Different incorporation of glucocorticoid hormone into diploid and tetraploid liver nuclei

Tetraploid parenchymal rat liver nuclei incorporate about twice as much (³H)dexamethasone as diploid parenchymal nuclei both in vivo and in vitro. This suggests that the ability of hepatic nuclei to incorporate glucocorticoid hormone is influenced by the number of copies of the genome in these nuclei.     

A mutation in the RNA polymerase β′ subunit causing depressed ribosomal RNA synthesis in Escherichia coli

Molecular Genetics and Genomics - Macromolecular synthesis in an Escherichia coli mutant with a temperature-sensitive β′ subunit of RNA polymerase was analysed. At the non-permissive...     

Effects of solubilization on the inhibition of the p-type ATPase from maize roots by N-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline

The biochemical events utilized by transport proteins to convert the chemical energy from the hydrolysis of ATP into an electro-chemical gradient are poorly understood. The inhibition of the plasma membrane ATPase from corn (Zea mays L.) roots by N-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline (EEDQ) was compared to that of ATPase solubilized with N-tetradecyl-N,N-dimethyl-3-ammonio-1-propane-sulfonate (3-14) to provide insight into the minimal functional unit. The chromatographic behavior of the 3-14-solubilized ATPase activity during size exclusion chromatography and glycerol gradient centrifugation indicated that the solubilized enzyme was in a monomeric form. Both plasma membrane-bound and solubilized ATPase were inhibited by EEDQ in a time- and concentration-dependent manner consistent with a first-order reaction. When the log of the reciprocal of the half-time for inhibition was plotted as a function of the log of the EEDQ concentration, straight lines were obtained with slopes of approximately 0.5 and 1.0 for membrane-bound and 3-14-solubilized ATPase, respectively, indicating a change in the number of polypeptides per functional ATPase complex induced by solubilization with 3-14.     

Effects of pH on proton transport by vacuolar pumps from maize roots

Protons pumps of the tonoplast may be involved in the regulation of cytosolic pH, but the effects of pH on the coupled activities of these transporters are poorly understood. The effects of pH on the activities of the H⁺-translocating pyrophosphatase (PP_iase) and vacuolar-type H⁺-translocating adenosine triphosphatase (H⁺-ATPase) from maize ( Zea mays L. cv. FRB 73) root membranes were assessed by model that simultaneously considers proton transport by the pump and those processes that reduce net transport. The addition of either pyrophosphate or ATP to either microsomal or tonoplast membranes generated a pH gradient. The pH gradient generated in the presence of both substrates was not the sum of the gradients produced by the two substrates added separately. When membranes were separated by sucrose density gradient centrifugation, pyrophosphate (PP_i)-dependent proton transport was associated with light density membranes having tonoplast H⁺-ATPase activity. These results indicate that some portion of the PP_iase was located on the same membrane system as the tonoplast ATPase; however, tonoplast vesicles may be heterogeneous, differing slightly in the ratio of ATP- to PP_i-dependent transport. Proton transport by both the PP_iase and ATPase had maximal activity at pH 7.0 to 8.0 Decreases in proton transport by the ATPase at pH above the optimum were associated with increases in the processes that reduce net transport. Such an association was not observed at pH values below the optimum. These results are discussed in terms of in situ regulation of cytoplasmic pH by the two pumps.     

Metabolism of trans-Aconitic Acid in Maize : II. Regulatory Properties of Two Compartmented Forms of Citrate Dehydrase

Kinetics of two molecular forms of K-dependent citrate dehydrase in maize (Zea mays L.) are reported. The isozymes, designated CD I and CD II, were found to be compartmented in mitochondria and cytosol, respectively.

CD I exhibited hyperbolic kinetics with respect to both citrate and potassium with K_m 2.3 and 12 millimolar, respectively. Maximum velocity was 0.38 micromole of trans-aconitic acid per minute per milligram protein. The pH optimum was 7.2. trans-aconitic synthesis by CD I is regulated by both citrate concentration and pH.

CD II exhibited hyperbolic kinetics with respect to citrate (K_m 0.6 millimolar) but sigmoidal kinetics with respect to potassium. trans-aconitic acid synthesis by CD II is regulated by potassium. This may account for the positive correlation between leaf potassium and trans-aconitic acid in certain grasses (Clark 1968 Crop Sci 8: 165).

