Diurnal Oscillations of Gas Production and Effluxes (CO2 and CH4) in Cores from a Peat Bog

Peat cores (15 cm diam X 30 cm deep) from Ellergower Moss, New Galloway, Scotland were kept and monitored at constant temperature (10 ± 0.1ºC) for gas production using a 1.6 mm diam stainless steel probe fitted with a membrane inlet and connected to a quadrupole mass spectrometer. In the headspace, O₂, CO₂ and CH₄ (measured at m/z values 32, 44 and 15 respectively) showed diurnal fluctuations in low-intensity natural daylight and under a light-dark (LD, 12:12) regime. Over the first few cycles O₂ and CO₂ increased together in the dark and decreased in the light, whereas CH₄ showed variations in antiphase with the other two gases. CO₂ and CH₄ also showed diurnal oscillations at 15 cm depth, but these decreased together in the light whereas argon (m/z = 40) was not varying. A highly-damped free-run of the oscillations in gas concentrations at 15cm depth was evident for only 3 cycles in complete darkness and at constant temperature. This might suggest desynchronization between individual plants with different free-running periods. A hydrocarbon signal (m/z = 26) at 15 cm depth also showed diurnal cycles but out of phase with CO 2 and CH 4 . We postulate a circadian control of microbiological activities imposed by the vascular plants (Carex, Eriophorum, Molinia, Calluna, Erica). Under natural conditions the pronounced temperature sensitivity of CO₂ and CH₄ emission results in entrainment to daily temperature cycles. The amplitudes of the rhythms are greatest when temperature and light intensity changes are most pronounced, i.e. when the fluctuations in environmental factors are most potent as synchronizers (zeitgebers) and as masking factors.     

Deterioration of cerebral autoregulation during orthostatic stress: insights from the frequency domain

To determine whether dynamiccerebral autoregulation is impaired during orthostatic stress, cerebralblood flow (CBF) velocity in the middle cerebral artery (transcranialDoppler) and mean arterial pressure (MAP; Finapres) were measuredcontinuously in 12 healthy subjects during ramped maximal lower bodynegative pressure (LBNP) to presyncope. Velocity andpressure were averaged over 6-min periods of stable data at rest andduring LBNP to examine steady-state cerebral hemodynamics. Beat-to-beatvariability of velocity and pressure were quantified by a "variationindex" (oscillatory amplitude/steady-state mean value) and by powerspectral analysis. The dynamic relationship between changes in pressureand velocity was evaluated by the estimates of transfer and coherencefunction. The results of the study were as follows.Steady-state MAP remained relatively constant during LBNP, whereas CBFvelocity decreased progressively by 6, 15, and 21% at 30,40, and 50 mmHg LBNP, respectively(P < 0.05 compared withbaseline). At the maximal level of LBNP (30 s beforepresyncope) MAP decreased by 9.4% in association with a prominentreduction in velocity by 24% (P < 0.05 compared with baseline). The variation index of pressure increasedsignificantly from 3.8 ± 0.3% at baseline to 4.5 ± 0.6% at50 mmHg LBNP in association with an increase in the variation index of velocity from 6.0 ± 0.6 to 8.4 ± 0.7%(P < 0.05). Consistently, the low-(0.07-0.20 Hz) and high-frequency (0.20-0.30 Hz) power ofvariations in pressure and velocity increased significantly at highlevels of LBNP (P < 0.05) inassociation with an increase in transfer function gain (24% at50 mmHg, P < 0.05). We conclude that the damping effects ofautoregulation on variations in CBF velocity are diminishedduring orthostatic stress in association with substantial falls insteady-state CBF velocity. We suggest that these changes may contributein part to the development of presyncope.

     

Joining forces in the quest for orthologs

A report of the 24th International Conference on Yeast Genetics and Molecular Biology, Manchester, UK, 19-24 July 2009.     

Multiple mechanisms of membrane anchoring of Escherichia coli penicillin-binding proteins

Abstract: The major penicillin-binding proteins (PBPs) of Escherichia coli play vital roles in cell wall biosynthesis and are located in the inner membrane. The high M _r PBPs 1A, 1B, 2 and 3 are essential bifunctional transglycosylases/transpeptidases which are thought to be type II integral inner membrane proteins with their C-terminal enzymatic domains projecting into the periplasm. The low M _r PBP4 is a DD-carboxypeptidase/endopeptidase, whereas PBPs 5 and are DD-carboxypeptidases. All three low M _r , PBPs act in the modification of peptidoglycan to allow expansion of the sacculus and are thought to be periplasmic proteins attached with varying affinities to the inner membrane via C-terminal amphiphilic α-helices. It is possible that the PBPs and other inner membrane proteins form a peptidoglycan synthesizing complex to coordinate their activities.     

Masculinized dominant females in a cooperatively breeding species

The molecular mechanisms underlying complex social behaviours such as dominance are largely unknown. Studying the cooperatively breeding African cichlid Neolamprologus pulcher, we show that dominant females were similar to dominant males in dominance behaviour, high testosterone levels and brain arginine vasotocin expression (a neuropeptide involved in vertebrate territorial, reproductive and social behaviours) compared to subordinate helpers, but had lower levels of 11-ketotestosterone than males. Furthermore, brain gene expression profiles of dominant females were most similar to those of the males (independent of social rank). Dominant breeder females are masculinized at the molecular and hormonal level while being at the same time reproductively competent, suggesting a modular organization of molecular and endocrine functions, allowing for sex-specific regulation.     

Complex spatial distribution and dynamics of an abundant Escherichia coli outer membrane protein, LamB

Advanced techniques for observing protein localization in live bacteria show that the distributions are dynamic. For technical reasons, most such techniques have not been applied to outer membrane proteins in Gram-negative bacteria. We have developed two novel live-cell imaging techniques to observe the surface distribution of LamB, an abundant integral outer membrane protein in Escherichia coli responsible for maltose uptake and for attachment of bacteriophage lambda. Using fluorescently labelled bacteriophage lambda tails, we quantitatively described the spatial distribution and dynamic movement of LamB in the outer membrane. LamB accumulated in spiral patterns. The distribution depended on cell length and changed rapidly. The majority of the protein diffused along spirals extending across the cell body. Tracking single particles, we found that there are two populations of LamB--one shows very restricted diffusion and the other shows greater mobility. The presence of two populations recalls the partitioning of eukaryotic membrane proteins between 'mobile' and 'immobile' populations. In this study, we have demonstrated that LamB moves along the bacterial surface and that these movements are restricted by an underlying dynamic spiral pattern.     

CC chemokine receptor-3 (CCR3) antagonists: improving the selectivity of DPC168 by reducing central ring lipophilicity

DPC168, a benzylpiperidine-substituted aryl urea CCR3 antagonist evaluated in clinical trials, was a relatively potent inhibitor of the 2D6 isoform of cytochrome P-450 (CYP2D6). Replacement of the cyclohexyl central ring with saturated heterocycles provided potent CCR3 antagonists with improved selectivity against CYP2D6. The favorable preclinical profile of DPC168 was maintained in an acetylpiperidine derivative, BMS-570520.