[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.

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.

[Superprecipitation of synthetic actomyosin after denervation]. / Superpretsipitatsiia sinteticheskogo aktomiozina posle denervatsii.

Superprecipitation of synthetic actomyosin formed from intact myosin and actin extracted from rabbit white skeletal muscles after denervation was compared with that of intact synthetic actomyosin. Superprecipitation was characterized by two parameters: (1) the value of superprecipitation delta E determining an increase in the absorption from minimum to maximum values, and (2) the time required for the half-maximum increase (t1/2) which is inverse of the velocity constant. It was shown that delta E and the velocity constant decrease and t1/2 after denervation. It is assumed that this effect is related to the changes in actin structure.

[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.

Effect of denervation on the properties of actin (according to superprecipitation data).

The superprecipitation of synthetic actomyosin, formed from intact myosin and actin extracted from rabbit white skeletal muscles 14 and 75 days after denervation has been compared with that of intact synthetic actomyosin. Superprecipitation has been characterized by two parameters. 1. The value of superprecipitation delta E determining the increase in the absorbance from minimum to maximum values; 2. the time required for the half-maximum increase (t 1/2) which is the inverse of the velocity constant. It has been shown that both the delta E and the velocity constant decrease: the delta E amounts to 75.4 +/- 7.3 per cent (p = 0.95) and 87.9 +/- 11.2 per cent (p = 0.95) after 14 and 75 days, respectively, when compared with normal; the t 1/2 increases to 41.5 +/- 13.6 per cent (p = 0.95) after 14 days and 17.5 +/- 11.9 per cent (p = 0.95) after 75 days. It is assumed that this effect is related to changes in the structure of actin.

[Estimation of the amount of energy transformed in the actomyosin--ATP system according to kinetics findings]. / Otsenka velichiny énergii, preobrazuenoi v sisteme aktomiozin--ATF, op dannym kinetiki

A kinetic scheme for actomyosin ATPase reaction, including two different states of the energy-rich actomyosin intermediate and different ways of its formation and decomposition, is considered. The energy, liberated in this reaction, amounts to 9 kcal. mol-1. Energy liberation is coupled with myosin head rotation. The energy-rich intermediate is stabilized by hindrances to head motion. By this mechanism the energy transduction in a filamentous actomyosin system can occur only after a dissociation act, and an ordered cyclical reaction can take place.

[Are the reciprocal sliding of protofibrils and the shortening of thick filaments during muscle contraction based on a common molecular mechanism?]. / Mogut li vzaimnoe skol'zhenie protofibrill i ukorochenie tolstykh nitei pri myshechnom sokrashchenii osnovyvat'sia na obshchem molekuliarnom mekhanizme?

It is assumed that the back stroke of myosin bridges in a contracting fibre is determined by nucleotide binding. Then an inhibition of actomyosin dissociation can lead to the shortening of the thick filaments. Possible existence of a protein control system, suppressing this dissociation is discussed.

[Energy conversion of the phosphate bond in the actomyosin-ATP system, accompanied by acceleration of myosin adenosine triphospatase]. / Preobrazovanie énergii fosfatnoi sviazi v sisteme aktomiozin--ATF, soprovozhdaemoe uskoreniem adenozintrifosfatazy miozina.

A possible mechanism of the active motion ("tilt") of the actin-bound myosin head in ATP hydrolysis reaction is considered. This motion is considered. This motion can be goverened by actinmyosin affinity changes at two sites located on the head. Such an affinity change is assumed to take place already in the macroergic myosin (M) -products (P) complex MP. Then at a contact with actin a tilting force is generated, and the M energy liberation, coupled with the head ratation, goes on with a concomitant potential barrier lowering and corresponding acceleration of the MP destruction. In this way a destruction. In this way a decrease of free energy with a change of the head orientation is equivalent to the energy liberated, which amounts to 9 kcal.mol-1.

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.