Contractile properties of chick embryo muscles in development.

In this paper we report on the observation of two parameters of embryonic muscles which show the functional activity of myofibrillar ATPase activity of embryonic muscles and superprecipitation (SP) of natural actomyosin. Our results indicate that, during the embryonic period, the myofibrillar ATPase activity and the SP of actomyosin significantly increased, the rate of this increase being different for leg and breast muscles.

[ATPase activity and the contractile capacity of the muscle tissue in chick embryos during development]. / ATFaznaia aktivnost' i "sokratitel'naia sposobnost'" myshechnoi tkani kurinykh émbrionov v protsesse razvitiia.

The value of ATPase activity of the myofibril preparations and the value and duration of actomyosin superprecipitation were estimated for different muscles during the chick embryonic development. The ATPase level increases during embryogenesis 4.5-fold, in the leg muscle this change takes place distinctly earlier than in the leg muscle. The value and rate of actomyosin superprecipitation also markedly increase, to a lesser extent for m. soleus than for m. pectoralis. It is suggested that these changes and differences are mainly due to the delay in synthesis of certain types of the embryonic myosin light chains.

[Myosin isoforms of skeletal muscles in development]. / Izoformy miozina skeletnykh myshts v razvitii.

The latest data are reviewed concerning identification of myosin from the skeletal muscle during embryonic and postnatal development in vertebrates. The data are given on the composition of light subunits and specificity of heavy chains of the early isoforms obtained by electrophoresis, peptide mapping, DNA-RNA hybridization, as well as immunological methods with poly-and monoclonals. The substitution of embryonic heavy chains by neonatal and definitive ones is discussed. The following items are also considered: early isoforms of the fast and slow myosin types and, in particular, endogenous program directing the muscle development and protein synthesis towards the "fast phenotype", which is modulated by neurostimulation and other physiological factors inducing slow myosin type. The enzymatic activity of the early isoforms and its physiological importance in embryogenesis are discussed.

Contraction induced by antibodies to paramyosin in glycerinated fibers of Barnacle giant muscle in an ATP-deficient medium: a possible function of paramyosin.

Glycerinated giant muscle fibers of the barnacle Balanus rostratus in an ATP-deficient solution respond to antibodies to paramyosin (aPM) by an isometric tension development followed by an immediate spontaneous relaxation. The aPM presence does not affect the subsequent contraction and relaxation of the fibers in suitable ATP-containing media. The effects of ATP and aPM present together in a contracting medium are additive. The aPM effect is caused assumedly by a sudden shortening of some highly elastic connecting filaments which are linked in a stretched and strained state to the thick filament by its paramyosin, aPM dissociates this link. Possible specific functions of paramyosin in various types of muscles are discussed.

[The paramyosin function in glycerinated muscle fibers during blocking with antibodies of its contacts with structural proteins]. / Izuchenie funktsii paramiozina v glitserinizirovannykh voloknankh myshts pri blokirovanii antitelami ego kontaktov so strukturnymi belkami.

Antibodies to paramyosin (APM) induce a partial decrease of the isometric tension in glycerinated fibres of the Anodonta cygnea catch muscle in the presence of ATP and Ca2+; the myofibrillar Mg2+ ATPase increases concomitantly. Assumedly paramyosin inhibits the cross-bridges unlocking, retaining them mechanically in a locked state. The fibres of barnacle giant muscle in an ATP deficient solution respond to APM by transient isometric tension development. A model for the participation of paramyosin in the contractile process is proposed. In both muscle types paramyosin hinders the functioning of certain elements of the contractile machinery.

Actomyosin adenosine triphosphatase regulation by intramolecular myosin mechanisms. Myosin light chains functions and rod modification effects.

Mechanisms of the actomyosin ATPase modulation via the myosin light chains (LC) in various myosin types are discussed. The essential LC increase the stability of the myosin heavy chains (HC) in the myosin heads and, under certain conditions, they can affect the degree of interaction of HC with actin. The regulatory LC (RLC) are sensitive to calcium binding on specific sites or to calcium activated phosphorylation. These factors induce changes of the RLC state followed by changes of the HC state in response to calcium concentration changes during the contractile process. Direct calcium binding or phosphorylation effects in various muscles are mediated by special types of RLC and HC. Several examples of actomyosin ATPase changes induced by modifications of the myosin rod are compared. A common feature of these effects is a possible involvement of certain configurational changes of the myosin molecule. These changes can affect the spatial position of the myosin heads and the myosin-actin interaction.

Effect of antibodies to light meromyosin on glycerinated muscle fibres and on actomyosin adenosinetriphosphatases.

The conformation change of light meromyosin influences the myosin and actin interaction, the myosin ATPase activity [22]. Starting from these data the specificity of the phenomenon has been investigated. The effect of LMM1, LMM- and LMM1-antibodies was studied on the isometric tension and relaxation of glycerol extracted muscle fibres. LMM1 was found to relax the fibres isometrically contracted by ATP-Ca2+; anti-LMM and anti-LMM1 markedly accelerated the development of isometric tension and inhibited the relaxation of ATP contracted glycerinated muscle fibres; in the presence of anti-LMM the ATPase rate of glycerinated myofibrils was slightly augmented. These results seem to indicate that LMM1 governs the actin binding site function of myosin and controls its affinity to actin. It is supposed that the reaction of myofibrils with specific LMM antibodies induced a transconformation in the myosin head increasing the affinity to actin of myosin.

