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31.
Hortensia Rico Enrique Herrero Fernando Miragall Rafael Sentandreu 《Archives of microbiology》1991,156(2):111-114
Depending upon growth temperature, Candida albicans can exhibit two different morphologies, a budding yeast or a mycelium. By studying the distribution of concanavalin A-ferritin particles on the cell wall surface during bud and germ tube formation, we have elucidated the way cell wall extension occurs. Both processes initially require the localized lysis of the wall in order to allow the incorporation of the newly synthesized material. Later on, the cell wall behaves as an elastic structure, allowing extension by an intosusception process and, as a consequence, cell growth.Abbreviation Con A
concanavalin A 相似文献
32.
Effect of Naturally Occurring nif Reiterations on Symbiotic Effectiveness in Rhizobium phaseoli 总被引:2,自引:0,他引:2 下载免费PDF全文
David Romero Paul W. Singleton Lorenzo Segovia Enrique Morett B. Ben Bohlool Rafael Palacios Guillermo Dvila 《Applied microbiology》1988,54(3):848-850
Most naturally occurring strains of Rhizobium phaseoli possess reiteration of the nif genes. Three regions contain nitrogenase structural genes in strain CFN42. Two of these regions (a and b) have copies of nifH, nifD, and nifK, whereas the third region (c) contains only nifH. Strains containing mutations in either nif region a or nif region b had significantly diminished symbiotic effectiveness compared with the wild-type strain on the basis of nodule mass, total nitrogenase activity per plant, nitrogenase specific activity, total nitrogen in the shoot, and percentage of nitrogen. A strain containing mutations in both nif region a and nif region b was totally ineffective. These data indicate that both nif region a and nif region b are needed for full symbiotic effectiveness in R. phaseoli. 相似文献
33.
Ras oncogene mediated induction of a 92 kDa metalloproteinase; strong correlation with the malignant phenotype 总被引:11,自引:0,他引:11
M Ballin D E Gomez C C Sinha U P Thorgeirsson 《Biochemical and biophysical research communications》1988,154(3):832-838
We have previously demonstrated that activated ras oncogenes can induce the metastatic phenotype and type IV collagenolytic activity in NIH/3T3 cells (Thorgeirsson et al. Mol. Cell. Biol. 5:259-262, 1985). The present study demonstrates ras-mediated induction of a 92 kDa metalloproteinase, which degrades gelatin and type IV collagen. Association of the 92 kDa proteinase expression with the malignant phenotype was also observed in human tumor cell lines. Our data indicate that the 92 kDa gelatin-collagen IV degrading metalloproteinase is an important participant in the proteolytic process involving tumor cell invasion and metastasis. 相似文献
34.
Stanley A. Mendoza Abelardo Lopez-Rivas James W. Sinnett-Smith Enrique Rozengurt 《Experimental cell research》1986,164(2)
Vasopressin increased intracellular free calcium concentration [Ca2+]i in quin-2-loaded quiescent Swiss 3T3 cells. This effect of vasopressin was rapidly inhibited by biologically active tumour promoters including phorbol dibutyrate (PBt2) and by the synthetic diacylglycerol 1-oleoyl-2-acetyl-glycerol (OAG). Prolonged pretreatment of Swiss 3T3 cells with PBt2 causes a loss of protein kinase C activity (Rodriguez-Pena & Rozengurt, Biochem biophys res commun 120 (1984) 1053) [28]. This pretreatment abolished the inhibition by PBt2 or OAG of vasopressin-mediated increases in Ca2+]i. Vasopressin also stimulated 45Ca2+ efflux from cells pre-loaded with the isotope. This effect of the hormone was also inhibited by PBt2. Prolonged pretreatment with PBt2 prevented the inhibition of vasopressin-stimulated 45Ca2+ release by PBt2. Thus, protein kinase C stimulation inhibits vasopressin-mediated increases in [Ca2+]i and 45Ca2+ efflux apparently by blocking the increased release of Ca2+ from an intracellular store caused by the hormone. These findings suggest that activation of protein kinase C may act as a feedback inhibitor to modulate ligand-mediated increases in [Ca2+]i. 相似文献
35.
Mortimer M. Civan Stephen R. Williams David G. Gadian Enrique Rozengurt 《The Journal of membrane biology》1986,94(1):55-64
Summary Swiss mouse 3T3 cells grown on microcarrier beads were superfused with electrolyte solution during continuous NMR analysis. Conventional31P and19F probes of intracellular pH (pH
c
) were found to be impracticable. Cells were therefore superfused with 1 to 4mm 2-deoxyglucose, producing a large intracellular, pH-sensitive signal of 2-deoxyglucose phosphate (2DGP). The intracellular incorporation of 2DGP inhibited the Embden-Meyerhof pathway. However, intracellular ATP was at least in part retained and the cellular responsivity to changes in extracellular ionic composition and to the application of growth factors proved intact. Transient replacement of external Na+ with choline or K+ reversibly acidified the intracellular fluids. Quiescent cells and mitogenically stimulated cells displayed the same dependence of shifts in pH
c
on external Na+ concentration (c
Na
o
). pH
c
also depended on intracellular Na+ concentration (c
Na
o
). Increasingc
Na
c
by withdrawing external K+ (thereby inhibiting the Na,K-pump) caused reversible intracellular acidification; subsequently reducingc
Na
o
produced a larger acid shift in pH
c
than with external K+ present. Comparison of separate preparations indicated that pH
c
was higher in stimulated than in quiescent cells. Transient administration of mitogens also reversibly alkalinized quiescent cells studied continuously. This study documents the feasibility of monitoring pH
c
of Swiss mouse 3T3 cells using31P NMR analysis of 2DGP. The results support the concept of a Na/H antiport operative in these cells, both in quiescence and after mitogenic stimulation. The data document by an independent technique that cytoplasmic alkalinization is an early event in mitogenesis, and that full activity of the Embden-Meyerhof pathway is not required for the expression of this event. 相似文献
36.
