Microenvironmental effects on enzyme catalysis. A kinetic study of hydrophobic derivatives of chymotrypsin

The aim of this work was to study the role of hydrophobic interactions in the enzymic activity of chymotrypsin. The amino groups of chymotrypsin were chemically modified by aliphatic aldehydes of various chain lengths - acetaldehyde, butyraldehyde, hexanal - and with two aldehydes of different steric hindrance - benzaldehyde and trimethyl acetaldehyde. After a rapid study of the derivated enzymes, the hexylchymotrypsin has been chosen for its new catalytic properties: the Michaelis constant is not modified and the maximal velocity with N-glutaryl-L-phenylalanine-4-nitroaniline is increased to 164%. The increase is due to the increase of the acylation constant, k2, by 230%. The value of k3 is not modified or less modified. In the modified enzyme, 85% of free amino acids are still able to react with trinitrobenzenesulphonic acid. The optimum pH is shifted by one pH unit towards the alkaline pH. The thermodynamic study shows that the catalytic process itself is not modified. The increase in Vm could be a simple increase of k2 linked to a modification of the site or of the protein. The phenomenon described is very specific and obtained only with one modification, hexanal, and with one enzyme, alpha-chymotrypsin.     

Contribution of Anionic vs. Neutral Polymers to the Formation of Green Rust 1 from γ-FeOOH Bioreduction

To assess the effect of polymeric substances on the biomineralization and stabilization of green rust (GR), the effect of two organic polymers on the transformation of lepidocrocite (γ-FeOOH) to GR vs. magnetite in presence of Shewanella putrefaciens was investigated. These two polymers, generally used as flocculants, are polyacrylic acid (PAA), which bears negatively charged carboxylic groups at neutral pH and is expected to react with cationic hydrolyzed iron species, and polyacrylamide (PAM), which is a neutral polymer that may develop hydrogen bonds with iron nanocolloids. The bioreduction of lepidocrocite by S. putrefaciens was performed under conditions known to yield either magnetite or GR. Each operational condition of interest was investigated with various polymer concentrations from 0.6 to 60 mg g^?1 Fe (10 to 1000 mg l^?1). The final product was characterized using X-ray diffraction and electronic microscopy. The results showed that the formation of GR is favored, with respect to magnetite, to a lesser extent with PAM than with PAA. These results indicated that polymers influence the chemical stability of GR and/or guide the route of biomineralization. Polymer properties, in addition to silica and phosphate concentrations, are then critical parameters that control the secondary iron mineral biomineralization from iron-reducing bacteria.

Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.     

Influence of Cinnamon and Catnip on the Stereotypical Pacing of Oncilla Cats (Leopardus tigrinus) in Captivity

Nonhuman animals in captivity can experience environmental privation that results in their exhibiting abnormal behaviors. Environmental enrichment techniques can help improve their welfare. This study investigated the behavior of 8 zoo-housed oncilla cats (Leopardus tigrinus) in response to 2 odors (catnip and cinnamon) introduced individually into the animals' enclosures for 3 consecutive days. Proportion of scans spent engaging in stereotypical pacing were compared before, during, and after treatments. The addition of cinnamon reduced the proportion of pacing during and after enrichment (Wilcoxon: Z = 3.16, p < .001; Z = 3.16, p < .001, respectively), indicating a prolonged effect of the enrichment on the animals' behavior. Catnip appears to have elicited no significant difference in the stereotypic pacing before, during, or after the enrichment (Friedman: X² = 2.69; p = .260). The results highlight the potential use of cinnamon as a method of environmental enrichment for small captive-housed cats.     

Living with the enemy: parasites and pathogens of the ladybird <Emphasis Type="Italic">Harmonia axyridis</Emphasis>

Harmonia axyridis is an invasive alien predator in many countries across the world. The rapid establishment and spread of this species is of concern because of the threat it poses to biodiversity as a generalist predator. Understanding the mechanisms that contribute to the success of this species as an invader is not only intriguing but also critical to our understanding of the processes governing such invasions. The enemy release hypothesis (ERH) could explain the rapid population growth of many invasive alien species. However, empirical evidence in support of the ERH is lacking. An alternative hypothesis that could explain rapid population growth is evolution of increased competitive ability (EICA). Here we provide an overview of the parasites and pathogens of coccinellids with a particular focus on H. axyridis as a host. We examine the differential susceptibility of host species and highlight the resilience of H. axyridis in comparison to other coccinellids. We recognise the paucity and limitations of available information and suggest that studies, within a life-table framework, comparing life history traits of H. axyridis in both the native and introduced ranges are necessary. We predict that H. axyridis could benefit from both enemy release and EICA within the introduced range but require further empirical evidence.     

