Kinetic properties of the glucose 6-phosphatase of the liver from arthritic rats

According to previous reports, adjuvant-induced arthritic rats present reduced activities of the hepatic glucose 6-phosphatase. A kinetic study was done in order to characterize this phenomenon. Microsomes were isolated from livers of arthritic and control rats (Holtzman strain) and the glucose 6-phosphatase was measured at various temperatures (13-37 degrees C) and glucose 6-phosphate concentrations. Irrespective of the temperature, the enzyme from arthritic rats presented a reduction of both V(max) and K(M). Detergent treatment of liver microsomes from control rats increased the activity, but no increase was found when microsomes from arthritic rats were treated in the same way. The mannose 6-phosphatase activity of detergent-treated microsomes from arthritic rats was only 25% of the activity found with detergent-treated microsomes from control rats. Without detergent treatment, the mannose 6-phosphatase activities of both control and arthritic rats were minimal. The activation energy, derived from V(max), was not changed by arthritis. In vivo arthritic rats presented higher hepatic glucose 6-phosphate concentrations, a phenomenon that is consistent with a reduced activity of glucose 6-phosphatase. It was concluded that in arthritic rats, the hydrolase is probably reduced, without a similar change in the translocase activity.     

Acetate as a carbon source for hydrogen production by photosynthetic bacteria

Hydrogen is a clean energy alternative to fossil fuels. Photosynthetic bacteria produce hydrogen from organic compounds by an anaerobic light-dependent electron transfer process. In the present study hydrogen production by three photosynthetic bacterial strains (Rhodopseudomonas sp., Rhodopseudomonas palustris and a non-identified strain), from four different short-chain organic acids (lactate, malate, acetate and butyrate) was investigated. The effect of light intensity on hydrogen production was also studied by supplying two different light intensities, using acetate as the electron donor. Hydrogen production rates and light efficiencies were compared. Rhodopseudomonas sp. produced the highest volume of H2. This strain reached a maximum H2 production rate of 25 ml H2 l(-1) h(-1), under a light intensity of 680 micromol photons m(-2) s(-1), and a maximum light efficiency of 6.2% under a light intensity of 43 micromol photons m(-2) s(-1). Furthermore, a decrease in acetate concentration from 22 to 11 mM resulted in a decrease in the hydrogen evolved from 214 to 27 ml H2 per vessel.     

CD25+ CD4+ T cells regulate the expansion of peripheral CD4 T cells through the production of IL-10

The mechanisms by which the immune system achieves constant T cell numbers throughout life, thereby controlling autoaggressive cell expansions, are to date not completely understood. Here, we show that the CD25(+) subpopulation of naturally activated (CD45RB(low)) CD4 T cells, but not CD25(-) CD45RB(low) CD4 T cells, inhibits the accumulation of cotransferred CD45RB(high) CD4 T cells in lymphocyte-deficient mice. However, both CD25(+) and CD25(-) CD45RB(low) CD4 T cell subpopulations contain regulatory cells, since they can prevent naive CD4 T cell-induced wasting disease. In the absence of a correlation between disease and the number of recovered CD4(+) cells, we conclude that expansion control and disease prevention are largely independent processes. CD25(+) CD45RB(low) CD4 T cells from IL-10-deficient mice do not protect from disease. They accumulate to a higher cell number and cannot prevent the expansion of CD45RB(high) CD4 T cells upon transfer compared with their wild-type counterparts. Although CD25(+) CD45RB(low) CD4 T cells are capable of expanding when transferred in vivo, they reach a homeostatic equilibrium at lower cell numbers than CD25(-) CD45RB(low) or CD45RB(high) CD4 T cells. We conclude that CD25(+) CD45RB(low) CD4 T cells from nonmanipulated mice control the number of peripheral CD4 T cells through a mechanism involving the production of IL-10 by regulatory T cells.     

Detection of novel sequence heterogeneity and haplotypic diversity of HLA class II genes

Nucleic acid sequences of the second exons of HLA-DRB1, –DRB3/4/5, –DQB1, and –DQA1 genes were determined from 43 homozygous cell lines, representing each of the known class II haplotypes, and from 30 unrelated Caucasian subjects, comprising 60 haplotypes. This systematic sequence analysis was undertaken in order to a) determine the existence of sequence microheterogeneity among cell lines which type as identical by methods other than sequencing; b) determine whether direct sequencing of class II genes will identify the presence of more extensive sequence polymorphism at the population level than that identified with other typing methods; c) accurately determine the molecular composition of the known class II haplotypes; and d) study their evolutionary relatedness by maximum parsimony analysis. The identification of seven previously unidentified haplotypes carrying five new allelic amino acid sequences suggests that sequence microheterogeneity at the population level may be more frequent than previously thought. Maximum parsimony analysis of these haplotypes allowed their evolutionary classification and indicates that the higher mutation rate at DRB1 compared to DQB1 loci in most haplotypic groups is inversed in specific haplotype lineages. Furthermore, the extent and localization of gene conversions and point mutations at class II loci in the evolution of these haplotypes is significantly different at each locus. Identification of additional HLA class II molecular microheterogeneity suggests that direct sequence analysis of class II HLA genes can uncover new allelic sequences in the population and may represent a useful alternative to current typing methodologies to study the effects of sequence allelism in organ transplantation.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession numbers M35890 through M35953.     

Plasma membrane Mg(2+)-ATPase of Pachysolen tannophilus: characterization and role in alcohol tolerance.

