Molecular dynamics simulations of the docking of substituted N5- deazapterins to dihydrofolate reductase

Orientations of the deazapterin ring and the conformational preferences of groups appended to the deazapterin ring in a set of 8-substituted deazapterin cations docked into the dihydrofolate reductase (DHFR) binding site have been investigated using a methodology based on the simulated annealing technique within molecular dynamics (MD) simulations. Of five possible binding pockets for the 8-substituents, identified from a preliminary manual docking study, one has been definitively eliminated after an analysis of MD trajectories, while another remains uncertain. Using a new method based on standard thermodynamic cycles and a linear approximation of polar and non-polar free energy contributions from MD averages, binding affinities of the different ligands in each binding site have been correlated with experimental dissociation constants. The study has provided insights into structure-activity relationships for use in the design of modified inhibitors of DHFR.      

The influence of mechanical factors in alternating-current collector machines on level of radio noise

The influence of the mechanical state of the brush-collector contact on the level of radio noise in alternating-current collector machines is considered. Two methods to reduce the level of radio noise are offered: via a shift of current-carrying brush holders with respect to the radial position in the direction of rotation by half of the tangential size of the brush and application of lubricating brushes made on the basis of molybdenum disulfide.     

Stress corrosion cracking of zirconium cladding tubes: I. Proximate local SCC testing method

The mechanisms and kinetics of corrosion fracture of thin-wall cladding tubes of zirconium alloys in a methanol-iodine medium are determined by a direct comparison of the acoustic emission parameters with the characteristics of accumulated corrosion defects in a material during stress corrosion cracking tests. The main types of corrosion defects (nucleation, development, interaction) are revealed and quantitatively described. A general sequence of nucleation and development of corrosion defects is established for all types of tubes.     

Regulation of synaptic position, size, and strength in anuran skeletal muscle

An analysis of the physiology, morphology, and position of endplates on identified fibers in the Xenopus laevis pectoralis muscle has revealed the following. 1. The percentage of fibers with one endplate is lower in large muscles, and within the same muscle, singly innervated fibers are smaller than dually innervated fibers. 2. Single junctions tend to be stronger than junctions on dually innervated fibers. 3. Single junctions typically are located near the middle of their fibers, while the endplates on dually innervated fibers are located toward either end and usually are separated by at least 20% of the total fiber length. A significant proportion of dually innervated fibers appears to be innervated by the same axon at both junctions. 4. Junctions on the same dually innervated fiber tend to be more similar in length than do junctions on different fibers of the same input resistance. This observation is the same whether both junctions on a given fiber are formed by the same or different axons. There is no corresponding tendency for greater similarity in physiological strength of paired junctions, which frequently show large differences in endplate potential amplitude. 5. The total terminal length on dually innervated fibers of equivalent input resistance is inversely correlated with the mean release per unit length and total release of both junctions. There is no apparent correlation between the distance separating endplates and their strength or length. The data support a model of synaptic regulation in which nerve terminals are attracted, grow, and are maintained in proportion to the amount of a substance supplied by muscle fibers. Our findings suggest that such a substance is produced or distributed uniformly throughout each fiber in amounts proportional to the fiber size and inversely proportional to the total transmitter output of all junctions innervating the fiber. A form of competitive interaction between the terminals which helps to determine synaptic spacing may involve local depletion or inactivation of this substance.     

An examination of the reactive sputtering of silicon nitride on to gallium arsenide

The deposition of silicon nitride thin films by the reactive sputtering of elemental silicon in a nitrogen/argon plasma has been investigated. The composition of the thin films has been examined using infra-red reflectance, X-ray photoelectron and Auger electron spectroscopies and spark source mass spectrometry. Oxygen has been found to be a major contaminant in these sputter deposited films, the oxygen concentration depending on the ambient gas pressure. The use of the silicon oxy-nitride films as annealing encapsulants for the activation of silicon ion implanted semi-insulating gallium arsenide has also been investigated.     

Radiative recombination rate coefficients for highly-charged tungsten ions

Partial and total radiative recombination rate coefficients are presented for highly-charged ions of tungsten with closed shells, W²⁸⁺, W³⁸⁺, W⁴⁶⁺, W⁵⁶⁺, W⁶⁴⁺, W⁷⁰⁺, and W⁷²⁺, as well as for the H-like ion W⁷³⁺ and the bare nucleus W⁷⁴⁺. The temperature range is considered. Calculations have been performed in the framework of the fully relativistic Dirac-Fock treatment of photoionization and radiative recombination processes taking into account all significant multipoles of the radiation field. We assess the influence of multipole effects on recombination rate coefficients as compared with the commonly used dipole approximation. For the first time, we show that the relativistic Maxwell-Boltzmann distribution of continuum electrons should be used at high temperature. This decreases the rate coefficient significantly compared to the nonrelativistic distribution.     

Aurothioglucose inhibits murine thioredoxin reductase activity in vivo

Gold (I)-containing compounds, including aurothioglucose (ATG), are potent in vitro inhibitors of several selenocysteine-containing enzymes. Gold compounds have also been shown to potentiate the virulence of several viruses in mice, including coxsackievirus, implicated as a possible infectious agent in Keshan disease. One possible mechanism by which gold compounds may be increasing the virulence of viral infections in mice is by acting as a selenium antagonist in vivo and inducing oxidative stress. To investigate the possible role of gold compounds in inducing oxidative stress in mice, we assessed the ability of ATG administered in vivo to inhibit the activity of the selenocysteine-containing enzymes thioredoxin reductase (TR) and glutathione peroxidase (GPX1). Doses as low as 0. 025 mg ATG/g body weight caused significant and prolonged inhibition of TR activity in all tissues examined. No such inhibition of GPX1 activity was seen, indicating differential in vivo sensitivity of the enzymes to inhibition by ATG. In liver and heart, some recovery of TR activity was observed after a 7-d period, but no recovery was observed in pancreas or kidney. Because TR is involved in several important cellular redox functions, its inhibition most likely will affect multiple cellular processes. These results indicate that in vivo administration of ATG results in significant and long-lasting inhibition of TR activity. Such inhibition of TR could lead to increased levels of oxidative stress in vivo, thereby increasing the virulence of several viruses including the coxsackievirus.     

Stimulation of the extracellular signal-regulated kinase 1/2 pathway by human beta-3 adrenergic receptor: new pharmacological profile and mechanism of activation

(-)Deprenyl is an irreversible inhibitor of monoamine oxidase B (MAO-B) frequently used as an adjunct therapy in the treatment of Parkinson's Disease. Recent evidence, however, has found that deprenyl's metabolites are associated with an antiapoptotic action within certain neuronal populations. Interestingly, deprenyl's antiapoptotic actions appear not to depend upon the inhibition of MAO-B. Due to a paucity of information surrounding (-)deprenyl's ability to spare neurons in vivo, a series of studies was conducted to further investigate this phenomenon within an apoptotic neuronal death model: kainic acid induced excitotoxicity. Results indicated that (-)deprenyl increased hippocampal neuronal survival compared to saline-matched controls following kainic acid insult. Furthermore, it was discovered that (-)deprenyl treatment could be stopped 14 days following CNS insult by kainate, with evidence of neuronal sparing still present by day 28. In open-field locomotor activity testing of kainate-treated animals, those given subsequent (-)deprenyl treatment showed habituation curves similar to control subjects, while saline-treated animals did not. Given deprenyl's antiapoptotic actions, it is proposed that (-)deprenyl may be beneficial in the treatment of a variety of neurodegenerative diseases where evidence of apoptosis exists, such as Parkinson's and Alzheimer's Disease, by slowing the disease process itself.