Structural analogies between different redox enzymes inserted into biological membranes

• 1.1. We have compared the primary structure and the predicted secondary structure of subunit I (COI) of cytochrome oxidase with those of other integral redox enzymes which contain membrane-buried iron centres.
• 2.2. Some striking analogies have been found between the deduced transmembrane folding for COI and the known three-dimensional structure of the photosynthetic reaction centre of Rhodobacter sphaeroides.
• 3.3. These structural analogies are paralleled by a fundamental functional analogy between these two redox systems, since they both oxidize reduced cytochrome c at the positive side of the membrane, transferring electrons to membrane-buried metal centres.
• 4.4. A statistical evaluation has been performed on the amino acid composition of the peptides containing known histidine ligands of the membrane-buried iron in cytochrome b of the bc 1 complex and in the bacterial reaction centre.
• 5.5. This evaluation was then applied to the peptides which contain conserved histidines in subunit I of cytochrome oxidase, subunit that is known to bind both haem a and a3, indicating which of these histidines are the most likely ligands of the membrane-buried iron of the a-haems.
• 6.6. A sequence homology has been found between the known oxygen binding site and the haem binding peptide in cyt P450 and two peptides which are conserved in all the sequences of COI, thus indicatingt the possible oxygen catalytic site of cytochrome oxidase.

     

Legume inoculant application methods: effects on nodulation patterns,nitrogen fixation,crop growth and yield in narrow-leaf lupin and faba bean

Aims

Plant growth forms can influence carbon cycling, particularly in carbon-rich ecosystems like northern peatlands; however, mechanistic evidence of this relationship is limited. Our aim was to determine if northern peatland plant growth forms alter belowground dissolved carbon chemistry and enhance carbon release through stimulated microbial metabolism.

Methods

We used replicated, peat monoliths populated exclusively by Sphagnum mosses, graminoids, or bare peat and quantified changes in belowground dissolved organic carbon chemistry, microbial metabolism, as well as respired CO₂.

Results

The graminoid growth form was significantly distinct in belowground dissolved organic carbon chemistry with carbon compound lability 20 % and 11 % greater than bare peat and Sphagnum moss respectively. The labile dissolved organic carbon stimulated the microbial community, as indicated by greater microbial metabolic activity and richness values in conjunction with 50 % higher respired CO₂ fluxes under the graminoid treatment.

Conclusions

Our results provide mechanistic evidence that peatland plant growth forms can drive carbon cycling processes by altering dissolved organic carbon chemistry to prompt cascading effects on the microbial community and carbon release — trends suggestive of microbial priming effects. Should climate change increase graminoid prevalence at the expense of Sphagnum moss northern peatland carbon store stability may be threatened by this mechanism.

     

Anatomy,photochemical activity,and DNA polymorphism in leaves of dwarf tomato irradiated with X-rays

The response of higher plants to ionising radiation depends on factors related to both radiation properties and plant features including species, cultivar, age, and structural complexity of the target organ. Adult plants of dwarf tomato were irradiated with different doses of X-rays to investigate possible variations in leaf morpho-anatomical traits, photosynthetic efficiency, and genomic DNA. In order to assess if and how responses depend on leaf developmental stage, we analysed two types of leaves; nearly mature leaves (L1) and actively developing leaves (L2), whose lamina size corresponded to 70 and 25 %, respectively, of the lamina size of the fully expanded leaves. The results show that the X-rays prevented full lamina expansion of the L2 leaves at all doses and induced early death of tissue of plants irradiated with doses higher than 20 Gy. Most anatomical modifications were not clearly dose-dependent and the radiation-induced increase in phenolic compounds was irrespective of dose. At high doses of X-rays (50 and 100 Gy), photochemical efficiency decreased significantly in both leaf types, whereas total chlorophyll content significantly decreased only in the L2 leaves. The random amplification of polymorphic DNA data show that the X-rays induced mutagenic effects in the L2 leaves even at low doses despite the absence of severe phenotypic alterations. Genetic structure found in the population of samples corroborates the results of anatomical and eco-physiological analyses: the 20 Gy dose seems to mark the threshold dose above which genetic alterations, structural anomalies, and perturbations in the photosynthetic apparatus become significant, especially in the actively expanding leaves.     

In vitro increase of the fluid-phase endocytosis induced by pulsed radiofrequency electromagnetic fields: importance of the electric field component

Nowadays, due to the wide use of mobile phones, the possible biological effects of electromagnetic fields (EMF) become a public health general concern. Despite intensive research, there are no widely accepted theories about the interactions between EMFs and living cells, and the experimental data are often controversial. We examined the effects of mobile phones EMF (envelope frequency of 217 Hz, carrier frequency of 900 MHz and pulse duration of 580 μs) or its pure, low-frequency pulsed electric field component on fluid-phase endocytosis. In both cases, with exposures exceeding 10 min, an increase of the fluid-phase endocytosis rate was observed (≈1.5-fold), on three different cell types. This increase is an all-or-nothing type of response that is occurring for threshold values comprised between 1.3 and 2.6 W/kg for the delivered EMF powers and between 1.1 and 1.5 V/cm for the electric fields intensities depending upon the cell type. The electric component of these EMFs is shown to be responsible for the observed increase. Variations of frequency or pulse duration of the electric pulses are shown to be without effect. Thus, EMF, via their electrical component, can perturb one of the most fundamental physiological functions of the cells—endocytosis.     

Light-emitting diodes and cool white fluorescent light similarly suppress pineal gland melatonin and maintain retinal function and morphology in the rat.

