Habitual physical activity in daily life correlates positively with markers for mitochondrial capacity.

Physical exercise training is a powerful tool to maintain or improve mitochondrial density and function (mitochondrial capacity). This study aims to determine whether mitochondrial capacity is also associated with habitual physical activity in daily life (PADL). The capacity of classic markers for mitochondrial density, i.e., the capacity of citrate synthase (CS) and succinate dehydrogenase (SDH), as well the capacity of cytochrome c oxidase (COX) and beta-hydroxyacyl-CoA dehydrogenase (HAD), was determined in homogenized muscle biopsy samples obtained from the vastus lateralis muscle of nonexercising healthy young (age 20+/-2 yr) subjects (31 women, 7 men). PADL was measured during two periods of 14 days using a triaxial accelerometer for movement registration. CS, SDH, and COX were positively associated with PADL [P<0.05, R=0.36, 95% confidence interval (CI): 1.3.10(-4) to 2.2.10(-3); P<0.05, R=0.39, 95% CI: 1.1.10(-5) to 9.9.10(-5); and P<0.05, R=0.33, 95% CI: 7.5.10(-6) to 3.6.10(-4), respectively], and HAD tended to correlate positively with PADL (P=0.06, R=0.31, 95% CI: -2.2.10(-5) to 1.1.10(-3)). The population was subsequently stratified based on the intensity of the activities performed. CS was only associated with PADL in subjects spending more time on high-intensity physical activity, whereas HAD was only associated with PADL in subjects spending less time on low intensity physical activity. We are the first to report that even within the range of normal daily life activities, mitochondrial capacity is positively associated with the level of habitual physical activity in daily life. Thus an active lifestyle may help to maintain or improve mitochondrial capacity.     

H/D exchange mass spectrometry and statistical coupling analysis reveal a role for allostery in a ferredoxin-dependent bifurcating transhydrogenase catalytic cycle

Recent investigations into ferredoxin-dependent transhydrogenases, a class of enzymes responsible for electron transport, have highlighted the biological importance of flavin-based electron bifurcation (FBEB). FBEB generates biomolecules with very low reduction potential by coupling the oxidation of an electron donor with intermediate potential to the reduction of high and low potential molecules. Bifurcating systems can generate biomolecules with very low reduction potentials, such as reduced ferredoxin (Fd), from species such as NADPH. Metabolic systems that use bifurcation are more efficient and confer a competitive advantage for the organisms that harbor them. Structural models are now available for two NADH-dependent ferredoxin-NADP⁺ oxidoreductase (Nfn) complexes. These models, together with spectroscopic studies, have provided considerable insight into the catalytic process of FBEB. However, much about the mechanism and regulation of these multi-subunit proteins remains unclear. Using hydrogen/deuterium exchange mass spectrometry (HDX-MS) and statistical coupling analysis (SCA), we identified specific pathways of communication within the model FBEB system, Nfn from Pyrococus furiosus, under conditions at each step of the catalytic cycle. HDX-MS revealed evidence for allosteric coupling across protein subunits upon nucleotide and ferredoxin binding. SCA uncovered a network of co-evolving residues that can provide connectivity across the complex. Together, the HDX-MS and SCA data show that protein allostery occurs across the ensemble of iron?sulfur cofactors and ligand binding sites using specific pathways that connect domains allowing them to function as dynamically coordinated units.     

Effects of calcium manipulation and glucose stimulation on a histochemically detectable mobile calcium fraction in isolated rat pancreatic islets

Summary Pancreatic B-cell calcium as histochemically detectable with glyoxal bis (2-hydroxyanil)=GBHA was studied in isolated islets of fed rats. GBHA has previously been shown by us to detect an ionized or readily ionizable Ca-fraction (GBHA-Ca). In the presence of Ca⁺⁺ (2.5 mM), high glucose (15 mM) induced a rapid decrease (30%) of islet GBHA-Ca followed by a rise between 30 and 60 min to levels above the initial value. At low glucose (0 or 2.5 mM) GBHA-Ca showed a slight and gradual decline under these conditions. Omission of Ca⁺⁺ at low glucose rapidly decreased (30%) islet GBHA-Ca. This decrease was markedly inhibited by high glucose, although glucose did not induce insulin secretion under these conditions. Preincubation in the absence of Ca⁺⁺ (15 min) depleted islet GBHA-Ca, but partial restoration occurred during subsequent incubation with Ca⁺⁺ at low glucose. By contrast, high glucose completely restored GBHA-Ca within 5 min, followed by a decline and a subsequent rise. Reintroduction of Ca⁺⁺ also rapidly restored the glucose-induced insulin secretion. These results indicate that islet GBHA-Ca represents a mobile Ca-fraction which is dependent on extracellular Ca⁺⁺ and which responds very rapidly to glucose stimulation. It is suggested that changes of GBHA-Ca in the B-cells may reflect changes in the Ca pool involved in the insulin secretory mechanism.     

Continuous-time Markov chains as models for animal behaviour

A survey is given of the application of (functions of) continuous-time Markov chains in the statistical analysis of behavioural time series.     

