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1.
Structural membrane lipids are known to contribute to the high ethanol resistance of Saccharomyces cerevisiae (2, 4, 17). By manipulating the yeast cellular sterol level by changing the carbon-to-nitrogen source ratio in the chemostat growth medium, high delta 5,7-sterol levels were found to increase the resistance of yeast populations to ethanol-induced death. The resistance of the erg2 (delta 8----delta 7-sterol isomerase) mutant to ethanol-induced death was generally comparable with that of the delta 5,7-sterol-synthesizing strain. In contrast, the sensitivity of anaerobic growth to inhibition by ethanol was higher in the erg2 mutant in comparison with the delta 5,7-sterol-synthesizing strains but a high level of those sterols increased the vulnerability of anaerobic growth to ethanol inhibition. 相似文献
2.
3.
G E Novotny 《Acta anatomica》1984,119(2):106-112
Double-walled coated invaginations ( DWCIs ) of the axolemma, containing oligodendroglial cytoplasm and presumably giving rise to double-walled coated vesicles ( DWCVs ), are observed in the central nervous system (CNS) of adult monkey and mouse. By means of serial sections, DWCIs are clearly distinguishable from the also observable adaxonal invaginations of oligodendroglial cytoplasm. DWCIs range in diameter from 60 to 190 nm with a circular or oval cross section. Their incidence in different regions of the CNS has been determined and evidence is adduced that DWCIs occur randomly along the axolemma. 相似文献
4.
Summary A thermostable NADP-dependent isocitrite dehydrogenase (IDH; EC. 1.1.1.42) was purified from the obligately thermophilic hydrocarbonoclastic bacterium Thermoleophilum minutum YS-4 (ATCC 35265). This was accomplished by affinity chromatography and electroelution from a nondenaturing polyacrylamide gel. The enzyme has an M
r of 60 000 and is composed of two identical subunits of M
r 30 500. The amino acid composition has an Arg/Lys ratio of 4:1 and very high levels of glycine. Under nondenaturing conditions, the enzyme has a distinct difference in electrophoretic mobility relative to IDHs obtained from other genera including the genus Thermus. The secondary strcuture consists of 16% -helix, 20% -sheet, 25% -turn and 37% random coil as determined by circular dichroism spectroscopy. The optimum pH and temperature for activity were 7.2 and 75° C respectively and the apparent K
mvalues for DL-isocitrate adn NADP+ were 33 M, and 48 M, respectively. The enzyme requires divalent cations, such as Mn2+ or Mg2+ for activity. NAD+ cannot substitute for NADP+. Oxaloacetate plus glyoxylate exert considerable inhibition on IDH activity while other glycolytic and tricarboxylic acid cycle intermediates have a lesser effect. p-Chloromercuribenzoic acid was inhibitory to the IDH although isocitrate and Mn2+ offered some protection from this inactivation. The enzyme is thermostable, retaining 84% and 57% of initial activity after incubation for 1 h at 60° and 70° C, respectively. Isocitrate provided protection from thermal inactivation allowing the IDH to maintain 21% activity after 1 h at 80° C.
Offprint requests to: J. J. Perry 相似文献
5.
The effects of Ta-1, a peptide constituent of thymosin fraction 5, were studied on murine autoimmune thyroiditis using two congenic strains of mice, B10.Br (Br) and B10.D2 (D2), which are sensitive and resistant to experimental autoimmune thyroiditis (EAT) induction, respectively. EAT was induced by either 2 weekly iv injections of mouse thyroglobulin with adjuvant lipopolysaccharide (LPS) or intradermal injection of thyroglobulin mixed with complete Freund's adjuvant (CFA). The criteria for induction and intensity of thyroiditis were the level of lymphoid infiltration in the thyroid gland and the titer of anti-thyroglobulin antibodies. Ta-1 was given in 5 or 10 daily sc injections in doses ranging from 0.0001 to 0.1 microgram/injection. The injections were commenced at varying intervals from the 1st to the 4th week after immunization. T-Cell subsets in the spleens were determined 2 weeks after the first antigen injection and thyroid infiltration was determined 3 weeks later. Treatment with Ta-1 between the two antigen injections increased the level of thyroiditis in resistant mice, but had no effect in sensitive mice. Treatment for the first 2 weeks had similar effects in resistant mice, but also suppressed thyroiditis in the sensitive strain. Later treatments, during the 3rd and 4th weeks after immunization also revealed immunomodulating properties of Ta-1, with a suppressing effect on thyroiditis in sensitive mice and an enhancing effect in the resistant strain. Both effects of Ta-1 were dose dependent. The effects of Ta-1 on the individual phenotypes were also dose dependent. The dose of 0.01 microgram greatly lowered the percentages of Lyt-2+3+ cells in D2 mice and mildly increased the percentages in Br mice, but did not change the Lyt-1+ cell level in either strain. On the other hand, the dose of 0.001 microgram greatly increased the percentage of Lyt-1+ cells in D2 mice and mildly decreased it in the Br strain, but did not alter the Lyt-2+3+ cell subset in either strain. Thus, both doses of Ta-1 modulated Lyt-1+/2+3+ ratios, with each dose affecting a different T-cell subset. The changes in the response to thyroglobulin are apparently exerted through the regulation of the functional T-cell subset balance. 相似文献
6.