Following cell fractionation in sucrose density gradients, plasma membrane Mg(2+)-ATPase from Pachysolen tannophilus was studied. The ATPase displayed an apparent Km for ATP of 1.42 mM and was inhibited by high concentrations of Mg2+. The inhibitory effects of ethanol, 1-propanol, 1-butanol, and benzyl alcohol on Mg(2+)-ATPase were evaluated, and the concentration of each alcohol that inhibited ATPase activity by 50% (IC50) was determined. The IC50 decreased as the chain length of the alcohol increased. Moreover, the IC50 for ATPase activity was similar to the IC50 for growth rate, suggesting an association between impaired growth and ATPase inhibition. Almost complete inhibition of ATPase activity occurred at temperatures approaching 60 degrees C, and the optimal temperature was around 44 degrees C for ATPase from both control and ethanol-treated cells. Inclusion of 50 mM MgCl2 or CaCl2 in the medium did not rescue cells from the deleterious effects of ethanol.     

Swimming training induces liver adaptations to oxidative stress and insulin sensitivity in rats submitted to high-fat diet

Oxidative stress, physical inactivity and high-fat (FAT) diets are associated with hepatic disorders such as metabolic syndrome (MS). The therapeutic effects of physical training (PT) were evaluated in rats with MS induced by FAT diet for 13 weeks, on oxidative stress and insulin signaling in the liver, during the last 6 weeks. FAT-sedentary (SED) rats increased body mass, retroperitoneal fat, mean arterial pressure (MAP) and heart rate (HR), and total cholesterol, serum alanine aminotransferase, glucose and insulin. Livers of FAT-SED rats increased superoxide dismutase activity, thiobarbituric acid-reactive substances, protein carbonyl and oxidized glutathione (GSSG); and decreased catalase activity, reduced glutathione/GSSG ratio, and the mRNA expression of insulin receptor substrate 1 (IRS-1) and serine/threonine kinase 2. FAT-PT rats improved in fitness and reduced their body mass, retroperitoneal fat, and glucose, insulin, total cholesterol, MAP and HR; and their livers increased superoxide dismutase and catalase activities, the reduced glutathione/GSSG ratio and the expression of peroxisome proliferator-activated receptor gamma and insulin receptor compared to FAT-SED rats. These findings indicated adaptive responses to PT by restoring the oxidative balance and insulin signaling in the liver and certain biometric and biochemical parameters as well as MAP in MS rats.     

Bioerosion caused by foraging of the tropical chiton Acanthopleura gemmata at One Tree Reef, southern Great Barrier Reef

The bioerosive potential of the intertidal chiton Acanthopleura gemmata on One Tree Reef was determined by quantification of CaCO₃ in daily faecal pellet production of individuals transplanted into mesocosms after nocturnal-feeding forays. Mean bioerosive potential was estimated at 0.16 kg CaCO₃ chiton⁻¹ yr⁻¹. Bioerosion rates were estimated for populations on two distinct chiton habitats, reef margin (0.013 kg CaCO₃ m⁻² yr⁻¹) and beachrock platform (0.25 kg CaCO₃ m⁻² yr⁻¹). Chiton density on the platform was orders of magnitude greater than on the reef margin. The surface-lowering rate (0.16 mm m⁻² yr) due to bioerosion by the beachrock population is a substantial contribution to the total surface-lowering rate of 2 mm m⁻² yr⁻¹ previously reported for One Tree Reef across all erosive agents. At high densities, the contribution of A. gemmata to coral reef bioerosion budgets may be comparable to other important bioeroders such as echinoids and fish.     

Triple helix conformation of botryosphaeran, a (1→3;1→6)-β-d-glucan produced by Botryosphaeria rhodina MAMB-05

Botryosphaeran, a (1→3;1→6)-β-d-glucan produced by Botryosphaeria rhodina MAMB-05, was found to be present in a triple helix conformation from helix–coil transition studies using Congo Red. The triple helix conformation was disrupted at increasing alkali concentrations. Conformational changes were also observed using phenanthrene as a fluorescent probe, and the fluorescence intensity decreased 80% in the presence of dimethyl sulfoxide. The results confirmed the triple helix conformation of botryosphaeran, an important property manifesting biological response modifying activity.     

Garden bird feeding predicts the structure of urban avian assemblages

Households across the developed world cumulatively spend many millions of dollars annually on feeding garden birds. While beneficial effects on avian assemblages are frequently claimed, the relationships between levels of garden bird feeding and local avian populations are unknown. Using data from a large UK city, we show that both avian species richness and abundance vary across different socioeconomic neighbourhood types. We examined whether patterns in bird feeding could explain this variation. The density of bird feeding stations across the urban environment was strongly positively related to avian abundance, after controlling for differences in habitat availability. This effect was almost exclusively driven by the abundance of those species known to utilize garden feeding stations frequently. In contrast, the density of feeding stations had no effect on avian species richness. We also examined variation in the proportion of households in different communities that provide food for birds, a factor that is not correlated with feeder density. The prevalence of bird feeding across different neighbourhoods declined as socioeconomic deprivation increased, and increased with avian species richness and abundance. Our results suggest that the provision of supplementary food for birds by multiple landowners across a city can impact the status of urban bird populations. The potential for harnessing these actions for conservation needs to be explored.     

Short-term effects of winter warming and acidification on phytoplankton growth and mortality: more losers than winners in a temperate coastal lagoon

Hydrobiologia - Changes in temperature and CO2 are typically associated with climate change, but they also act on shorter time scales, leading to alterations in phytoplankton physiology and...