A new mechanism for reduced sensitivity to demethylation‐inhibitor fungicides in the fungal banana black Sigatoka pathogen Pseudocercospora fijiensis

The Dothideomycete Pseudocercospora fijiensis, previously Mycosphaerella fijiensis, is the causal agent of black Sigatoka, one of the most destructive diseases of bananas and plantains. Disease management depends on fungicide applications, with a major contribution from sterol demethylation‐inhibitors (DMIs). The continued use of DMIs places considerable selection pressure on natural P. fijiensis populations, enabling the selection of novel genotypes with reduced sensitivity. The hitherto explanatory mechanism for this reduced sensitivity was the presence of non‐synonymous point mutations in the target gene Pfcyp51, encoding the sterol 14α‐demethylase enzyme. Here, we demonstrate a second mechanism involved in DMI sensitivity of P. fijiensis. We identified a 19‐bp element in the wild‐type (wt) Pfcyp51 promoter that concatenates in strains with reduced DMI sensitivity. A polymerase chain reaction (PCR) assay identified up to six Pfcyp51 promoter repeats in four field populations of P. fijiensis in Costa Rica. We used transformation experiments to swap the wt promoter of a sensitive field isolate with a promoter from a strain with reduced DMI sensitivity that comprised multiple insertions. Comparative in vivo phenotyping showed a functional and proportional up‐regulation of Pfcyp51, which consequently decreased DMI sensitivity. Our data demonstrate that point mutations in the Pfcyp51 coding domain, as well as promoter inserts, contribute to the reduced DMI sensitivity of P. fijiensis. These results provide new insights into the importance of the appropriate use of DMIs and the need for the discovery of new molecules for black Sigatoka management.     

Phloem exudate metabolic content reflects the response to water-deficit stress in pea plants (Pisum sativum L.)

Drought stress impacts the quality and yield of Pisum sativum. Here, we show how short periods of limited water availability during the vegetative stage of pea alters phloem sap content and how these changes are connected to strategies used by plants to cope with water deficit. We have investigated the metabolic content of phloem sap exudates and explored how this reflects P. sativum physiological and developmental responses to drought. Our data show that drought is accompanied by phloem-mediated redirection of the components that are necessary for cellular respiration and the proper maintenance of carbon/nitrogen balance during stress. The metabolic content of phloem sap reveals a shift from anabolic to catabolic processes as well as the developmental plasticity of P. sativum plants subjected to drought. Our study underlines the importance of phloem-mediated transport for plant adaptation to unfavourable environmental conditions. We also show that phloem exudate analysis can be used as a useful proxy to study stress responses in plants. We propose that the decrease in oleic acid content within phloem sap could be considered as a potential marker of early signalling events mediating drought response.     

Local and global cycles in an acarine predator-prey system: a frequency domain analysis

Techniques of time series analysis are applied to the dynamics of the phytophagous miteTetranychus urticae Koch and its predatorTyphlodromus occidentalis Nesbitt in six experimental mini-orchards, sampled weekly during two years (van de Klashorst et al., 1992). Autocovariance and crosscovariance functions characterize local and global behaviour in the time domain. Spectral density function and cross amplitude spectrum provide important information of the system's behaviour in the frequency domain. Because of a strikingly different behaviour, the total record was cut into two distinct periods. During the first period, all local systems oscillate with a frequency of four cycles per year and all in phase, resulting in a strongly periodical global behaviour at a high mean level. Since the mean local power spectra coincide with the global power spectrum over a wide range of frequencies, it is concluded that the total system of six orchards is homogeneous. During the second period, all local power spectra are mutually different, more or less smoothed with no apparent peak pointing to a periodical component. The resulting global power spectrum is almost flat at a low mean level. The system is heterogeneous with a quasi-stable global behaviour.From the cross-amplitude spectrum it became clear that the dynamics of the two species within the orchards remained strongly coupled over a wide range of frequencies.Since the experimental circumstances had not been intentionally changed, the origin of the drastic change in behaviour could not be identified. If high rates of dispersal have been the synchronizer during the first period, it is not clear why asynchrony suddenly occured in the second period.A comparison of the overall record with the results of Nachman's (1987) stochastic simulation model suggests that the change could possibly be of stochastic origin.     

In vivo fate of large unilamellar sphingomyelin-cholesterol liposomes after intraperitoneal and intravenous injection into rats

We investigated the fate of intraperitoneally and intravenously injected reverse phase evaporation vesicles of fairly uniform size (100–200 m) with respect to blood celarance, tissue distribution and integrity in vivo. The vesicles are composed of sphingomyelin and cholesterol in a molar ratio 3 : 2 and contain ¹²⁵I-labeled poly(vinyl pyrrolidone) in the aqueous compartment. It is shown that following an intrapersoneal injection the vesicles are transported intact, and not associated with cells, from the peritoneal activity to the blood and are subsequently taken up mainly by liver and spleen, where, particularly in liver, the phospholipid is partially metabolized. After an intraperitoneal injection the rate of vesicle-uptake by liver and spleen is reduced by a factor of 2–3 compared to the rate of vesicle-uptake by liver and spleen following an intravenous injection. The peritoneal cavity functions as a reservior of vesicles for some hours. The rates of blood clearance and uptake of the vesicles by liver and spleen appear to be slower than that found for vesicles of different lipid composition.