[Secondary structure and amino acid composition of protein complex associated with the rod part of myosin molecule]. / Vtorichnaia struktura i aminokislotnyi sostav belkovogo kompleksa, sviazannogo so sterzhnevoi chast'iu molekuly miozina.

The secondary structure and amino acid composition of a protein complex (LMM-Rp) bound to the heavy chains (HC) of light meromyosin (LMM), and the secondary structures of LMM and its fractions obtained at an intermediate stage of LMM-Rp preparation were studied. The data obtained were compared with the similar ones for LMM HC and for the myosin light chains (LC). For the secondary structure study the data of CD-spectra were used. This structure was characterized by molar parts of the amino acid residues belonging to four different conformations: alpha-helices, beta-structures, beta-bends and irregular coils. In LMM-Rp unlike HC and LC, the alpha-helices are nearly absent, and appreciable parts of irregular coils and beta-bends are present. The amino acid compositions of LMM-Rp, HC and LC markedly differ. This difference is more significant when LMM-Rp is compared with HC, then with LC. This is an accordance with comparable data for the secondary structure.

Distribution of cholinesterases of rabbit skeletal muscle.

Two cholinesterase (ChE) fractions were extracted from homogenates of rabbit skeletal muscle. One of them the sarcoplasmic ChE could be dissolved quantitatively with solution A. Following the extraction with solution B the myofibrillar ChE fraction could be recovered. The ChE-activity of the sarcoplasmic extract was about 38% and the activity of myofibrillar extract was about 50% of the ChE-activity of muscle homogenates. According to our calculations about 10-12% of the total ChE-activity is insoluble. By the aid of PAGE seven zones of ChE-activity could be distinguished in the sarcoplasmic extract. The activity of myofibrillar ChE-fraction was obtained by chromatographic purification of LMM. The LMM1 proved to be inhomogeneous with PAGE, however, only one fraction displayed ChE-activity. Immune-serum produced against myosin did not give reaction with purified sarcoplasmic ChE, only with the myofibrillar fraction. Our results suggest that the heterogeneous distribution of muscle ChE-es in different molecular forms is not an artifact.

[Complex biochemical and structural study of skeletal muscles in scoliosis]. / Kompleksnoe biokhimicheskoe i struktornoe issledovanie skeletnykh myshts pri skolioze.

Structural study of human scoliosis muscles showed significant dystrophic and degenerative changes: desintegration of fibrillar structure and striation; the Zencker necrosis; the replacement of muscular tissue by connective and adipose tissues. The electron microscopic observation revealed disordering of filamental array of the sarcomere (I- and A-discs), the broadening of Z-disc material, the appearance of N-stripes in I-band. At the same time deviations from the norm were observed in contractile proteins: actin and myosin. ATPase activity of myosin decreased by 25--30%; the flow of birefringence of myosin and especially of actin also decreased. Actin from the scoliosis muscles partially or completely lost the ability for polymerization in 0.1 M KC1.

[Structural and functional changes in myosin in chronic coronary insufficiency]. / Strukturnye i funktsional'nye izmeneniia miozina pri khronicheskoi nedostatochnosti serdtsa

A study of myosin extracted from dog's cardiac muscle at different stages of chronic heart failure (from 1 week to 1 year) was carried out. A decrease of UV-luminescence intensity, flow birefringence and ATPase activity (to 70%) was observed. The electron microscopic investigation of myosin and LMM structure shows the loss of ability to form typical paracrystals by LMM, the electron microscopic appearance of the whole myosin being unchanged.

The effect of denervation upon the functional properties of myosin and its fragments.

A study has been made of some structural and enzymatic properties of myosin and its fragments from denervated white muscles of rabbit in the course of atrophy using different methods: UV-luminiscence, flow birefringence, electromicroscopy, viscosimetry and enzymatic measurements. All the studied parameters had a tendency to decrease; at prolonged observation some properties were partially restored. Considerable changes of structural properties of LMM were revealed: the ability of LMM from denervated muscle to form high-ordered structures which is characteristic of LMM from normal muscle decreased considerably.

The inhibitory action of the light meromyosin component on the myofibrillar and actomyosin atp-ase.

The protein component of light meromyosin [LMM-1] was shown earlier to relax glycerinated muscle fibres and actomyosin. Presently its influence on ATP-ase activity of myofibrils, actomyosin, myosin and heavy meromyosin has been studied. LMM-1 decreases Mg-ATP-ase activity of myofibrils and of reconstructed actomyosin by 25-- 30% and does not change [or slightly increases] Ca-ATP-ase activity of this protein and of myosin; besides LMM-1 is able to increase Mg-ATP-ase of HMM substantially. LMM-1 markedly inhibits [preliminary data] the activation of ATP-ase activity of HMM by actin. It is suggested that LMM-1 protein interacts with myosin and decreases the actin-myosin affinity, displacing actin out of the complex. It reacts only with one of the heads of myosin. Probably this suggestion can account for a relatively slight inhibition of ATP-ase activity of complex by LMM-1. LMM-1 represents a natural and specific inhibitor of Mg-AM-ATP-ase activity, included in the structure of myosin protofibrils and interacting with the myosin active site region.