Biophysical Reviews and Letters

The effects of external torque on the F₁-ATPase rotary molecular motor are studied from the viewpoint of recent advances in stochastic thermodynamics. This motor is modeled in terms of discrete-state and continuous-state stochastic processes. The dependence of the discrete-state description on external torque and friction is obtained by fitting its transition rates to a continuous-angle model based on Newtonian mechanics with Langevin fluctuating forces and reproducing experimental data on this motor. In this approach, the continuous-angle model is coarse-grained into discrete states separated by both mechanical and chemical transitions. The resulting discrete-state model allows us to identify the regime of tight chemomechanical coupling of the F₁ motor and to infer that its chemical and mechanical efficiencies may reach values close to the thermodynamically allowed maxima near the stalling torque. We also show that, under physiological conditions, the F₁ motor is functioning in a highly-nonlinear-response regime, providing a rotation rate a million times faster than would be possible in the linear-response regime of nonequilibrium thermodynamics. Furthermore, the counting statistics of fluctuations can be obtained in the tight-coupling regime thanks to the discrete-state stochastic process and we demonstrate that the so-called fluctuation theorem provides a useful method for measuring the thermodynamic forces driving the motor out of equilibrium.

The interaction of propofol and human serum albumin (HSA) has been investigated by UV-absorption, fluorescence spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. Propofol has shown a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The binding constant (k) is estimated at a low value of 2.55 × 10³ M^-1 at 293 K. FT-IR spectroscopy with Fourier self-deconvolution technique was used to determine the protein secondary structure in the amide regions I, II and III. The observed spectral changes of HSA-propofol complex indicate a larger intensity decrease in the absorption band of α-helix relative to that of β-sheets. This variation in intensity is related indirectly to the formation of H-bonding in the complex molecules, which accounts for the different intrinsic propensities of α-helix and β-sheets.

In this paper, novel nonlinear statistical methods of immunofluorescence analysis are presented. We investigated the experimental data of DNA fluorescence in neutrophils nuclei of peripheral blood. DNA fluorescence is triggered by biochemical reactions of respiratory oxidative burst. Histograms of photon counts statistics are generated by flow cytometry method. The histograms represent distributions of fluorescence flash frequency as functions of fluorescence intensity. Large-scale averaging of initial histograms gives bifurcations of immunofluorescence statistical distributions for healthy and unhealthy donors. The statistical signs of transcritical bifurcation provide the classification of all available immunofluorescence histograms into three large groups. The first group corresponds to oncology and autoimmune diseases; the second group corresponds to inflammatory diseases; the third group corresponds to healthy donors. The fluorescence histograms for pregnant women on the other hand show two groups of health status. The immunofluorescence analysis supplements a well-known biochemical analyses. Some discussions on biophysical and biomedical analogies for the proposed approaches with another physical classifications, such as bronchial tree, pathology of heart rhythms, different bistabilities switching and others, are presented.