The steady-state internal redox state (NADH/NAD) reflects the external redox state and is correlated with catabolic adaptation in Escherichia coli

Escherichia coli MC4100 was grown in anaerobic glucose-limited chemostat cultures, either in the presence of an electron acceptor (fumarate, nitrate, or oxygen) or fully fermentatively. The steady-state NADH/NAD ratio depended on the nature of the electron acceptor. Anaerobically, the ratio was highest, and it decreased progressively with increasing midpoint potential of the electron acceptor. Similarly, decreasing the dissolved oxygen tension resulted in an increased NADH/NAD ratio. As pyruvate catabolism is a major switch point between fermentative and respiratory behavior, the fluxes through the different pyruvate-consuming enzymes were calculated. Although pyruvate formate lyase (PFL) is inactivated by oxygen, it was inferred that the in vivo activity of the enzyme occurred at low dissolved oxygen tensions (DOT 相似文献   

Freshwater snails and Schistosomiasis mansoni in the state of Rio de Janeiro, Brazil: IV - Sul Fluminense Mesoregion

In this paper, the forth of a series dealing with the survey of freshwater gastropods of the state of Rio de Janeiro, the results of collections carried out in the Sul Fluminense Mesoregion from 2000 to 2002 are presented and revealed the occurrence of 18 species: Antillorbis nordestensis; Biomphalaria glabrata; Biomphalaria peregrina; Biomphalaria straminea; Biomphalaria tenagophila; Drepanotrema anatinum; Drepanotrema cimex; Drepanotrema lucidum; Ferrissia sp.; Gundlachia ticaga; Gundlachia sp.; Heleobia sp.; Lymnaea columella; Melanoides tuberculatus; Physa acuta; Physa marmorata; Pomacea sordida and Pomacea sp. As to the snail hosts of Schistosoma mansoni the most frequent species was B. tenagophila, found in all municipalities surveyed, except Parati. Besides new records the present study extends the distribution of B. peregrina and B. straminea in the state. No specimens were found harbouring larval forms of S. mansoni although different kinds of cercariae had been observed. An account about the current schistosomiasis transmission sites in this Mesoregion is presented as well.     

Concurrence of fragile X and Klinefelter syndromes: report of a new case of paternal nondisjunction

The concurrence of fragile X and Klinefelter syndromes would be expected occasionally. Therefore, the analysis of the literature showed that the concurrence of both conditions was found at least 16 times. Among them, only seven cases were analyzed for the parental origin of the extra chromosome X, suggesting that the maternal nondisjunction was preferentially inherited. We present the third patient with the concurrence of fragile X and Klinefelter syndromes, in which the parental origin of the supernumerary chromosome X was paternal. This finding reinforces that the parent-of-origin predisposition of the concurrence of the fragile X and Klinefelter syndromes is a pure coincidence.     

Organic solvents order the dynamic switch II in Ras crystals

Room temperature crystal structures of crosslinked H-Ras bound to GMPPNP were solved in 50% 2,2,2-trifluoroethanol, 60% 1,6-hexanediol, and 50% isopropanol. The disordered switch II region of Ras is ordered in the presence of 2,2,2-trifluoroethanol or 1,6-hexanediol. The overall backbone conformation of switch II in these organic solvents is the same as in the Ras-GMPPNP complexes with RalGDS, PI(3) kinase, and RasGAP, indicating a biologically relevant form. Key polar interactions that stabilize the ordered switch are enhanced in the presence of hydrophobic cosolvents. These results suggest that hydrophobic solvents can be used in general to order short biologically relevant segments of disordered regions in protein crystals by favoring H-bonding interactions between atoms that are highly solvated and mobile in aqueous solution.     

Effects of a hexokinase II deletion on the dynamics of glycolysis in continuous cultures of Saccharomyces cerevisiae

In glucose-limited aerobic chemostat cultures of a wild-type Saccharomyces cerevisiae and a derived hxk2 null strain, metabolic fluxes were identical. However, the concentrations of intracellular metabolites, especially fructose 1,6-bisphosphate, and hexose-phosphorylating activities differed. Interestingly, the hxk2 null strain showed a higher maximal growth rate and higher Crabtree threshold dilution rate, revealing a higher oxidative capacity for this strain. After a pulse of glucose, aerobic glucose-limited cultures of wild-type S. cerevisiae displayed an overshoot in the intracellular concentrations of glucose 6-phosphate, fructose 6-phosphate, and fructose 1,6-bisphosphate before a new steady state was established, in contrast to the hxk2 null strain which reached a new steady state without overshoot of these metabolites. At low dilution rates the overshoot of intracellular metabolites in the wild-type strain coincided with the immediate production of ethanol after the glucose pulse. In contrast, in the hxk2 null strain the production of ethanol started gradually. However, in spite of the initial differences in ethanol production and dynamic behaviour of the intracellular metabolites, the steady-state fluxes after transition from glucose limitation to glucose excess were not significantly different in the wild-type strain and the hxk2 null strain at any dilution rate.     

