina) was determined from the maximum clearance rate/filterarea. The amended energy expenditures, although higher, do notrefute the sieve model of particle collection. 相似文献
13.
Peroxisome proliferator-activated receptor gamma (PPARγ) activation by its ligands reportedly inhibits monocyte function.
However, because the concentrations of PPARγ ligands used in previous studies were higher than typically expected to activate
PPARγ, we clarified whether PPARγ ligands influence monocyte function and cell viability of the human monocyte cell line THP-1.
We determined tumor necrosis factor-alpha (TNF-α) release as a monocyte function and cell viability using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium
bromide. Both troglitazone and 15-deoxy-Δ12,14-prostaglandin J2 (15-d-PGJ2) seemed to inhibit phorbol ester-induced TNF-α release from THP-1 cells. On the other hand, neither pioglitazone
nor rosiglitazone inhibited phorbol ester-induced TNF-α release. Because the cytotoxicity of troglitazone and 15-d-PGJ2 was
significantly (p<0.05, Tukey–Kramer) stronger than that of pioglitazone and rosiglitazone, the inhibition of TNF-α release seemed to parallel
the lack of cell viability. We concluded that PPARγ ligands did not directly inhibit TNF-α release in THP-1 cells.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Ko-ichiro Miyamoto Parida Yamada Ryo-taro Yamaguchi Takami Muto Ayumi Hirano Yasuo Kimura Michio Niwano Hiroko Isoda 《Cytotechnology》2007,55(2-3):143-149
In this study, we report on an in situ monitoring system of living cultured cells using infrared absorption spectroscopy in
the geometry of multiple internal reflections (MIR-IRAS). In order to observe living cultured cells, the temperature in the
sample chamber of a FT-IR spectrometer was maintained at 37 °C and a humidified gas mixture containing 5% CO2 was introduced into the sample chamber. Human breast cell line MCF-7 cultured on Si MIR prisms were placed in the sample
chamber and infrared spectra of MCF-7 cells were collected for 5 h. It was found that the adhesion and metabolism of MCF-7
cells could be monitored by the absorption intensity of amide-II protein band (1,545 cm−1) and also by the absorption intensities of CH
x
bands (2,700–3,100 cm−1). These results suggest that our system is useful for a nondestructive and non-label monitoring of cell viability. Our method
based on infrared absorption spectroscopy has a potential for bioscreening application. 相似文献
15.
The effects of nutrient enrichment on the release of dissolved organic carbon and nitrogen (DOC and DON, respectively) from
the coral Montipora digitata were investigated in the laboratory. Nitrate (NO3
−) and phosphate (PO4
3−) were supplied to the aquarium to get the final concentrations of 10 and 0.5 μmol l−1, respectively, and the corals were incubated for 8 days. The release rate of DON per unit coral surface area significantly
decreased after the nutrient enrichment, while the release rate of DOC was constant. Because the chlorophyll a (chl a) content of zooxanthellae per unit surface area increased, the release rate of DOC significantly decreased when normalized
to unit chl a. These results suggested that the incorporation of NO3
− and PO4
3− stimulated the synthesis of new cellular components in the coral colonies and consequently, reduced extracellular release
of DOC and DON. Actually, significant increase in N and P contents relative to C content was observed in the coral’s tissue
after the nutrient enrichment. The present study has concluded that inorganic nutrient enrichment not only affects coral-algal
metabolism inside the colony but also affects a microbial community around the coral because the organic matter released from
corals functions as energy carrier in the coral reef ecosystem. 相似文献
16.
Miki Watanabe Sulaiman Sheriff Theresa A. Ramelot Nijiati Kadeer Junho Cho Kenneth B. Lewis Ambikaipakan Balasubramaniam Michael A. Kennedy 《International journal of peptide research and therapeutics》2011,17(4):281-299
After severe burn injury, proinflammatory cytokine levels are elevated in serum and skeletal muscle, which in turn increases
protein breakdown and decreases protein synthesis. In this study, C2C12 mouse skeletal muscle cell line myotubes were exposed
to proinflammatory cytokines tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) as an in vitro cell-line model of catabolic
response to burn injury and then treated with des-acyl ghrelin (DAG), a 28 amino acid polypeptide hormone thought to inhibit
protein breakdown and increase protein synthesis, to assess its therapeutic potential. Nuclear magnetic resonance-based metabonomics
was used to monitor metabolic activity of C2C12 myotubes under four treatment conditions: (1) control, (2) TNF-α/IFN-γ (TI),
(3) DAG (DA), and (4) TNF-α/IFN-γ followed by DAG (TIDA) to assess the effect of DAG treatment on cellular metabolic response
during basal or catabolic conditions. Twelve metabolites showed significant changes in concentrations following treatments
in the hydrophilic cell extracts. Lactate (P < 10−4) and citrulline (P < 10−9) increased with TNF-α/IFN-γ treatment, indicating increased protein degradation, and returned to control levels in the TIDA
group. Adenosine nucleotide levels had decreased trends in TI myotubes that returned to baseline levels after DAG treatment
(P < 10−4). Guanidinoacetate and pantothenate, metabolites involved in protein synthesis and cell proliferation, had increased concentration
trends following DAG treatment in both the DA and TIDA groups. Our metabonomics analysis provides further evidence that DAG
counteracts the catabolic response caused by elevated muscle TNF-α/IFN-γ cytokine levels following severe burns and can play
a potential therapeutic role in treatment of burn injury. 相似文献
17.
