[Optical trap as a tool for studying motor proteins].

The review is concerned with the optical trap method, a modern experimental tool based on the recently discovered ability of light to trap and hold micron and submicron particles in the focused beam. The physical principle of operation of the optical trap and the possibilities of using the tool in studies of the molecular nature of biological motility have been considered. Some studies devoted to the physical characteristics and functioning of single molecules of motor proteins have been analyzed that have been performed with the optical trap method, which allows one to record nanometer displacements and piconewton forces.

[The in vitro motility assay to study the calcium-mechanical relationship in skeletal and cardiac muscles].

In a series of experiments on regulated contractile systems (i.e., in vitro mobile systems with reconstructed thin filaments), the velocities of the movement of a thin filament on the surface covered by either rabbit skeletal or rat cardiac myosin at various concentrations of calcium ions in solution (in the pCa range from 4 to 8) were assessed. The corresponding "pCa-velocity" relationships were plotted, which proved to be of the sigmoid form. It was found that, at a saturating calcium concentration (pCa 4), the velocity of regulated thin filaments was 65% higher than for unregulated ones in the case of skeletal myosin and 87% higher than for unregulated thin filaments in the case of cardiac myosin. It was also found that the Hill coefficient was 1.95 and 2.5 for skeletal and cardiac myosins, respectively. The difference in the Hill coefficients for skeletal and cardiac myosins is discussed in terms of the difference in contribution of cooperativity mechanisms of contractile and regulatory proteins in the regulation of contraction in these types of muscles.