Binding of radioactively labeled carboxyatractyloside, atractyloside and bongkrekic acid to the ADP translocator of potato mitochondria

1. The inhibition of the ADP-stimulated respiration of potato mitochondria by carboxyatractyloside is relieved by high concentration of ADP or by the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). Atractyloside is a much less potent inhibitor than carboxyatractyloside. The inhibition of the ADP-stimulated respiration required about 60-times more atractyloside than carboxyatractyloside. 2. [35S]carboxyatractyloside and [3H]bongkrekic acid bind to potato mitochondria with high affinity (Kd = 10 to 20 nM, n=0.6-0.7 nmol per mg protein). Added ADP competes with carboxyatractyloside for binding; on the contrary ADP increases the amount of bound bongkrekic acid. [3H]atractyloside binds to potato mitochondria with a much lower affinity (Kd=0.45 muM) than carboxyatractyloside or bongkrekic acid. 3. Bound [3H]atractyloside is displaced by ADP, carboxyatractyloside and bongkrekic acid. The displacement of bound [35S]carboxyatractyloside by bongkrekic acid and of bound [3H]bongkrekic acid by carboxyatractyloside is markedly increased by ADP. 4. Bongkrekic acid competes with [35S]carboxyatractyloside for binding. Addition of a small concentration of ADP considerably enhances the inhibitory effect of bongkrekic acid on [35S]carboxyatractyloside binding. 5. The adenine nucleotide content of potato mitochondria is of the order of 1 nmol per mg protein. ADP transport in potato mitochondria is inhibited by atractyloside 30- to 40-times less efficiently than by carboxyatractyloside.     

Local entropy generation and entropy fluxes of a transient flame during head-on quenching towards solid and hydrogen-permeable porous walls

Premixed H₂-air flames are studied in a one-dimensional wall-bounded configuration. The laminar flame propagates towards and quenches at a wall that is either solid or permeable. Entropy generation by each of 19 elementary reactions is evaluated. Their total contribution remains the most important up to the quenching instance. Close to quenching, the conduction entropy generation grows considerable. Mass diffusion has a modest contribution, which decreases towards quenching. Viscous forces are negligible as a source of entropy. Effects of unburnt-mixture temperature and fuel-air ratio are investigated, and also dilution with nitrogen (inert) and water vapour. The diffusive entropy flux changed direction away from the permeating wall compared that of the solid wall. A major finding is that fuel permeation through the wall tends to decrease the entropy generation per unit of converted fuel, in particular for initially lean mixtures.     

New features of 23S ribosomal RNA folding: the long helix 41-42 makes a "U-turn" inside the ribosome

23S rRNA from Escherichia coli was cleaved at single internucleotide bonds using ribonuclease H in the presence of appropriate chimeric oligonucleotides; the individual cleavage sites were between residues 384 and 385, 867 and 868, 1045 and 1046, and 2510 and 2511, with an additional fortuitous cleavage at positions 1117 and 1118. In each case, the 3' terminus of the 5' fragment was ligated to radioactively labeled 4-thiouridine 5'-,3'-biphosphate ("psUp"), and the cleaved 23S rRNA carrying this label was reconstituted into 50S subunits. The 50S subunits were able to associate normally with 30S subunits to form 70S ribosomes. Intra-RNA crosslinks from the 4-thiouridine residues were induced by irradiation at 350 nm, and the crosslink sites within the 23S rRNA were analyzed. The rRNA molecules carrying psUp at positions 867 and 1117 showed crosslinks to nearby positions on the opposite strand of the same double helix where the cleavage was located, and no crosslinking was detected from position 2510. In contrast, the rRNA carrying psUp at position 384 showed crosslinking to nt 420 (and sometimes also to 416 and 425) in the neighboring helix in 23S rRNA, and the rRNA with psUp at position 1045 gave a crosslink to residue 993. The latter crosslink demonstrates that the long helix 41-42 of the 23S rRNA (which carries the region associated with GTPase activity) must double back on itself, forming a "U-turn" in the ribosome. This result is discussed in terms of the topography of the GTPase region in the 50S subunit, and its relation to the locations of the 5S rRNA and the peptidyl transferase center.     

Prevention of heart failure]

Heart failure is a major problem of public health, associated with poor outcome in the advanced stage, thus justifying its prevention. Primary prevention is based on the prevention and treatment of its principal etiologic factors, hypertension and coronary artery disease. Broad use of echocardiography or dosage of neurohormonal markers improve detection of asymptomatic left ventricular dysfunction. In ischemic heart disease, coronary recanalisation prevents or limits left ventricular remodeling and dysfunction, even if the "open artery" theory has not been entirely proved. Understanding the deleterous role of neurohormonal stimulation results in a large use of ACE-inhibitors, which beneficial effect has been demonstrated also in case of asymptomatic left ventricular dysfunction. Betablockers, already largely used after myocardial infarction, seem to have also a beneficial effect in heart failure: the same is probably also true for angiotensin II-antagonists. Double blocking of both the sympathetic nervous system and the angiotensin-aldosterone system seems to be recommended. More precisely understanding the pathways signaling the processes of ventricular remodeling and dysfunction points to new potential targets for a preventive treatment: endothelin receptors, apoptosis, oxidative stress, cytokines or even angiogenesis.     

The weld pool region of welded cast metal-matrix ceramic-particulate composites

The successful application of ceramic-particulate reinforced metal matrix composites as engineering materials requires that they be amenable to fabrication by joining processes such as welding. In such a case, the weld pool would undergo intense agitation during welding and the ceramic particulates would tend to segregate, causing deterioration in the mechanical and wear properties of the joined portion. In the present work, a thermo-physical model has been used to predict the velocities of fluid movement in the weld pool as a function of heat input. An attempt has been made to combine analytical and numerical methods in order to ensure the accuracy of the model's predictions and at the same time to make the computation faster. Aluminium-alumina and aluminum-silicon carbide composites were prepared by casting and the resultant plates of standard dimensions and thicknesses were welded using the MIG process. The distribution of the ceramic particulates and their reaction with the matrix in the welded zone were determined using metallographic and SEM techniques. The distribution was then simulated from the fluid flow velocities obtained by the model developed by the authors. A good correlation was seen between the intensity of molten metal velocities and the particle distribution. Particle pushing and engulfment by the solidifying melt interface also appeared to be affecting the particle distribution in the weld zone.