H. Christopher Wilson Nadine C. Milos 《In vitro cellular & developmental biology. Plant》1987,23(5):323-331
Summary This study investigates the nutritional requirements ofXenopus laevis neural crest cells and melanophores developing in vitro. A comparison is made between the growth and differentiation of cells
in serum-containing medium and a chemically defined, serum-free medium that we have designed. Our chemically defined medium
is more efficient than serum-supplemented medium in promoting proliferation of these cells. Several supplements are required
to enhance culture development. These include insulin, α-melanocyte stimulating hormone, somatotropin, luteotrophic hormone,
linoleic acid, uridine, and putrescine. In addition, collagen and fibronectin provide the most conductive environment tested
for cell migration and adhesion.
This work was supported by establishment and major equipment grants from the Alberta Heritage Foundation for Medical Research
to N. C. M. Nadine C. Milos is a Heritage Medical Research Scholar of the Alberta Heritage Foundation for Medical Research. 相似文献
7.
Mechanism of inducer expulsion in Streptococcus pyogenes: a two-step process activated by ATP. 总被引:22,自引:13,他引:9 下载免费PDF全文
The mechanism of methyl-beta-D-thiogalactoside-phosphate (TMG-P) expulsion from Streptococcus pyogenes was studied. The expulsion elicited by glucose was not due to exchange vectorial transphosphorylation between the expelled TMG and the incoming glucose since more beta-galactoside was displaced than glucose taken up, and the stoichiometry between TMG and glucose transport was inconstant. Instead, two distinct and sequential reactions, intracellular dephosphorylation of TMG-P followed by efflux of free TMG, mediated the expulsion. This was shown by temporary accumulation of free TMG effected by competitive inhibition of its efflux and by the aid of arsenate, which arrested dephosphorylation of TMG-P but did not affect efflux of free TMG formed intracellularly before arsenate addition. The competitive inhibition of TMG efflux by its structural analogs suggests that a transport protein facilitates the expulsion. Iodoacetate or fluoride prevented TMG-P dephosphorylation and its expulsion. However, provision of ATP via the arginine deiminase pathway restored these activities in the presence of the glycolytic inhibitors and stimulated expulsion in their absence. Other amino acids tested did not promote this restoration, and canavanine or norvaline severely inhibited it. Arginine without glucose neither elicited the dephosphorylation nor evoked the expulsion of TMG-P. Ionophores or ATPase inhibitors did not prevent the expulsion as elicited by glucose or its restoration by arginine. The results suggest that activation of the dephosphorylation-expulsion mechanism occurs independently of a functional glycolytic pathway, requires ATP provision, and is possibly due to protein phosphorylation controlled by a yet unknown metabolite. The in vivo phosphorylation of a protein (approximate molecular weight - 10,000) under the conditions of expulsion was demonstrated. 相似文献
8.
9.
Djordje Boskov Mirjana Jocic Ksenija Jovanovic Milos Ljubisavljevic Radmila Anastasijevic 《Biological cybernetics》1994,71(4):341-348
Spike discharges of skeletomotor neurons innervating triceps surae muscles elicited by white noise modulated transmembrane
current stimulation and muscle stretch were studied in decerebrated cats. The white noise modulated current intensity ranged
from 4.3 to 63.2 nA peak-to-peak, while muscle stretches ranged from 100 μm to 4.26 mm peak-to-peak. The neuronal responses
were studied by averaging the muscle length records centered at the skeletomotor action potentials (peri-spike average, PSA)
and by Wiener analysis. Skeletomotor spikes appeared after a sharp peak in PSA of the injected current, preceded by a longer-lasting
smaller wavelet of either depolarizing or hyperpolarizing direction. The PSA amplitude was not related to the injected current
amplitude nor showed any differences related to the motor unit type. The PSA amplitudes were virtually independent of the
stretching amplitude σ, after an initial increase with stretching amplitudes in the range of 15–40 μm (S.D.), or 100–270 μm
peak-to-peak.Analyses of cross-spectra indicated a small or absent increase in gain with frequency in response to injected
current, but about 20 dB/decade in the range 10–100 Hz in response to muscle stretch. The peaks of both Wiener kernels in
response to current injection appear to decrease with the amplitude of injected current, but this decrease was not statistically
significant. The narrow first-order kernels suggest that the transfer function between the current input and spike discharge
is lowpass with a wide passband, i.e. there is very little change in dynamics. The values of the second-order kernels appear
to be nonzero only along the main diagonal. This is characteristic of a simple Hammerstein type cascade, i.e. a zero memory
nonlinearity followed by a linear system. Small values of second-order kernels away from the origin and narrow first-order
kernels suggest that the linear cascade contributes very little to the overall dynamic response.In contrast to Wiener kernels
found in response to current injection, the Wiener kernels in response to stretch showed a decreasing trend with stretch amplitude.
The size of the second-order kernels decreased to a somewhat larger extent with input amplitude than that of the first-order
kernels, indicating an amplitude-dependent nonlinearity. Overall, the transformation between length and spike output was described
as an LNNL cascade with second-order nonlinearities.
Received: 1 April 1993/Accepted in revised form: 24 March 1994 相似文献
10.