643 research outputs found
Work probability distribution in single molecule experiments
We derive and solve a differential equation satisfied by the probability
distribution of the work done on a single biomolecule in a mechanical unzipping
experiment. The unzipping is described as a thermally activated escape process
in an energy landscape. The Jarzynski equality is recovered as an identity,
independent of the pulling protocol. This approach allows one to evaluate
easily, by numerical integration, the work distribution, once a few parameters
of the energy landscape are known.Comment: To appear on EP
An Ising-Like model for protein mechanical unfolding
The mechanical unfolding of proteins is investigated by extending the
Wako-Saito-Munoz-Eaton model, a simplified protein model with binary degrees of
freedom, which has proved successful in describing the kinetics of protein
folding. Such a model is generalized by including the effect of an external
force, and its thermodynamics turns out to be exactly solvable. We consider two
molecules, the 27th immunoglobulin domain of titin and protein PIN1. In the
case of titin we determine equilibrium force-extension curves and study
nonequilibrium phenomena in the frameworks of dynamic loading and force clamp
protocols, verifying theoretical laws and finding the position of the kinetic
barrier which hinders the unfolding of the molecule. The PIN1 molecule is used
to check the possibility of computing the free energy landscape as a function
of the molecule length by means of an extended form of the Jarzynski equality.Comment: 4 pages + appendi
A Change in the Radius of Rotation of F1-ATPase Indicates a Tilting Motion of the Central Shaft
AbstractF1-ATPase is a water-soluble portion of FoF1-ATP synthase and rotary molecular motor that exhibits reversibility in chemical reactions. The rotational motion of the shaft subunit γ has been carefully scrutinized in previous studies, but a tilting motion of the shaft has never been explicitly postulated. Here we found a change in the radius of rotation of the probe attached to the shaft subunit γ between two different intermediate states in ATP hydrolysis: one waiting for ATP binding, and the other waiting for ATP hydrolysis and/or subsequent product release. Analysis of this radial difference indicates a ∼4° outward tilting of the γ-subunit induced by ATP binding. The tilt angle is a new parameter, to our knowledge, representing the motion of the γ-subunit and provides a new constraint condition of the ATP-waiting conformation of F1-ATPase, which has not been determined as an atomic structure from x-ray crystallography
Estilos de liderazgo y productividad del personal de la gerencia regional forestal y de fauna silvestre de Madre de Dios
La tesis intitulada “Estilos de Liderazgo y su Relación con la Productividad del
Personal de la Gerencia Regional Forestal y de Fauna Silvestre de Madre de
Dios, 2022”, tenía como objetivo determinar cómo los estilos de liderazgo se
relacionan con la productividad del personal de la Gerencia Regional Forestal
y de Fauna Silvestre de Madre de Dios, 2022; la muestra fue censal, por
cuanto se trabajó con el total de la población, es decir con los 38 trabajadores
de la institución, el tipo y diseño de la tesis fue descriptivo correlacional de
corte transversal. Los instrumentos empleados tuvieron 48 ítems, en estilos
de liderazgo tenía 28 ítems, productividad tenía 20 ítems, ambos con igual
escala Likert. La fiabilidad en ambos instrumentos tuvo “Buena Confiabilidad”
por cuanto el coeficiente de Alfa de Cronbach, en estilos de liderazgo fue
0.801 y en productividad del personal 0.830. El coeficiente de correlación de
las variables tuvo un valor de 0,946, expresando una correlación significativa,
el coeficiente de determinación R cuadrado 0,895, que indica el 89.50% de
los cambios observados en la variable productividad es debido a los cambios
de la variable estilos de liderazgo
Internal Motility in Stiffening Actin-Myosin Networks
We present a study on filamentous actin solutions containing heavy meromyosin
subfragments of myosin II motor molecules. We focus on the viscoelastic phase
behavior and internal dynamics of such networks during ATP depletion. Upon
simultaneously using micro-rheology and fluorescence microscopy as
complementary experimental tools, we find a sol-gel transition accompanied by a
sudden onset of directed filament motion. We interpret the sol-gel transition
in terms of myosin II enzymology, and suggest a "zipping" mechanism to explain
the filament motion in the vicinity of the sol-gel transition.Comment: 4 pages, 3 figure
Hyperbaric Oxygen Exposure Reduces Age-Related Decrease in Oxidative Capacity of the Tibialis Anterior Muscle in Mice
The effects of exposure to hyperbaric oxygen on the oxidative capacity of the skeletal muscles in mice at different ages were investigated. We exposed 5-, 34-, 55-, and 88-week-old mice to 36% oxygen at 950 mmHg for 6 hours per day for 2 weeks. The activities of succinate dehydrogenase (SDH), which is a mitochondrial marker enzyme, of the tibialis anterior muscle in hyperbaric mice were compared with those in age-matched mice under normobaric conditions (21% oxygen at 760 mmHg). Furthermore, the SDH activities of type IIA and type IIB fibers in the muscle were determined using quantitative histochemical analysis. The SDH activity of the muscle in normobaric mice decreased with age. Similar results were observed in both type IIA and type IIB fibers in the muscle. The decrease in the SDH activity of the muscle was reduced in hyperbaric mice at 57 and 90 weeks. The decreased SDH activities of type IIA and type IIB fibers were reduced in hyperbaric mice at 90 weeks and at 57 and 90 weeks, respectively. We conclude that exposure to hyperbaric oxygen used in this study reduces the age-related decrease in the oxidative capacity of skeletal muscles
Coupling of Rotation and Catalysis in F1-ATPase Revealed by Single-Molecule Imaging and Manipulation
SummaryF1-ATPase is a rotary molecular motor that proceeds in 120° steps, each driven by ATP hydrolysis. How the chemical reactions that occur in three catalytic sites are coupled to mechanical rotation is the central question. Here, we show by high-speed imaging of rotation in single molecules of F1 that phosphate release drives the last 40° of the 120° step, and that the 40° rotation accompanies reduction of the affinity for phosphate. We also show, by single-molecule imaging of a fluorescent ATP analog Cy3-ATP while F1 is forced to rotate slowly, that release of Cy3-ADP occurs at ∼240° after it is bound as Cy3-ATP at 0°. This and other results suggest that the affinity for ADP also decreases with rotation, and thus ADP release contributes part of energy for rotation. Together with previous results, the coupling scheme is now basically complete
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