The relative proportions of both somatostatin-14 and its precursors somatostatin-28 and the 15 Kdalton prosomatostatin were evaluated by radioimmunoassay in the cerebrospinal fluid of patients with Alzheimer's disease. It was observed that the patients have a lowered content in the tetradecapeptide somatostatin while they exhibit a significant increase in unprocessed 15 Kda precursor. These results indicate that these patients possess impaired processing mechanisms which may be responsible for the lowered content in mature somatostatin-14. These observations may provide a valuable test for the ante-mortem diagnosis of the disease. They are discussed in connection with others suggesting that Alzheimer's patients may be selectively altered in their somatostatinergic neurones of their cerebral cortex (Morrison et al. (1985) Nature 314, 90-92. Roberts et al. (1985) Nature 314, 92-94). 相似文献
37.
Amygdala kindled seizure stage is related to altered benzodiazepine binding site density 总被引:1,自引:0,他引:1
Benzodiazepine receptor binding was examined in rats at 3 stages of amygdaloid kindling (i.e., initial afterdischarge, Stage 3 and Stage 5) immediately or 24 hr after seizure. 3H-diazepam binding site density (Bmax) was significantly increased 24 hr after Stage 3 and Stage 5 kindled seizures in the hippocampus but not in the amygdala. There were no significant differences in the dissociation constants (KD) between kindled and control rats at any time point examined for either brain region. These results demonstrate that changes in benzodiazepine binding are observed with partial kindled seizures (i.e., Stage 3), indicating that generalized seizures are not prerequisite to increased benzodiazepine receptor site density. 相似文献
38.
Xanthine dehydrogenase from chicken liver is a dimeric enzyme, each hemimolecule containing one FAD and two Fe/S groups. Determination of sulfhydryl groups with 5,5-dithiobis(2-nitrobenzoic acid) (DTNB) andp-hydroxymercuribenzoic acid (PMB) showed a variable number of sulfhydryl groups depending onpH, ionic strength, and nature of the reaction medium and buffer. The number of disulfide bonds was determined with DTNB and reducing conditions. Amino groups were determined with 2,4,6,-trinitrobencensulfonic acid (TNBS). At constant temperature andpH the reaction of DTNB and TNBS with native xanthine dehydrogenase showed an exponential dependence on time. From the obtained parameters the number of available sulfhydryl and amino groups at infinite concentration of enzyme and the rate constant of the equation were determined. The absorption spectrum of the enzyme changed with time when a chaotropic agent (1 M sodium nitrate) was added to the medium. This difference was detected by measuring the absorbance in the range 450–550 nm. The absorption spectrum (between 350 and 600 nm) also changed when a denaturating agent (sodium dodecyl sulfate) was added. This modification increased with time and depended on the medium. 相似文献
39.
Antonio Gomez Sanchez Manuel Mancera Francisco Rosado Manuel Rico 《Carbohydrate research》1984,134(1):75-82
3,4,5,6,7-Penta-O-acetyl-1,2-dideoxy-1-nitro-d-gluco-hept-1-enitol reacts with methyl acetoacetate in an unusual Michael reaction, giving the normal adduct (6), and a bicyclic derivative (9) that arises from quasi-dimerization of the former when a high concentration of the base is used. Acetylation of compound 9 gives the hydroxylamine O-acetate (10).From the reactions of 3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-nitro-d-galacto-hept-1-enitol with ethyl and tert-butyl acetoacetate, the normal adducts (7 and 8) were isolated. The structures of compounds 6 to 10 were established on the basis of their spectral properties (u.v., i.r., mass, and 1H- and 13C-n.m.r.) 相似文献
40.
Incubation of dejellied spawned oocytes from Bufo arenarum with different lectins results in a decrease of oocyte fertility. Concanavalin A was the most effective lectin; phytohem-agglutinin P and wheat germ lectin were less effective. Agglutinin from soybean was scarcely active. These lectin effects could be ascribed to a hindering of specific sites for some proteases, since the same treatment renders the oocyte vitelline envelope insensitive to spermatolysin (an essential requisite for fertilization) and to trypsin. Also in this case concanavalin A was the most effective lectin. Univalent concanavalin A was also effective in blocking the fertility of dejellied oocytes. These results indicate that the residues of α-D-glucose and α-D-mannose present in the vitelline envelope are involved in gamete interactions in Bufo arenarum. This idea is also supported by the finding that dejellied oocytes (fertilizables) have a number of binding sites for concanavalin A that is three or four orders of magnitude higher than coelomic or fertilized oocytes (both not penetrable by spermatozoa). 相似文献