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171.
Polysaccharide Fraction from Higher Plants which Strongly Interacts with the Cytosolic Phosphorylase Isozyme : I. Isolation and Characterization 总被引:2,自引:1,他引:1
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From leaves of Spinacia oleracea L. or from Pisum sativum L. and from cotyledons of germinating pea seeds a high molecular weight polysaccharide fraction was isolated. The apparent size of the fraction, as determined by gel filtration, was similar to that of dextran blue. Following acid hydrolysis the monomer content of the polysaccharide preparation was studied using high pressure liquid and thin layer chromatography. Glucose, galactose, arabinose, and ribose were the main monosaccharide compounds. The native polysaccharide preparation interacted strongly with the cytosolic isozyme of phosphorylase (EC 2.4.1.1). Interaction with the plastidic phosphorylase isozyme(s) was by far weaker. Interaction with the cytosolic isozyme was demonstrated by affinity electrophoresis, kinetic measurements, and by 14C-labeling experiments in which the glucosyl transfer from [14C]glucose 1-phosphate to the polysaccharide preparation was monitored. 相似文献
172.
Water-storage capacity was measured inThuja occidentalis L.,Tsuga canadensis (L.) Carr., andAcer saccharum Marsh. during the dehydration of stem segments 1.5–2.5 cm in diameter. Stem water potential was measured with a temperature-corrected
stem hygrometer and cavitations were detected acoustically. Water loss was measured by weight change. Dehydration isotherms
consistently displayed three phases. The first phase, from water potential (Ψ) 0 to about −0.2 MPa, had a high capacitance
(C>0.4kg water lost· (1 of tissue)−1· MPa−1) and we have attributed this high C to capillary water as defined by Zimmermann (1983, Xylem structure and the ascent of
sap, Springer-Verlag). The second phase from Ψ=−0.5 to about −2.0 had the lowest C values (<0.02 kg·l−1·MPa−1) and was accompanied by a few cavitation events. This phase may have been a transition zone between capillary storage and
water released by cavitation events as well as water drawn from living cells of the bark. The third phase also had a high
C (about 0.07–0.22kg·l−1·MPa−1) and was associated with many cavitation events while Ψ declined below about −2.5 MPa; we presume the high capacitance was
the consequence of water released by cavitation events. We discuss the ecological adaptive advantage of these three phases
of water-storage in trees. In moist environments, water withdrawn from capillary storage may be an important fraction of transpiration,
but may be of little adaptive advantage. For most of the growth season trees draw mainly on elastic storage, but stem elastic
storage is less than leaf elastic storage and therefore unlikely to be important. In very dry environments, water relased
by cavitation events might be important to the short-term survival of trees. 相似文献
173.
Transgenetic studies implicate interactions between homologous PrP isoforms in scrapie prion replication 总被引:55,自引:0,他引:55
S B Prusiner M Scott D Foster K M Pan D Groth C Mirenda M Torchia S L Yang D Serban G A Carlson 《Cell》1990,63(4):673-686
Transgenic (Tg) mice expressing both Syrian hamster (Ha) and mouse (Mo) prion protein (PrP) genes were used to probe the mechanism of scrapie prion replication. Four Tg lines expressing HaPrP exhibited distinct incubation times ranging from 48 to 277 days, which correlated inversely with HaPrP mRNA and HaPrPC. Bioassays of Tg brain extracts showed that the prion inoculum dictates which prions are synthesized de novo. Tg mice inoculated with Ha prions had approximately 10(9) ID50 units of Ha prions per gram of brain and less than 10 units of Mo prions. Conversely, Tg mice inoculated with Mo prions synthesized Mo prions but not Ha prions. Similarly, Tg mice inoculated with Ha prions exhibited neuropathologic changes characteristic of hamsters with scrapie, while Mo prions produced changes similar to those in non-Tg mice. Our results argue that species specificity of scrapie prions resides in the PrP sequence and prion synthesis is initiated by a species-specific interaction between PrPSc in the inoculum and homologous PrPC. 相似文献
174.
Functional antagonism between oncoprotein c-Jun and the glucocorticoid receptor 总被引:121,自引:0,他引:121
R Schüle P Rangarajan S Kliewer L J Ransone J Bolado N Yang I M Verma R M Evans 《Cell》1990,62(6):1217-1226
175.
