[Thin filament elasticity and its role in the muscle contraction].

The available experimental methods do not allow one to establish unambiguously the molecular structural events during muscle contraction. To resolve the existing controversies, I have devised an unconventional original computer program. The new approach allows the reconstruction of the hexagonal lattice of the sarcomere for different muscle states and verification of the structure by comparison of the calculated Fourier spectra with the real diffraction patterns. Previously, by the use of this approach, the real structure of a myosin filament from vertebrate striated muscle has been reconstructed (http://zope.ibib.waw.pl/pspk). In this work, a reconstruction for the thin filament is presented for three states: relaxed, after activation, and during contraction. Good consistency of the calculated Fourier spectra with the real diffraction patterns available in the literature suggests that the thin filament, due to flexibility, plays an active part in muscle contraction, as myosin cross-bridges do.

Computer system modelling muscle work.

In the work, an original computer system, called Muscle, is described. The Muscle allowed modelling of the whole thick filament with different arrangements of the myosin tails and myosin heads. Computer simulation and animation have revealed that only the model of the thick filament with asymmetrical configuration of the crossbridges has 3-fold rotational symmetry and assures matching between many thousands specific binding-sites on myosin heads and actin monomers. The Muscle delivered a number of arguments that the hypothesis of near parallel packing of the myosin tails, as well as oar-like or lever-arm-like work of the myosin crossbridges, is unfounded. We have presented advantages of the computer simulation in studies of complicated 3D molecular objects especially when direct observation is technically impossible.

[Structure and functional significance of the thick filament]. / Struktura i funktsional'noe znachenie tolstoi niti.

New models of the thick filament structure and muscle contraction are proposed in the work. Association of myosin molecules into filament occurs by intertwisting between them. The model is in good consistency with experimental data. A computer analysis of the widely accepted concept of parallel packing of myosin molecules is presented. It is shown that the rowing movement of crossbridges resulting from parallel packing is, on the one hand, impossible in terms of sarcomere construction, and on the other hand, is in conflict with available experimental data. The crossbridge movement by unwrapping easily agrees with recent experimental data as well as given possibility to interpret such phenomena as the change of the myofilament dimensions under certain conditions or step-wise manner of sarcomere contraction.

Mechanism of muscle contraction.

This work is the first attempt to propose a complex model of muscle contraction in which different aspects of the sarcomere shortening are collected into a logical entity. Proposed are some suggestions to answer some fundamental questions concerning the molecular mechanism of muscle contraction, such as the following: "of which part of the myosin molecule does the crossbridge consist?", "how does the crossbridge act?", "what are two heads of the myosin molecule needed for?", "in what way is the metabolic energy of ATP converted into the mechanical work of muscle contraction?", "does the actin filament influence have a passive or active role in the process of muscle contraction?", "what is the role of the third filament - a connecting one?", "in what way is muscle relaxation generated?".