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81.
Susanne Metzger Andrea Erxleben B. Lippert 《Journal of biological inorganic chemistry》1997,2(2):256-264
The analogy between H-bonded nucleobase pairs and their metalated analogues is extended to the hemiprotonated pair of 7,9-dimethylguanine
(7,9-DimeG) and the Watson-Crick and reversed Watson-Crick pair between 7,9-dimethylguaninium (7,9-DimeGH+) and 1-methylcytosine (1-MeC). The crystal structure analyses of two model compounds, trans–[Pt(CH3NH2)2(7,9-DimeG-N1)2](NO3)2 (1) and trans–[Pt(NH3)2(1-MeC-N3)(7, 9-DimeG-N1)](PF6)2· 2.5 H2O (3a) are reported. Pt binding is through N1 of 7,9-DimeG and N3 of 1-MeC. In solution, 3a exists in a mixture with Watson-Crick and reversed Watson-Crick arrangements of the two bases, depending on solvent, concentration
and anions.
Received: 16 October 1996 / Accepted: 27 January 1997 相似文献
82.
Malin Bäckström Vafa Shahabi Susanne Johansson Susann Teneberg ers Kjellberg Halina Miller-Podraza Jan Holmgren & Michael Lebens 《Molecular microbiology》1997,24(3):489-497
The closely related B-subunits of cholera toxin (CTB) and Escherichia coli heat-labile enterotoxin (LTB) both bind strongly to GM1 ganglioside receptors but LTB can also bind to additional glycolipids and glycoproteins. A number of mutant CT B-subunits were generated by substituting CTB amino acids with those at the corresponding positions in LTB. These were used to investigate the influence of specific residues on receptor-binding specificity. A mutated CTB protein containing the first 25 residues of LTB in combination with LTB residues at positions 94 and 95, bound to the same extent as native LTB to both delipidized rabbit intestinal cell membranes, complex glycosphingolipids (polyglycosylceramides) and neolactotetraosylceramide, but not to non-GM1 intestinal glycosphingolipids. In contrast, when LTB amino acid substitutions in the 1–25 region were combined with those in the 75–83 region, a binding as strong as that of LTB to intestinal glycosphingolipids was observed. In addition, a mutant LTB with a single Gly-33→Asp substitution that completely lacked affinity for both GM1 and non-GM1 glycosphingolipids could still bind to receptors in the intestinal cell membranes and to polyglycosylceramides. We conclude that the extra, non-GM1 receptors for LTB consist of both sialylated and non-sialylated glycoconjugates, and that the binding to either class of receptors is influenced by different amino acid residues within the protein. 相似文献
83.
Susanne J. Andersen 《Antonie van Leeuwenhoek》1995,68(2):165-171
A large number ofPenicillium nalgiovense isolates from mould fermented sausages and the ex type culture were examined for characters of morphology, physiology and production of secondary metabolites. To separate biotypes within theP. nalgiovense species, the data obtained were evaluated using multivariate statistical methods. The macromorphological characters of the ex type culture and isolates from meat products appeared to be distinctive. The ex type culture is characterized by a brown reverse on both Czapek yeast extract and malt extract agar while the isolates from meat products have a yellow to orange reverse. Proteolytic and/or lipolytic activity was demonstrated by 75% of the examined cultures and all of them demonstrated ability to utilize lactate as sole carbon source. Growth on creatine sucrose agar was very inhibited and acid production was absent or very weak. TLC analysis showed production of three unknown secondary metabolites that constituted the characteristic profile. HPLC analysis showed production of only three known secondary metabolites; chrysogine (96%), nalgiolaxin and nalgiovensin (9%). The ex type culture produced nalgiolaxin and nalgiovensin but not chrysogine. The chemometric evaluation showed thatP. nalgiovense isolates from meat products from a homogenous species, which can not be divided into biotypes. The only indication of grouping, beside a separation of the ex type culture, was related to the conidium colour (white, turquoise or grey green). The examinedP. nalgiovense isolates showed some resemblance (morphologically and chemically) toP. chrysogenum. 相似文献
84.
The strictly anaerobic homoacetogenic bacteria Acetobacterium woodii and Sporomusa sphaeroides differ with respect to their energy metabolism. Since growth as well as acetate and ATP formation of A. woodii is strictly dependent on Na+, but that of S. sphaeroides is not, the question arose whether these organisms also use different coupling ions for mechanical work, i.e. flagellar rotation.
During growth on fructose in the presence of Na+ (50 mM), cells of A. woodii were vigorously motile, as judged by light microscopy. At low Na+ concentrations (0.3 mM), the growth rate decreased by only 15%, but the cells were completely non-motile. Addition of Na+ to such cultures restored motility instantaneously. Motility, as determined in swarm agar tubes, was strictly dependent on
Na+; Li+, but not K+ partly substituted for Na+. Of the amilorides tested, phenamil proved to be a specific inhibitor of the flagellar motor of A. woodii. Growth and motility of S. sphaeroides was neither dependent on Na+ nor inhibited by amiloride derivatives. These results indicate that flagellar rotation is driven by ΔμNa
+ in A. woodii, but by ΔμH
+ in S. sphaeroides.