The effects of the three dihydropyridine calcium channel agonists (+/-)BAY K 8644, (+)202-791 and (+/-)CGP 28392 on 45Ca++ uptake were studied in cultures of rabbit aortic smooth muscle cells. At 10(-7) M each agonist enhanced 45Ca++ uptake in 15-50 mM K+ but had no effect on the basal 45Ca++ uptake at 5 mM K+. At the uptake threshold of 15 mM K+ each agonist potentiated 45Ca++ uptake in a dose-dependent manner with half maximal effects at 2.4 nM for (+/-)BAY K 8644, 22 nM for (+)202-791 and 18 nM for (+/-)CGP 28392. The agonists showed no significant antagonistic activity. Responses were antagonized competitively by nifedipine and non-competitively by (+/-)D-600. The 45Ca++ uptake dose-response curves and the half maximal effects of the three agonists were over the same range of concentrations as their inhibition of [3H]nitrendipine binding to rat ventricular receptor membrane preparations. The data suggest that these cells mimic the calcium uptake by the intact aorta better than commercial vascular smooth muscle lines or cardiac cells. 相似文献
176.
177.
The CD spectrum of certain all-β globular proteins resembles that of unfolded proteins with a characteristic negative band around 200 nm. The conformation of this class is tentatively termed β-II, which had two features that were absent for unfolded proteins. First, β-II proteins usually had CD bands due to aromatic side groups in the near-ultraviolet region. Second, the CD intensities both in the far- and in the near-uv region of these compact and rigid proteins usually showed a sharp transition upon thermal denaturation, whereas those of an unordered form changed linearly with rising temperature. 相似文献
178.
Novel method to extract large amounts of bacteriocins from lactic acid bacteria. 总被引:18,自引:5,他引:13
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Antimicrobial peptides, bacteriocins, produced by lactic acid bacteria were adsorbed on the cells of producing strains and other gram-positive bacteria. pH was a crucial factor in determining the degree of adsorption of these peptides onto cell surfaces. In general, between 93 and 100% of the bacteriocin molecules were adsorbed at pHs near 6.0, and the lowest (< or = 5%) adsorption took place at pH 1.5 to 2.0. On the basis of this property, a novel isolation method was developed for bacteriocins from four genera of lactic acid bacteria. By using this method we made preparations of pediocin AcH, nisin, sakacin A, and leuconocin Lcm1 that were potent and concentrated. This method produced a higher yield than isolation procedures, which rely on precipitation of the bacteriocins from the cell-free culture liquor. It is simple and can be used to produce large quantities of bacteriocins from lactic acid bacteria to be used as food biopreservatives. 相似文献
179.
M F Canto M M Oliva J J Potter E Mezey V W Yang 《Biochemical and biophysical research communications》1992,188(2):684-689
The activity of the rat class I alcohol dehydrogenase (ADH) is enriched in certain tissues including the liver, intestine and testis. The tissue-specific expression of the gene encoding ADH in the rat was studied and found to closely correlate with tissue isozymic activity. A factor designated enhancer-site downstream binding protein (EDBP) was recently identified in the rat liver and found to interact with the proximal promoter of the class I ADH gene. The distribution of EDBP in nuclear extracts obtained from various tissues was examined based on its sequence-specific DNA binding property and found to correlate with tissue ADH expression. These findings suggest that EDBP is potentially a positive regulatory factor which is involved in controlling the tissue-specific expression of the ADH gene. 相似文献
180.
We have evaluated the relative and quantitative changes in long-chain fatty acids in maternal liver, serum, carcass and conceptus (fetuses plus placentae) during pregnancy in the rat, to ascertain whether previous concern over lower proportions of n - 6 and n - 3 fatty acids in maternal serum could be indicative of suboptimal n - 6 or n - 3 fatty acid status. Gestational hyperlipidemia was characterized by proportional decreases in linoleic, stearic and arachidonic acids but increases in palmitic and docosahexaenoic acids. However, the quantitative amount (microgram/ml) of linoleic, arachidonic and docosahexaenoic acids in serum lipids actually increased 2-5-fold from mid-pregnancy to term. Compared to non-pregnant rats, gestational hyperlipidemia was also associated with a lower proportion but similar quantity of linoleic acid in maternal carcass and adipose stores. We conclude that gestational hyperlipidemia in the rat is characterized by a relative but not quantitative decrease in whole-body stores of n - 6 fatty acids and a marked proportional and quantitative increase in docosahexaenoic acid in maternal organs and in the conceptus. 相似文献