["Freezing" of the conformation of thin filaments in a single skinned fiber of the rabbit muscle by glutaraldehyde]. / "Zamorazhivanie" konformatsii tonkikh nitei v odinochnykh demembranirovannykh voloknankh myshtsy krolika gliutarovym al'degidom.

It is shown that short treatment of a single skinned rigor fibre from rabbit m X psoas with 0.05% glutaraldehyde in the absence of Ca ions leads to a modified state of the contractile apparatus. After the addition of 5 mM MgATP in the absence of Ca ions to the fibre a sharp rise and subsequent slow decay of tension were observed in contrast to the tension drop in case of the control (unmodified) specimen. The tension transients following quick stretch (L 0.5%) were similar to those for Ca-activated tension. In case of the modified relaxed fibre such a phenomenon was not observed. These results can be explained by "freezing" with glutaraldehyde the thin filament structure either in the "on" or "off" states. The relation of these results to the cooperativity in the regulation mechanism of contraction is discussed.

[X-ray diffraction study of the molecular nature of the dependence of rigor tension developed by skinned rabbit psoas muscle on the ionic strength of the solution]. / Rentgenograficheskoe izuchenie molekuliarnoi prirody zavisimosti rigornogo napriazheniia, razvivaemogo demembranizirovannymi puchkami volokon spinnoi myshtsy krolika, ot ionnoi sily rastvora.

Molecular origin of the dependence of rigor tension developed by skinned rabbit psoas muscle on the value of ionic strength in rigorizing solution was studied by means of X-ray diffraction technique. It is shown that a deviation of the ionic strength from "normal" value (= 0.125) either to high (= 0.34) or to low (= 0.04) values is accompanied by the changes in the relative intensities of some meridional reflections while their axial positions remained unchanged. This may be explained as the result of the detachment of myosin subfragments-2 from the surfaces of thick filaments. The data obtained indicate that there is a correlation between the structure and localization of myosin subfragments-2 and the value of force generated by the muscle.

[X-ray diffraction study of the rabbit psoas muscle with extracted H-zone]. / Rentgenograficheskoe issledovanie spinnoi myshtsy krolika s ékstragirovannoi H-zonoi.

Fibre bundles of glycerinated rabbit psoas muscle about 0.5-1.0 mm thick were incubated in 5 mM tris-(hydroxymethyl)-aminomethane (Tris), pH 8.0 for 5-20 hours at 4 degrees C. This treatment leads to selective removal of some proteins in the M-bands and H-zones of sarcomeres. Effects of extraction were analyzed on the basis of electron micrographs of longitudinal sections of muscle specimens, gel electrophoresis patterns of myofibrils and of the extracts, and measurements of the creatine kinase activity of myofibrils. In the X-ray diffraction patterns of the fibre bundles subjected to prolonged extraction a drastic decrease in the intensity of "442 A" and "223 A" meridional reflections and a considerably smaller decrease in the intensity of "212 A" meridional reflections were observed. The "147 A" meridional reflection remains practically unchanged. It was concluded that: (1) The reflections "442 A" and "223 A" were contributed mainly by diffraction on the minor proteins located in the central part of the thick filaments in between the C-zones. This is contrary to the widely accepted viewpoint according to which the appearance of "442 A" reflection is caused only by the C-protein component of the thick filaments. (2) The "147 A" meridional reflection is contributed mainly by C-protein and light meromyosin of the thick filaments.

[Dependence of rigor tension developed by skinned rabbit psoas fibers on the ionic strength of solution]. / Zavisimost' rigornogo napriazheniia, razvivaemogo demembranizirovannymi voloknami spinnoi myshtsy krolika, ot ionnoi sily rastvora.

The magnitude of isometric tension developed by a bundle of skinned rabbit psoas fibers when it is transferred from relaxing to rigor solution strongly depends on the ionic strength value of the bathing rigor solution. Upon elevation of the ionic strength from 0.04 to 0.34 the rigor tension declines about 2.3 times.

[X-ray study of the effect of pyrophosphate on thick filament structure in skinned fiber bundles of the rabbit psoas muscle]. / Rentgenograficheskoe issledovanie vliianiia pirofosfata na strukturu tolstykh nitei v demembranizirovannykh puchkakh volokon spinnoi myshtsy krolika.

Structure of thick filaments in the chemically skinned fibre bundles of rabbit psoas muscle in a state of pseudorelaxation induced by adding 2 mM pyrophosphate (PP) and of PP-mixture with 40% ethyleneglycol to the bathing rigor solution was studied with the help of X-ray diffraction technique. Reduction in the isometric rigor tension by about 50-70% in a state of pseudorelaxation is accompanied by significant changes in the relative intensities of a number of meridional reflections, indicating that in situ the structure and location of S-2 segment may be regulated by the structural changes in the acto S-1-complex during its cyclic interaction with ATP.

[X-ray study of pH-dependence of thick filament structure in stripped fiber bundles of vertebrate skeletal muscles]. / Rentgenograficheskoe izuchenie zavisimosti ot pH struktury tolstykh nitei v demembranizirovannykh puchkakh volokon skeletnykh myshts pozvonochnykh.

Molecular origin of pH-dependence of rigor tension in chemically skinned fibre bundles of rabbit psoas muscle was studied with the help of X-ray diffraction technique. It was found that a shift of pH from the neutral value of about 7.0 either to basic or to acidic regions by one unit is accompanied by changes of relative intensities in a number of meridional reflections. These effects are explained as the result of pH-induced detachment of subfragments-2 of myosin molecules from the thick filament surface. The data obtained indicate that force generation in muscle may be caused by the structural changes of subfragments-2 of myosin molecules.

