Carnivory and active hunting by the planktonic testate amoeba <Emphasis Type="Italic">Difflugia tuberspinifera</Emphasis>

Difflugia tuberspinifera, a testate amoeba found in the open water plankton of Liuxi He and other south Chinese reservoirs during summer, is one of six or more species that occasionally live a pelagic life. Here, we suggest that its incentive to leave the bottom might be the abundance of food in the water column rather than temperature. This Difflugia (and perhaps the other pelagic species as well) is indeed an actively hunting carnivore that catches small rotifers and other prey in the same size range. In Liuxi He, it readily feeds on Collotheca cf. mutabilis, which it catches and consumes with remarkable agility: it first inspects the jelly tube that protects the prey, then moves to the bottom of it, perforates the jelly near the prey’s foot, and finally ingests the rotifer foot-first.     

Incorporating dipolar solvents with variable density in Poisson-Boltzmann electrostatics

We describe a new way to calculate the electrostatic properties of macromolecules that goes beyond the classical Poisson-Boltzmann treatment with only a small extra CPU cost. The solvent region is no longer modeled as a homogeneous dielectric media but rather as an assembly of self-orienting interacting dipoles of variable density. The method effectively unifies both the Poisson-centric view and the Langevin Dipole model. The model results in a variable dielectric constant in the solvent region and also in a variable solvent density that depends on the nature of the closest exposed solute atoms. The model was calibrated using small molecules and ions solvation data with only two adjustable parameters, namely the size and dipolar moment of the solvent. Hydrophobicity scales derived from the solvent density profiles agree very well with independently derived hydrophobicity scales, both at the atomic or residue level. Dimerization interfaces in homodimeric proteins or lipid-binding regions in membrane proteins clearly appear as poorly solvated patches on the solute accessible surface. Comparison of the thermally averaged solvent density of this model with the one derived from molecular dynamics simulations shows qualitative agreement on a coarse-grained level. Because this calculation is much more rapid than that from molecular dynamics, applications of a density-profile-based solvation energy to the identification of the true structure among a set of decoys become computationally feasible. Various possible improvements of the model are discussed, as well as extensions of the formalism to treat mixtures of dipolar solvents of different sizes.     

Yeast, a model organism for iron and copper metabolism studies

Virtually all organisms on earth depend on transition metals for survival. Iron and copper are particularly important because they participate in vital electron transfer reactions, and are thus cofactors of many metabolic enzymes. Their ability to transfer electrons also render them toxic when present in excess. Disturbances of iron and copper steady-state levels can have profound effects on cellular metabolism, growth and development. It is critical to maintain these metals in a narrow range between utility and toxicity. Organisms ranging from bacteria and plants to mammals have developed sophisticated mechanisms to control metal homeostasis. In this review, we will present an overview of the current understanding of iron and copper metabolism in yeast, and the utility of yeast as a model organism to investigate iron and copper metabolism in mammals and plants.     

Influence of Nutritional Factors on the Nature, Yield, and Composition of Exopolysaccharides Produced by Gluconacetobacter xylinus I-2281

The influence of substrate composition on the yield, nature, and composition of exopolysaccharides (EPS) produced by the food-grade strain Gluconacetobacter xylinus I-2281 was investigated during controlled cultivations on mixed substrates containing acetate and either glucose, sucrose, or fructose. Enzymatic activity analysis and acid hydrolysis revealed that two EPS, gluconacetan and levan, were produced by G. xylinus. In contrast to other acetic acid strains, no exocellulose formation has been measured. Considerable differences in metabolite yields have been observed with regard to the carbohydrate source. It was shown that glucose was inadequate for EPS production since most of this substrate (0.84 C-mol/C-mol) was oxidized into gluconic acid, 2-ketogluconic acid, and 5-ketogluconic acid. In contrast, sucrose and fructose supported a 0.35 C-mol/C-mol gluconacetan yield. In addition, growing G. xylinus on sucrose produced a 0.07 C-mol/C-mol levan yield. The composition of EPS remained unchanged during the course of the fermentations. Levan sucrase activity was found to be mainly membrane associated. In addition to levan production, an analysis of levan sucrase's activity also explained the formation of glucose oxides during fermentation on sucrose through the release of glucose. The biosynthetic pathway of gluconacetan synthesis has also been explored. Although the activity of key enzymes showed large differences to be a function of the carbon source, the ratio of their activities remained similar from one carbon source to another and corresponded to the ratio of precursor needs as deduced from the gluconacetan composition.     

Emotional Eating,Alexithymia, and Binge‐Eating Disorder in Obese Women

Objective: To investigate the relationships between alexithymia and emotional eating in obese women with or without Binge Eating Disorder (BED). Research Methods and Procedures: One hundred sixty‐nine obese women completed self‐report questionnaires, including the Beck Depression Inventory, the State Trait Anxiety Inventory, the Stress Perceived Scale, the Dutch Eating Behaviour Questionnaire, and the Toronto Alexithymia Scale. The presence of BED, screened using the Questionnaire of Eating and Weight Patterns, was confirmed by interview. Results: Forty obese women were identified as having BED. BED subjects and non‐BED subjects were comparable in age, body mass index, educational level, and socioeconomic class. According to the Dutch Eating Behaviour Questionnaire, BED subjects exhibited higher depression, anxiety, perceived stress, alexithymia scores, and emotional and external eating scores than non‐BED subjects. Emotional eating and perceived stress emerged as significant predictors of BED. The relationships between alexithymia and emotional eating in obese subjects differed between the two groups according to the presence of BED. Alexithymia was the predictor of emotional eating in BED subjects, whereas perceived stress and depression were the predictors in non‐BED subjects. Discussion: This study pointed out different relationships among mood, alexithymia, and emotional eating in obese subjects with or without BED. Alexithymia was linked to emotional eating in BED. These data suggest the involvement of alexithymia in eating disorders among obese women.     