BACKGROUND AND PURPOSE: A novel light-emitting diode (LED) light source for use in animal-habitat lighting was evaluated. METHODS: The LED was evaluated by comparing its effectiveness with that of cool white fluorescent light (CWF) in suppressing pineal gland melatonin content and maintaining normal retinal physiology, as evaluated by use of electroretinography (ERG), and morphology. RESULTS: Pineal melatonin concentration was equally suppressed by LED and CWF light at five light illuminances (100, 40, 10, 1, and 0.1 lux). There were no significant differences in melatonin suppression between LED and CWF light, compared with values for unexposed controls. There were no differences in ERG a-wave implicit times and amplitudes or b-wave implicit times and amplitudes between 100-lux LED-exposed rats and 100-lux CWF-exposed rats. Results of retinal histologic examination indicated no differences in retinal thickness, rod outer segment length, and number of rod nuclei between rats exposed to 100-lux LED and 100-lux CWF for 14 days. Furthermore, in all eyes, the retinal pigmented epithelium was intact and not vacuolated, whereas rod outer segments were of normal thickness. CONCLUSION: LED light does not cause retinal damage and can suppress pineal melatonin content at intensities similar to CWF light intensities.     

Pituitary responsiveness to gonadotrophin-releasing and thyrotrophin-releasing hormones in children receiving phenobarbitone.

The effect of long-term treatment with phenobarbitone on pituitary responsiveness to gonadotrophin-releasing hormone and thyrotrophin-releasing hormone was studied in 20 boys being treated with the drug to prevent febrile convulsions. Baseline concentrations of luteinising and follicle-stimulating hormones were reduced as well as the responses of these hormones to stimulation with gonadotrophin-releasing hormone. Baseline prolactin concentrations were raised in comparison with those in normal children. The response of prolactin to thyrotrophin-releasing hormone, however, was impaired only in the children who had been receiving the drug for a long time. Phenobarbitone had no effect on the secretion of growth hormone. Further studies should be carried out to ascertain how long these effects on pituitary function last after phenobarbitone is withdrawn and whether this interference with pituitary function modifies the child''s subsequent development.     

Believing Is Seeing: Fixation Duration Predicts Implicit Negative Attitudes

A prototypical finding of social cognition is that social experiences influence later performance even though those experiences are not introspectively available. Building on social cognition research on implicit attitudes, we evaluate whether ethnic category/attribute pairs influence eye movements during the Implicit Association Test (IAT, Greenwald, McGhee, & Schwartz 1998). Results show that fixation duration predicted implicit attitudes such that when the category/attribute pairs disconfirmed one''s implicit negative attitude fixation duration toward that pair increased. The present research provides evidence that eye movements and implicit processes inherent in the IAT are more broadly connected than previously thought.     

Negative regulation by Ser/Thr phosphorylation of HadAB and HadBC dehydratases from Mycobacterium tuberculosis type II fatty acid synthase system

The type II fatty acid synthase system of mycobacteria is involved in the biosynthesis of major and essential lipids, mycolic acids, key-factors of Mycobacterium tuberculosis pathogenicity. One reason of the remarkable survival ability of M. tuberculosis in infected hosts is partly related to the presence of cell wall-associated mycolic acids. Despite their importance, the mechanisms that modulate synthesis of these lipids in response to environmental changes are unknown. We demonstrate here that HadAB and HadBC dehydratases of this system are phosphorylated by Ser/Thr protein kinases, which negatively affects their enzymatic activity. The phosphorylation of HadAB/BC is growth phase-dependent, suggesting that it represents a mechanism by which mycobacteria might tightly control mycolic acid biosynthesis under non-replicating condition.     

Effects of Pleiotrophin Overexpression on Mouse Skeletal Muscles in Normal Loading and in Actual and Simulated Microgravity

Pleiotrophin (PTN) is a widespread cytokine involved in bone formation, neurite outgrowth, and angiogenesis. In skeletal muscle, PTN is upregulated during myogenesis, post-synaptic induction, and regeneration after crushing, but little is known regarding its effects on muscle function. Here, we describe the effects of PTN on the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles in mice over-expressing PTN under the control of a bone promoter. The mice were maintained in normal loading or disuse condition, induced by hindlimb unloading (HU) for 14 days. Effects of exposition to near-zero gravity during a 3-months spaceflight (SF) into the Mice Drawer System are also reported. In normal loading, PTN overexpression had no effect on muscle fiber cross-sectional area, but shifted soleus muscle toward a slower phenotype, as shown by an increased number of oxidative type 1 fibers, and increased gene expression of cytochrome c oxidase subunit IV and citrate synthase. The cytokine increased soleus and EDL capillary-to-fiber ratio. PTN overexpression did not prevent soleus muscle atrophy, slow-to-fast transition, and capillary regression induced by SF and HU. Nevertheless, PTN exerted various effects on sarcolemma ion channel expression/function and resting cytosolic Ca²⁺ concentration in soleus and EDL muscles, in normal loading and after HU. In conclusion, the results show very similar effects of HU and SF on mouse soleus muscle, including activation of specific gene programs. The EDL muscle is able to counterbalance this latter, probably by activating compensatory mechanisms. The numerous effects of PTN on muscle gene expression and functional parameters demonstrate the sensitivity of muscle fibers to the cytokine. Although little benefit was found in HU muscle disuse, PTN may emerge useful in various muscle diseases, because it exerts synergetic actions on muscle fibers and vessels, which could enforce oxidative metabolism and ameliorate muscle performance.