Inhibition of cell division by blue light 总被引:2,自引:0,他引:2
Microsporocytes of Lilium and Trillium can revert into a mitotic cycle when separated from the anther before the beginning of meiosis and cultured in vitro. Repeated short daily irradiations with visible blue light (106 ergs cm−2 sec−1) inhibit the onset of mitosis; the cells remain in interphase instead. The inhibition of cell division is reversed after the end of the light treatment. Meiosis is not affected by light. Part of the premeiotic G2 phase is light sensitive. No arrest of DNA-, RNA- or protein synthesis is involved in the photoinhibition of onset of mitosis. Irradiation with blue light decreases the α- absorption band of cytochrome a3 but not of cytochrome a. This effect on cytochrome oxidase, however, is observed in all stages of meitotic prophase as well as in G2 cells. 相似文献
18.
Other than the fact that the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel can be activated by cAMP dependent kinase (PKA), little is known about the signal transduction pathways regulating
CFTR. Since G-proteins play a principal role in signal transduction regulating several ion channels [4, 5, 9], we sought to
test whether G-proteins control CFTR Cl− conductance (CFTR G
Cl
) in the native sweat duct (SD). We permeabilized the basolateral membrane with α-toxin so as to manipulate cytosolic nucleotides.
We activated G-proteins and monitored CFTR G
Cl
activity as described earlier [20, 23, 25]. We now show that activating G-proteins with GTP-γ-S (100 μm) also activates CFTR G
Cl
in the presence of 5 mm ATP alone (without exogenous cAMP). GTP-γ-S increased CFTR G
Cl
by 44 ± 20 mS/cm2 (mean ±se; n= 7). GDP (10 mm) inhibited G-protein activation of CFTR G
Cl
even in the presence of GTP-γ-S. The heterotrimeric G-protein activator (AlF4
−) in the cytoplasmic bath activated CFTR G
Cl
(increased by 51.5 ± 9.4 mS/cm2 in the presence of 5 mm ATP without cAMP, n= 6), the magnitude of which was similar to that induced by GTP-γ-S. Employing immunocytochemical-labeling techniques, we
localized Gαs, Gαi, Gαq, and Gβ at the apical membranes of the sweat duct. Further, we showed that the mutant CFTR G
Cl
in ducts from cystic fibrosis (CF) subjects could be partially activated by G-proteins. The magnitude of mutant CFTR G
Cl
activation by G-proteins was smaller as compared to non-CF ducts but comparable to that induced by cAMP in CF ducts. We conclude
that heterotrimeric G-proteins are present in the apical membrane of the native human sweat duct which may help regulate salt
absorption by controlling CFTR G
Cl
activity.
Received: 9 June 2000/Revised: 5 October 2000 相似文献
19.
Viable Saccharomyces cerevisiae and Candida shehatae cells were co-immobilized in a composite agar layer/microporous membrane structure. This immobilized-cell structure was placed
in a vertical position between the two halves of a double-chambered, stainless-steel bioreactor of original design and applied
to the continuous alcoholic fermentation of a mixture of glucose (35 g dm−3) and xylose (15 g dm−3). Various dilution rates and initial cell loadings of the gel layer were tested. Simultaneous consumption of the two sugars
was always observed. The best fermentation performance was obtained at low dilution rate (0.02 h−1) with an excess of C. shehatae over S. cerevisiae in the initial cell loading of the gel (5.0 mg dry weight and 0.65 mg dry weight cm−3 gel respectively): 100% of glucose and 73% of xylose were consumed with an ethanol yield coefficient of 0.48 g g total sugars−1. In these conditions, however, the ethanol production rate per unit volume of gel remained low (0.37 g h−1 dm−3). Viable cell counts in gel samples after incubation highlighted significant heterogeneities in the spatial distribution
of the two yeast species in both the vertical and the transverse directions. In particular, the overall cell number decreased
from the bottom to the top of the agar sheet, which may explain the low ethanol productivity relative to the total gel volume.
Received: 26 February 1998 / Received revision: 15 April 1998 / Accepted: 19 April 1998 相似文献
20.
Single-channel properties of a delayed rectifier voltage-gated K+ channel (I-type) were investigated in peripheral myelinated axons from Xenopus laevis. Channels activated between −60 and −40 mV with a potential of half-maximal activation, E50, at −47.5 mV. Averaged single-channel currents activated with a time delay at all membrane potentials tested. Time to half-maximal
activation decreased from 80 to 1.6 msec between −60 and +40 mV. The channel inactivated monoexponentially with a time constant
of 10.9 sec at −40 mV. The time constant of deactivation was 126 msec at −80 mV and 16.9 msec at −110 mV. In symmetrical 105
mm K+, the single-channel conductance (γ) was 22 and 13 pS at negative and positive membrane potentials, respectively, at 13–15°C.
In Na+-rich solution with 2.5 mm extracellular K+γ was 7 pS and the reversal potential was negative to −80 mV, indicating a high selectivity for K+ over Na+. γ depended on extracellular K+ concentration (K
D
= 19.6 mm) and temperature (Q
10= 1.45). External tetraethylammonium (TEA) reduced the apparent single-channel current amplitude at all potentials tested
with a half-maximal inhibiting concentration (IC50) of 0.6 mm. Open probability of the channel, but not single-channel current amplitude was decreased by extracellular dendrotoxin (DTX,
IC50= 6.8 nm) and mast cell degranulating peptide (MCDP, IC50= 41.9 nm). In Ringer solution the membrane potential of macroscopic I-channel patches was about −65 mV and depolarized under TEA and
DTX. It is concluded that besides their activation during action potentials, I-channels may also stabilize the resting membrane
potential.
Received: 2 June 1995/Revised: 13 October 1995 相似文献