Expression and characterization of active site mutants of hevamine, a chitinase from the rubber tree Hevea brasiliensis.

Hevamine is a chitinase from the rubber tree Hevea brasiliensis. Its active site contains Asp125, Glu127, and Tyr183, which interact with the -1 sugar residue of the substrate. To investigate their role in catalysis, we have successfully expressed wild-type enzyme and mutants of these residues as inclusion bodies in Escherichia coli. After refolding and purification they were characterized by both structural and enzyme kinetic studies. Mutation of Tyr183 to phenylalanine produced an enzyme with a lower k(cat) and a slightly higher K(m) than the wild-type enzyme. Mutating Asp125 and Glu127 to alanine gave mutants with approximately 2% residual activity. In contrast, the Asp125Asn mutant retained substantial activity, with an approximately twofold lower k(cat) and an approximately twofold higher K(m) than the wild-type enzyme. More interestingly, it showed activity to higher pH values than the other variants. The X-ray structure of the Asp125Ala/Glu127Ala double mutant soaked with chitotetraose shows that, compared with wild-type hevamine, the carbonyl oxygen atom of the N-acetyl group of the -1 sugar residue has rotated away from the C1 atom of that residue. The combined structural and kinetic data show that Asp125 and Tyr183 contribute to catalysis by positioning the carbonyl oxygen of the N-acetyl group near to the C1 atom. This allows the stabilization of a positively charged transient intermediate, in agreement with a previous proposal that the enzyme makes use of substrate-assisted catalysis.     

Branchinecta oterosanvicentei n. sp. (Branchiopoda: Anostraca), a new fairy shrimp from the Chihuahuan desert, with a proposal for the conservation of the Branchinectidae of Mexico

Branchinecta oterosanvicentei, new species, a fairy shrimp endemic to the south of Coahuila, Mexico is described and figured. Differential features between the new species and the related B. lindahli are discussed on the basis of a SEM micrographs. The main diagnostic characters of Branchinecta oterosanvicentei are: (1) a pulvinus covered by scales localized on the middle of the median side of the proximal article of antenna, and (2) a network of prominent cortical crests on the cyst surface. Of seven Branchinecta species occurring in Mexico, four (B. belki, B. mexicana, B. oterosanvicentei, and B. sandiegonensis) have a restricted geographic range. Because, in addition, extreme fluctuations in the number of mature individuals per population occur, the survival of all of these species is threatened, and measures should be taken to protect them. Branchinecta mackini has a wide distribution in North America, but even this form is rare in Mexico.     

Analysis of the C-Terminal Membrane Anchor Domains of Hepatitis C Virus Glycoproteins E1 and E2: toward a Topological Model

The hepatitis C virus (HCV) glycoproteins E1 and E2 should be anchored in the viral membrane by their C-terminal domains. During synthesis, they are translocated to the endoplasmic reticulum (ER) lumen where they remain. The 31 C-terminal residues of the E1 protein and the 29 C-terminal residues of the E2 protein are implicated in the ER retention. Moreover, the E1 and E2 C termini are implicated in E1-E2 heterodimerization. We studied the E1 and E2 C-terminal sequences of 25 HCV strains in silico using molecular modeling techniques. We conclude that both C-terminal domains should adopt a similar and peculiar configuration: one amphipathic alpha-helix followed by a pair of transmembrane beta-strands. Several three-dimensional (3-D) models were generated. After energy minimization, their ability to interact with membranes was studied using the molecular hydrophobicity potentials calculation and the IMPALA procedure. The latter simulates interactions with a membrane by a Monte Carlo minimization of energy. These methods suggest that the beta-hairpins could anchor the glycoproteins in the ER membrane at least transiently. Anchoring could be stabilized by the adsorption of the nearby amphipathic alpha-helices at the membrane surface. The 3-D models correlate with experimental results which indicate that the E1-E2 transmembrane domains are involved in the heterodimerization and have ER retention properties.     

Determination of the biological diatom index (IBD NF T 90–354): results of an intercomparison exercise

A diatom intercomparison exercise on sampling, slide preparation, countsand identification has been carried out in September 1999 with 24French-speaking diatomists on the River Loup (Alpes Maritimes, France). Fewoperators strictly respected the standard, especially for the number ofindividuals to be counted. It has however been demonstrated this had a very lowimpact on the index value and that old counts can be used for indexcalculation,if there are at least 300 frustules or valves. Counts higher than 400 did notlead to a better precision. The total variability largely depended on theoperator and was distributed unevenly between sampling, which appears to be acritical stage, slide preparation and counting. For those who strictlyrespectedthe standard procedure, the natural variability can be estimated to about oneunit value of the Biological Diatom Index. This intra-operator variability canbe considered as very low, as the IBD scale is from 0 to 20, and notsignificantin assessing water quality. Despite this, the inter-operator variability isgreater. When comparing operators' results, after excluding those who did notrespect the standard requirements, the main source of variability is due tomisidentifications, especially for small Achnanthes(A. minutissima and A. biasolettiana)and Cocconeis (C. placentula var.placentula, var. euglypta and var.lineata). Intercomparison exercises, internet exchangesforchecking and reference material collections should be encouraged both tosatisfythe internal and external quality controls and to acquaint biologists with theimportance of field and laboratory protocols, as well as to allow progress indiatom identification.