Alien arthropod predators and parasitoids: an ecological approach

Invasive alien species (IAS) coupled with climate change have been referred to as a “deadly duo”. Until recently research on invasion biology has centred mainly on alien plants and vertebrates, despite the numerical dominance of alien arthropods. Arthropods are the largest group of IAS worldwide and many can play a beneficial role, particularly in controlling insect and mite pests. Indeed, 1590 terrestrial arthropod species have been identified as alien to Europe but only a fraction has been shown to cause either an ecological or economical impact, yet knowledge is severely limited by a paucity of data. The IOBC/WPRS Working Group “Benefits and Risks of Exotic Biological Control Agents” developed the theme of this special issue to begin to address the limitations in understanding of this important research area. It represents a timely synthesis of current ecological knowledge and research on alien arthropod predators and parasitoids.     

Increase in prevalence of overweight in Dutch children and adolescents: a comparison of nationwide growth studies in 1980, 1997 and 2009

Objective

To assess the prevalence of overweight and obesity among Dutch children and adolescents, to examine the 30-years trend, and to create new body mass index reference charts.

Design

Nationwide cross-sectional data collection by trained health care professionals.Participants: 10,129 children of Dutch origin aged 0–21 years.

Main Outcome Measures

Overweight (including obesity) and obesity prevalences for Dutch children, defined by the cut-off values on body mass index references according to the International Obesity Task Force.

Results

In 2009, 12.8% of the Dutch boys and 14.8% of the Dutch girls aged 2–21 years were overweight and 1.8% of the boys and 2.2% of the girls were classified as obese. This is a two to three fold higher prevalence in overweight and four to six fold increase in obesity since 1980. Since 1997, a substantial rise took place, especially in obesity, which increased 1.4 times in girls and doubled in boys. There was no increase in mean BMI SDS in the major cities since 1997.

Conclusions

Overweight and obesity prevalences in 2009 were substantially higher than in 1980 and 1997. However, the overweight prevalence stabilized in the major cities. This might be an indication that the rising trend in overweight in the Netherlands is starting to turn.     

Behavioral and neural correlates of communication via pointing

Communicative pointing is a human specific gesture which allows sharing information about a visual item with another person. It sets up a three-way relationship between a subject who points, an addressee and an object. Yet psychophysical and neuroimaging studies have focused on non-communicative pointing, which implies a two-way relationship between a subject and an object without the involvement of an addressee, and makes such gesture comparable to touching or grasping. Thus, experimental data on the communicating function of pointing remain scarce. Here, we examine whether the communicative value of pointing modifies both its behavioral and neural correlates by comparing pointing with or without communication. We found that when healthy participants pointed repeatedly at the same object, the communicative interaction with an addressee induced a spatial reshaping of both the pointing trajectories and the endpoint variability. Our finding supports the hypothesis that a change in reference frame occurs when pointing conveys a communicative intention. In addition, measurement of regional cerebral blood flow using H(2)O(15) PET-scan showed that pointing when communicating with an addressee activated the right posterior superior temporal sulcus and the right medial prefrontal cortex, in contrast to pointing without communication. Such a right hemisphere network suggests that the communicative value of pointing is related to processes involved in taking another person's perspective. This study brings to light the need for future studies on communicative pointing and its neural correlates by unraveling the three-way relationship between subject, object and an addressee.     

Nanoparticle induced cell magneto-rotation: monitoring morphology, stress and drug sensitivity of a suspended single cancer cell

Single cell analysis has allowed critical discoveries in drug testing, immunobiology and stem cell research. In addition, a change from two to three dimensional growth conditions radically affects cell behavior. This already resulted in new observations on gene expression and communication networks and in better predictions of cell responses to their environment. However, it is still difficult to study the size and shape of single cells that are freely suspended, where morphological changes are highly significant. Described here is a new method for quantitative real time monitoring of cell size and morphology, on single live suspended cancer cells, unconfined in three dimensions. The precision is comparable to that of the best optical microscopes, but, in contrast, there is no need for confining the cell to the imaging plane. The here first introduced cell magnetorotation (CM) method is made possible by nanoparticle induced cell magnetization. By using a rotating magnetic field, the magnetically labeled cell is actively rotated, and the rotational period is measured in real-time. A change in morphology induces a change in the rotational period of the suspended cell (e.g. when the cell gets bigger it rotates slower). The ability to monitor, in real time, cell swelling or death, at the single cell level, is demonstrated. This method could thus be used for multiplexed real time single cell morphology analysis, with implications for drug testing, drug discovery, genomics and three-dimensional culturing.