[Correlation between Ca2+-dependent movement of crosslinks in myosin filaments and Ca2+-sensitive actin-activated ATPase of skeletal muscle myosin]. / Korreliatsiia mezhdu Ca2+-zavisimym dvizheniem mostikov v miozinovykh nitiakh i Ca2+-chuvstvitel'nost'iu aktin-aktiviruemoi ATFazy miozina skeletnykh myshts.

The dependence of actin-activated ATPase activity and myosin filament structure have been studied on Ca(2+)-concentration in the range between pCa 7.5 and pCa 4.6. Rabbit skeletal muscle myosin with dephosphorylated regulatory light chains column-purified with DEAE-Sephadex A-50 for the removal of minor proteins and actin without regulatory proteins have been used. Considerable increase in actomyosin ATPase activity (by 70%) is revealed with increasing Ca(2+)-level from pCa 7.5 up to pCa 4.6. Electron microscopic observations on the structures of reconstituted myosin filaments have revealed Ca(2+)-dependent movement of myosin cross-bridges (head + subfragment-2) from and to the backbone of myosin filaments. The correlation between the manifestation of Ca(2+)-sensitivity of ATPase properties of myosins and Ca(2+)-dependent mobility of cross-bridges has been established. In particular, the increase in the mobility of cross-bridges and their moving away from the surface of myosin filaments at pCa 4.6 correlates with the increase in actin-activated ATPase of the same myosin preparations. It is supposed that the interrelation between the above properties observed in in vitro system can be of importance for force generation and its regulation in muscle.

[Effect of phosphorylation of light chain myosin and Ca2+ on the conformation of F-actin during skeletal muscle contraction]. / Vliianie fosforilirovaniia legkikh tsepei miozina i Ca2+ na konformatsiiu F-aktina pri sokrashchenii skeletnykh myshts.

The dependence of polarized fluorescence of rhodaminylphalloin specifically bound to F-actin and the tension developed by a fiber upon phosphorylation of myosin (18.5 kD) light chains as well as on the concentration of free Ca2+ was observed during the contraction of glycerinated rabbit skeletal muscle fibers. Still greater changes in the polarized fluorescence and higher values of tension were recorded for fibers with phosphorylated light chains at low (0.6 microM) Ca2+ concentrations as well as for those with dephosphorylated light chains at high (10 microM) Ca2+ concentrations. It is concluded that phosphorylation of myosin light chains modulates skeletal muscle contraction. The mechanisms of modulation involve conformational changes in F-actin.

[Production of glycerinated models of muscle fibers with phosphorylated myosin light chains]. / Poluchenie glitserinizirovannykh modelei myshechnykh volokon s fosforilirovannymi legkimi tsepiami miozina.

A simple method for obtaining glycerinated muscle fibres of m. psoas of rabbit containing regulatory myosin light chains (LC2) of different levels of phosphorylation. The glycerination conditions stimulated endogenic kinase LC2 or phosphatase LC2. Glycerinated muscle fibres contained phosphorylated and dephosphorylated (levels of phosphorylation are 95 +/- 5%, and 5 +/- 5%, respectively) LC2 of myosin. To determine the level of phosphorylation the method of polyacrylamide gel electrophoresis in 8 M urea was modified.

[Phosphorylation of light chains of myosin from rabbit skeletal muscles affects the type of conformation changes of F-actin induced by heavy meromyosin]. / Fosforilirovanie legkikh tsepei miozina iz skeletnykh myshts krolika vliiaet na kharakter konformatsionnykh izmenenii F-aktina, indutsiruemykh tiazhelym meromiozinom.

The changes in F-actin conformation in myosin-free single ghost fiber induced by the binding of heavy meromyosin (HMM) with dephosphorylated or phosphorylated light chains-2 (LC2) have been studied by measuring intrinsic tryptophan polarized fluorescence of F-actin. It has been found that at low concentrations of Ca2+ (pCa greater than or equal to 8), the binding of HMM with dephosphorylated LC2 to F-actin in ghost fibres increases, whereas the binding of HMM with phosphorylated LC2 decreases the anisotropy of polarized tryptophan fluorescence. The effect is reversed at high concentrations of Ca2+ (pCa = 5). It has been assumed that this effect of myosin light chains phosphorylation may be due to its influence on the type of myosin head binding to F-actin.