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21.
The adsorption of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) as well as of other dipolar molecules to the interface of artificial lipid membranes gives rise to a change of the dipole potential between the membrane interior and water. As a consequence of the adsorption of the neutral species, the conductance of planar membranes, observed in the presence of the macrocyclic ion carriers nonactin or valinomycin, may change by many orders of magnitude. Using this effect in combination with a laser-T-jump technique, the kinetics of the adsorption process were measured and were interpreted on the basis of a Langmuir-isotherm. A partition coefficient (at small concentrations) of
HA
=4.7·10–4 cm, a rate constant of desorption k
HA100 s-1 and a maximum surface density N
D=7.7·1013/cm2 were found. The concentration at half saturation is K
HA=2.7·10-4
M.Using these values the membrane conductance induced by the ion carrier nonactin and the shape of the current-voltage relationship as a function of the ligand concentration in water was analyzed. A maxiumum dipole potential of V
D
max
=-239 m V and a contribution of b=3.1·10-15V cm2 per single adsorbed 2,4-D molecule was found. 74% of the dipole potential acts on the inner membrane barrier separating the two interfacial adsorption planes of nonactin. The remainder (26%) favours interfacial complex formation between nonactin and K+ from the aqueous phase. The data hold for membranes formed from dioleoyllecithin in n-decane. 相似文献
22.
甲基紫精(MV)系统中,在对类囊体膜的光合磷酸化(PSP)活力近于完全抑制的二溴百里香醌(DBMIB)浓度下,由类囊体残缺膜与线粒体嵴膜组成的融合膜PSP活力不仅不被抑制,反而受到不同程度的促进。在铁氰化钾(FeCy)系统中,DBMIB对类囊体膜的PSP活力不能完全抑制,同样浓度的DBMIB对融合膜的PSP活力有抑制效应。检测了不同膜在不同系统中,光下耗氧、放氧、FeCy还原和融合效应的关系等,论证了融合膜中电子传递的途径。 相似文献
23.
We have identified by immunoblotting and ADP-ribosylation by cholera toxin and pertussis toxin the presence of Mr 43 and 46 KDa Gs, and 39 and 41 KDa Gi;.. subunits in rat parotid gland plasma membranes but not in granule membranes. A Mr 28 KDa polypeptide that served as substrate for ADP-ribosylation by both cholera toxin and pertussis toxin was present exclusively in granule membranes. Photoaffinity crosslinking of [-32P]GTP showed the presence of high molecular weight GTP-binding proteins (Mr 160,100 KDa) in granule membranes. Six low molecular weight GTP-binding proteins (Mr 21–28 KDa) were differentially distributed in both plasma membranes and granule membranes. The present study identifies various GTP-binding proteins in rat parotid gland plasma membranes and granule membranes, and demonstrates the presence of distinct molecular weight GTP-binding proteins in granule membranes. These granule-associated GTP-binding proteins may be involved in secretory processes. 相似文献
24.
The distribution of the F420-reactive and F420-nonreactive hydrogenases from the methylotrophic Methanosarcina strain Gö1 indicated a membrane association of the F420-nonreactive enzyme. The membrane-bound F420-nonreactive hydrogenase was purified 42-fold to electrophoretic homogeneity with a yield of 26.7%. The enzyme had a specific activity of 359 mol H2 oxidized · min-1 · mg protein-1. The purification procedure involved dispersion of the membrane fraction with the detergent Chaps followed by anion exchange, hydrophobic and hydroxylapatite chromatography. The aerobically prepared enzyme had to be reactivated anaerobically. Maximal activity was observed at 80°C. The molecular mass as determined by native gel electrophoresis and gel filtration was 77000 and 79000, respectively. SDS gel electrophoresis revealed two polypeptides with molecular masses of 60000 and 40000 indicating a 1:1 stoichiometry. The purified enzyme contained 13.3 mol S2-, 15.1 mol Fe and 0.8 mol Ni/mol enzyme. Flavins were not detected. The amino acid sequence of the N-termini of the subunits showed a higher degree of homology to cubacterial uptake-hydrogenases than to F420-dependent hydrogenases from other methanogenic bacteria. The physiological function of the F420-nonreactive hydrogenase from Methanosarcina strain Gö1 is discussed.Abbreviations
transmembrane electrochemical gradient of H-
- CoM-SH
2-mercaptoethanesulfonate
- F420
(N-l-lactyl--l-glutamyl)-l-glutamic acid phospodiester of 7,8-didemethyl-8-hydroxy-5-deazariboflavin-5-phosphate
- F420H2
reduced F420
- HTP-SH
7-mercaptoheptanoylthreonine phosphate
-
Mb.