Received: 30 May 1995 / Accepted: 31 August 1995 相似文献
85.
Karl-Josef Dietz Susanne Rudloff Agns Ageorges Christoph Eckerskorn Karsten Fischer Bettina Arbinger 《The Plant journal : for cell and molecular biology》1995,8(4):521-529
A tonoplast protein of 31 kDa apparent molecular mass (TpP 31) was isolated from two-dimensional gels. Amino acid sequences were determined from LysC endoproteinase-peptide fragments. Using degenerate oligonucleotides, a corresponding cDNA clone of 1034 bp was isolated from a barley leaf cDNA library. It encodes for subunit E of the vacuolar H+-ATPase, the first one identified in plants so far. The open reading frame extends over 681 bp, encoding a gene product of 227 amino acids and a calculated molecular weight of 26 228 g mol?1. Northern and Western blot analysis indicates constitutive expression of subunit E in all plant organs with only small effects of salt stress. Localization of TpP 31 at the tonoplast was confirmed in fractions of purified vacuolar membrane obtained by free-flow electrophoresis. Immunoprecipitation of newly synthesized 35S-labelled membrane proteins with anti-TpP 31 gave two additional bands with apparent molecular masses of about 53 and 62 kDa. Gel filtration after mild solubilization showed co-purification of TpP 31 with the 55 kDa subunit of the H+-ATPase. Both results provide evidence beyond the sequence homology that TpP 31 is a structural component of the vacuolar H+-ATPase. 相似文献
86.
Deterministic Three-Half-Order Kinetic Model for Microbial Degradation of Added Carbon Substrates in Soil 总被引:7,自引:6,他引:1
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The kinetics of mineralization of carbonaceous substrates has been explained by a deterministic model which is applicable to either growth or nongrowth conditions in soil. The mixed-order nature of the model does not require a priori decisions about reaction order, discontinuity period of lag or stationary phase, or correction for endogenous mineralization rates. The integrated equation is simpler than the integrated form of the Monod equation because of the following: (i) only two, rather than four, interdependent constants have to be determined by nonlinear regression analysis, (ii) substrate or product formation can be expressed explicitly as a function of time, (iii) biomass concentration does not have to be known, and (iv) the required initial estimate for the nonlinear regression analysis can be easily obtained from a linearized form rather than from an interval estimate of a differential equation. 14CO2 evolution data from soil have been fitted to the model equation. All data except those from irradiated soil gave better fits by residual sum of squares (RSS) by assuming growth in soil was linear (RSS = 0.71) as opposed to exponential (RSS = 2.87). The underlying reasons for growth (exponential versus linear), no growth, and relative degradation rates of substrates are consistent with the basic mechanisms from which the model is derived. 相似文献
87.
The subcellular localization of gamma-glutamyltransferase in calf thymocytes was investigated and compared with that of alkaline phosphodiesterase I, alkaline nitrophenyl phosphatase, succinate-tetrazolium oxidoreductase (succinate-INT reductase) and lactate dehydrogenase after two different methods of cell disruption and differential centrifugation. Most of the activity was recovered in the crude membrane fractions (43.0%), but significant amounts co-pelleted with the large-granule (mitochondria) fractions (31%). The specific activity of the gamma-glutamyltransferase in the purified plasma membrane was 30-50 times that of the enzyme in the cell homogenate and had a similar subcellular distribution to the plasma-membrane markers, alkaline phosphodiesterase I and alkaline nitrophenyl phosphatase. It was concluded that gamma-glutamyltransferase was primary a plasma-membrane-bound enzyme, and that its location in other subcellular fractions was probably due to their contamination with plasma-membrane vesicles. 相似文献
88.
89.
Affinity chromatography, a separation technique which makes use of biospecific properties, is well established for the separation of molecules in solution. We applied this method to the subfractionation of biomembranes. Using a microsomal fraction mainly consisting of plasma membrane from rabbit or calf thymocytes, 20–40% of the protein adhered specifically to concanavalin A-Sepharose, whereas the majority of the membrane vesicles were recovered from the effluent. The adherence involved the binding of Con A to membranes, as addition of the hapten sugar α-methyl-mannoside completely prevented separation. The fractions which bound to Con A-Sepharose could be eluted by combining mechanical forces with the addition of α-methyl-mannoside. All fractions exhibited the same vesicular appearance and were identical with respect to the phospholipid cholesterol ratio. The method proved to be highly reproducible and it offers a possible way for the subfractionation of membranes according to their biospecific structure. 相似文献
90.
The appearance rate of l- and d-phenylalanine in the venous blood of rat jejunal loops in vivo is increased up to 60% if the intraluminal solution is mixed more efficiently by the simultaneous perfusion of air. The effect decreases as the luminal concentration is increased to 100 mmol/1. Thus, the apparent Michaelis constants are by 50% lower in the case of the reduced unstirred layer (26 to 17 for l- and 9 to 6 mmol/1 for d-phenylalanine).The enhancement of the absorption and the reduction of the Michaelis constants can be attributed to the reduction of the effective unstirred layer thickness by about 400–500 μm. 相似文献