[Interpretation of the pictures of meridional diffraction on X-rays of membrane-free rabbit spinal muscles in a state of rigor and their dependence on physico-chemical parameters of rigorising solution]. / Interpretatsiia kartin meridional'noi difraktsii na rentgenogrammakh demembranizirovannoi spinnoi myshtsy krolika v sostoianii rigora i ikh zavisimosti ot fiziko-khimicheskikh parametrov rigorizuiushchego rastvora.

Results of the studies of structural and mechanical properties of rabbit psoas muscle by means of X-ray diffraction and physiological technique are summarised along the following lines: localisation of minor proteins in the thick filaments and the origin of meridional reflections in the X-ray diffraction patterns of rigorised rabbit psoas muscle; molecular basis of the effects of pH, ionic strength, pyrophosphate, ethyleneglycol and pyrophosphate-ethyleneglycol mixture on the value of rigor tension and their dependence on the sarcomerès length and concentration of Mg2+; effect of selective extraction of minor proteins from M- and P-zones of the thick filaments on meridional reflections; structure of the thick filaments in the state of "Ca2+-free rigor"; attachment of cross-bridges to actin filaments in relaxing solution (is the model of "sterick brocking" correct?); role of structural transitions in S-2-segments of myosin in force generation.

[Direct proof of the existence of Ca2+-induced structural changes in miosin-containing thick filaments of vertebrate skeletal muscles]. / Dokazatel'stvo sushchestvovaniia Ca2+-indutsiruemogo strukturnogo perekhoda v stvolakh miozinsoderzhashchikh nitei skeletnykh myshts pozvonochnykh.

Frog sartorius muscles were skinned with the help of detergent Triton X-100 in relaxing solution and then rigorized in the solution free of ATP and calcium (Ca2+-free rigor). Some of the X-ray diffraction patterns obtained from such muscles differed drastically from the patterns of usual "calcium" rigor state of the muscle. Analysis of the X-ray diffraction patterns of Ca2+-free rigor state of the muscle allows the following conclusions to be made. (1) It is proved that the so-called forbidden meridional reflections localised in groups at the successive orders of the repeat period of about 430 A are due to diffraction on the lattice formed by minor proteins of the thick filaments. This must be taken into account while interpreting the intensity changes of the meridional 143 and 215 A reflections in the contracting muscle. (2) The shafts of the myosin-containing filaments may exist in two different structural states; the transition between these states takes place on the change of calcium concentration. (3) The deflection of myosin cross-bridges from the shafts of the filaments is possible at either of two conformations of the myosin shafts. (4) The formation of actomyosin rigor-complexes does not necessarily leads to a structural change in the myosin filament. (5) Existence of Ca2+-induced structural changes in the thick filaments indicates possible myosin-linked regulations in the vertebrate skeletal muscle alongside with the actin-linked ones.

[Location of adenine nucleotides in striated fibers of skeletal muscles]. / O lokalizatsii adeninnukleotidov v poperechnopolosatykh voloknakh skeletnykh myshts.

The absorption of light at 265 nm wave length in isolated muscle fibers and myofibrilles of vertebrate striated muscle was investigated with the aid of microscope with the wide spectral range (240--900 nm), equipped with image intensifier and recording cine camera. It was established that freshly isolated nonfatigue frog fibers absorbed UV-light along the entire of the length of the fiber. This fact attests the uniform distribution of ATP and some other nucleotides in the myoplasma of muscle cell. The fatigue of the fibers results in the appearance of a cross--striated pattern along the length of fiber, determinated by the alternation of the sarcomere regions with different degree of light absorption at the given wave length. The regions of the most heavily absorption of UV corresponds to the I-, M-, and N-bands of sarcomere. The comparison of the data obtained from intact and glycerinated fibers and also from myofibrilles with extracted A-bands allows to suppose that the absorption bands at 265 nm wave length are the places of location of bound ADP, RNA and minor fraction of ATP.

[Localization of minor proteins and structural changes in the myosin filaments of vertebrate striated muscle]. / Lokalizatsiia minornykh belkov i strukturnye izmeneniia v miozinovykh poperechno-polosatykh myshts pozvonochnykh.

The origin of meridional reflections in the X-ray diffraction patterns of vertebrate skeletal muscles in resting and rigor states was studied. The main results may be summarized as follows. 1. Most of the meridional reflections localized in groups at the positions of successive orders of the repeat period of about 430 A are contributed mainly by the C-protein component of thick filaments. 2. The meridional reflections at about 143 and 72 A in the X-ray diffraction pattern of the resting muscle are contributed mainly by the cross-bridge axial repeat period, while in the X-ray diffraction patterns of the rigorized muscle the reflections at approximately the same positions are contributed mainly by C-protein. The change in the positions of these particular reflections accompanying the transition of the muscle from rest to rigor and from rest to contraction cannot be considered as an indication of a change in the axial repeat period of the cross-bridges, as it was earlier suggested by some authors. 3. The transition of the muscle from resting to rigor state is accompanied by substantial changes in the positions of the meridional reflections contributed my minor proteins, which is indicative of the structural transition in the thick filaments. The observed changes may be interpreted as the result of the thick filaments elongation by about 1.5% or, alternatively, as a consequence of the redistribution of electron density of the meridional reflections 215 and 143 A during a single twitch of the muscle (Huxley et al., Nature, 1980 284, 140) may be interpreted as a natural consequence of the structural change in the thick filaments. It is concluded therefore that on stimulation of the vertebrate skeletal muscle the thickness filaments undergo a reversible structural change which may reflect the existence of myosin-linked regulation in that type of muscle.