Methanobacterium
- PMSF
phenylmethyl-sulfonylfluoride
- Cl3AcOH
trichloroacetic acid 相似文献
25.
Shannon R. Barber John Werdel Millie Symbula John Williams Barbara A. Burkett Peyton T. Taylor James K. Roche Christopher P. Crum 《Cancer immunology, immunotherapy : CII》1992,35(1):33-38
Summary Although serological reactivity to human papillomavirus type 16 (HPV-16) proteins has been demonstrated in patients with invasive cervical carcinoma, the degree of seroreactivity to these proteins in women with preinvasive disease and its relationship to the HPV type associated with the disease are unclear. We obtained sera from 27 women undergoing cone biopsy for cervical precursor lesions and 22 controls and analyzed seroreactivity by Western blot to fusion proteins containing portions of the HPV-16 E4, L1 and L2 open-reading frames (ORFs). Positives were analyzed by scanning densitometry and intensity values for each case plotted relative to controls. Cervical biopsy specimens from patients were analyzed for HPV-16 nucleic acids by DNA · DNA in situ hybridization. Mean intensity values for seroreactivity to the pATH-E4 protein approached significance (P = 0.058) and a significantly higher proportion of cases vs controls registered values over 4.0 for pATH-E4 (26% vs 4.5%;P = 0.04) and pATH-L2 (48% vs 18%;P = 0.03) proteins. A significantly higher mean intensity value for E4 was observed for cases containing HPV-16 DNA vs HPV-16 negative cases or controls. Thus, seroreactivity to HPV-16-derived proteins may be more common in women with preinvasive cervical disease, and for some protein targets (E4) may indicate a relatively type-specific response.Supported in part by grants from the National Cancer Institute [CA 47676 (C.P.C.)], American Cancer Society [MV-395 (C.P.C.)] and an institutional support grant (J.K.R.). Dr. Crum is a recipient of a Physician Scientist Award from the National Institute of Allergy and Infectious Disease (AI00628) 相似文献
26.
27.
Setsuzo Tada Katsuya Gomi Katsuhiko Kitamoto Kojiro Takahashi Gakuzo Tamura Shodo Hara 《Molecular & general genetics : MGG》1991,229(2):301-306
Summary Northern blot analysis of glucose-grown and starch-grown mycelia of Aspergillus oryzae R11340 was conducted using the cloned Taka-amylase A (TAA) gene as a probe. The amount of mRNA homologous to the TAA gene was increased when this fungus was grown with starch as a sole carbon source. In order to analyze the induction mechanism, we inserted the Escherichia coli uidA gene encoding -glucuronidase (GUS) downstream of the TAA promoter and introduced the resultant fusion gene into the A. oryzae genome. Production of a functional GUS protein was induced by starch, but not by glucose. When the effects of various sugars on expression of the fusion gene were examined, the results suggested that the expression of the fusion gene was under control of the TAA gene promoter. 相似文献
28.
Morphogenesis of the foetal membranes and placenta of the root-rat (Tachyoryctes splendens (Rüppel))
The morphogenesis of the foetal membranes and placenta of the root-rat Tachyoryctes splendens was studied by light microscopy. Implantation of the blastocyst is antimesometrial. The mode of implantation is secondary interstitial and the decidual reaction is similar to that in other rodents. Amniogenesis is by cavitation with a temporary open epamniotic cavity. Inversion of the yolk sac is complete but the disappearance of the parietal segment occurs relatively late. With the breakdown of both the decidua capsularis and parietalis, the yolk sac wall near the margins of the placenta becomes bathed in a pool of maternal blood and tissue debris resembling the haemophagous organ. The yolk sac villi are well vascularized. The allantoic cavity is persistent up to the limb bud stage. The definitive placenta is haemochorial and shows conspicuous endodermal sinuses or placental pits. 相似文献
29.
High-affinity binding of3H-folate in Triton X-100 solubilized membranes of human liver displayed characteristics, e.g. apparent positive cooperativity, which are typical of specific folate binding. Ultrogel® AcA 44 chromatography of solubilized membranes saturated with3H-folate revealed a major peak of 100 kDa and a minor peak of 25 kDa. The 100 kDa peak could represent a hydrophobic membrane associated molecular form of the protein. This notion was supported by the fact that the two peaks had identical molecular weights as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis with immunoblotting. 相似文献
30.