Effect of a chayotte (Sechium edule) extract on the labeling of red blood cells and plasma proteins with technetium-99m: in vitro and in vivo studies.

Sechium edule (chayotte) is used as food or as medication in popular medicine. The labeling of blood elements with technetium-99m (99mTc) has been altered by drugs (synthetic and natural). Some authors have reported biological effects concerning the chayotte. We have evaluated the influence of chayotte extracts (macerated and infusion) on the labeling of blood elements with 99mTc. In vitro study, blood was incubated with the extracts, (6.25, 12.5, 25, 50 and 100% v/v). In in vivo study, the animals were treated with the extracts (100% v/v), as drinking water (15 and 60 days) and samples of blood were withdrawn. The blood samples were incubated with stannous chloride and with 99mTc. Plasma (P) and blood cells (BC) were isolated, also precipitated with trichloroacetic acid and soluble (SF) and insoluble fractions (IF) separated. There was a (p < 0.05) decrease in the radioactivity in BC, IF-BC and IF-P with the infusion (100%) and a slight decrease in the uptake of 99mTc by BC and a strong decrease in the fixation in IF-P with the macerated when the extracts were administrated in vivo (15 days). In 60 days, there was a decrease in BC (98.77 to 53.53%), in IF-BC (90.36 to 21.20%) and in IF-P (77.20 to 11.01%). In vitro study no alterations on the labeling of blood elements were found, however, we have found alterations on the fixation of 99mTc in the in vivo study, probably, due to the metabolization of chayotte capable to induce the generation of active metabolites.     

Improved rapid sampling for in vivo kinetics of intracellular metabolites in Saccharomyces cerevisiae.

An integrated approach is used to develop a rapid sampling strategy for the quantitative analysis of in vivo kinetic behavior based on measured concentrations of intracellular metabolites in Saccharomyces cerevisiae. Emphasis is laid on small sample sizes during sampling and analysis. Subsecond residence times are accomplished by minimizing the dead volume of the sterile sampling system and by maximizing flow rates through application of vacuum to the sampling tubes in addition to the overpressure in the fermenter. A specially designed sample tube adapter facilitates sampling intervals of 4 to 5 s for various test tube types. Statistical analysis of the results obtained from enzymatic and liquid chromatography mass spectrometry (LC-MSMS) analysis of the metabolite concentrations was used to optimize the sampling protocol. The most notable improvement is reached through the introduction of vacuum drying of the cell extract. The presented system is capable of reliably dealing with fermenter samples as small as 1-g with a variation of less than 3%, and is thus ideally suited for intracellular measurements on small, lab-scale fermenters.     

Characterization of novel structures of mannosylinositolphosphorylceramides from the yeast forms of Sporothrix schenckii.

Novel structures of glycoinositolphosphorylceramide (GIPC) from the infective yeast form of Sporothrix schenckii were determined by methylation analysis, mass spectrometry and NMR spectroscopy. The lipid portion was characterized as a ceramide composed of C-18 phytosphingosine N-acylated by either 2-hydroxylignoceric acid (80%), lignoceric (15%) or 2,3-dihydroxylignoceric acids (5%). The ceramide was linked through a phosphodiester to myo-inositol (Ins) which is substituted on position O-6 by an oligomannose chain. GIPC-derived Ins oligomannosides were liberated by ammonolysis and characterized as: Manpalpha1-->6Ins; Manpalpha1-->3Manpalpha1-->6Ins; Manpalpha1-->6Manpalpha1-->3Manpalpha1-->3Manpalpha1-->6Ins; Manpalpha1-->2Manpalpha1-->6Manpalpha1-->3Manpalpha1-->3Manpalpha1-->6Ins. These structures comprise a novel family of fungal GIPC, as they contain the Manpalpha1-->6Ins substructure, which has not previously been characterized unambigously, and may be acylated with a 2,3 dihydroxylignoceric fatty acid, a feature hitherto undescribed in fungal lipids.     

Photosynthesis of mistletoes in relation to their hosts at various sites in tropical Brazil

 Chlorophyll a fluorescence parameters showing the instantaneous performance and carbon-isotope ratios reflecting long-term behaviour of leaves were determined for a large number of mistletoe/host-pairs in the cerrado belt of Brazil. Study sites were a very exposed rupestrian field, a semi-exposed savanna and a highly shaded gallery forest. The major question asked was if photosynthetic capacity of mistletoe leaves differed from that of the leaves of their respective hosts. It is shown that except for the very exposed rupestrian field site, photosynthetic capacity appeared to be similar in mistletoes and host leaves. The superior behaviour of host leaves in the rupestrian field was due to particularly expressed sun-plant characteristics of the host. However, mistletoes always had higher average stomatal conductances, lower leaf temperatures at similar or even higher irradiance and higher intercellular CO₂-partial pressures than hosts. Photosynthetic performance of mistletoe leaves was independent of whether a given mistletoe species parasitized aluminium-accumulating or non-accumulating host species in the cerrados with their aluminium-rich soils. Received: 7 April 1997 / Accepted: 20 August 1997