     

The influence of conductivity changes in boundary element compartments on the forward and inverse problem in electroencephalography and magnetoencephalography.

Source localization based on magnetoencephalographic and electroencephalographic data requires knowledge of the conductivity values of the head. The aim of this paper is to examine the influence of compartment conductivity changes on the neuromagnetic field and the electric scalp potential for the widely used three compartment boundary element models. Both the analysis of measurement data and the simulations with dipoles distributed in the brain produced two significant results. First, we found the electric potentials to be approximately one order of magnitude more sensitive to conductivity changes than the magnetic fields. This was valid for the field and potential topology (and hence dipole localization), and for the amplitude (and hence dipole strength). Second, changes in brain compartment conductivity yield the lowest change in the electric potentials topology (and hence dipole localization), but a very strong change in the amplitude (and hence in the dipole strength). We conclude that for the magnetic fields the influence of compartment conductivity changes is not important in terms of dipole localization and strength estimation. For the electric potentials however, both dipole localization and strength estimation are significantly influenced by the compartment conductivity.     

The role of ultrasonic bat detectors in improving inventory and monitoring surveys in Vietnamese karst bat assemblages

Bats account for 30% of mammal diversity in SE Asia and are potential bioindicators of wider biodiversity impacts resulting from habitat loss and climate change.As existing sampling techniques in the region typically fail to record bats that habitually fly in open areas and at higher altitudes,current inventory efforts are less than comprehensive.Acoustic sampling with bat detectors may help to overcome these limitations for insectivorous bats,but has yet to be tested in mainland SE Asia.To do so,we sampled...     

Modelling strategies for controlling SARS outbreaks

Severe acute respiratory syndrome (SARS), a new, highly contagious, viral disease, emerged in China late in 2002 and quickly spread to 32 countries and regions causing in excess of 774 deaths and 8098 infections worldwide. In the absence of a rapid diagnostic test, therapy or vaccine, isolation of individuals diagnosed with SARS and quarantine of individuals feared exposed to SARS virus were used to control the spread of infection. We examine mathematically the impact of isolation and quarantine on the control of SARS during the outbreaks in Toronto, Hong Kong, Singapore and Beijing using a deterministic model that closely mimics the data for cumulative infected cases and SARS-related deaths in the first three regions but not in Beijing until mid-April, when China started to report data more accurately. The results reveal that achieving a reduction in the contact rate between susceptible and diseased individuals by isolating the latter is a critically important strategy that can control SARS outbreaks with or without quarantine. An optimal isolation programme entails timely implementation under stringent hygienic precautions defined by a critical threshold value. Values below this threshold lead to control, but those above are associated with the incidence of new community outbreaks or nosocomial infections, a known cause for the spread of SARS in each region. Allocation of resources to implement optimal isolation is more effective than to implement sub-optimal isolation and quarantine together. A community-wide eradication of SARS is feasible if optimal isolation is combined with a highly effective screening programme at the points of entry.     

Quantification of the magnification and distortion effects of a pediatric flexible video-bronchoscope

Background

Flexible video bronchoscopes, in particular the Olympus BF Type 3C160, are commonly used in pediatric respiratory medicine. There is no data on the magnification and distortion effects of these bronchoscopes yet important clinical decisions are made from the images. The aim of this study was to systematically describe the magnification and distortion of flexible bronchoscope images taken at various distances from the object.

Methods

Using images of known objects and processing these by digital video and computer programs both magnification and distortion scales were derived.

Results

Magnification changes as a linear function between 100 mm (×1) and 10 mm (×9.55) and then as an exponential function between 10 mm and 3 mm (×40) from the object. Magnification depends on the axis of orientation of the object to the optic axis or geometrical axis of the bronchoscope. Magnification also varies across the field of view with the central magnification being 39% greater than at the periphery of the field of view at 15 mm from the object. However, in the paediatric situation the diameter of the orifices is usually less than 10 mm and thus this limits the exposure to these peripheral limits of magnification reduction. Intraclass correlations for measurements and repeatability studies between instruments are very high, r = 0.96. Distortion occurs as both barrel and geometric types but both types are heterogeneous across the field of view. Distortion of geometric type ranges up to 30% at 3 mm from the object but may be as low as 5% depending on the position of the object in relation to the optic axis.

Conclusion

We conclude that the optimal working distance range is between 40 and 10 mm from the object. However the clinician should be cognisant of both variations in magnification and distortion in clinical judgements.