[Contractile proteins in the fractions of soluble and insoluble chromatin of liver and thymus]. / Sokratitel'nye belki v sostave rastvorimogo i ostatochnogo khromatinA pecheni i timusa.

The proteins corresponding in molecular weight and solubility in salt solutions to skeletal muscle actin and myosin were revealed in liver and thymus chromatin fragments. When the ionic strength reached 0.3, about 60% of the myosin-like protein identified by electrophoretic mobility of high chains and the K+-EDTA-ATPase activity was cosedimented with nucleohistones. In the presence of ATP or PPi and Mg2+ the solubility of myosin in such salt solutions increased up to 90%, which was paralleled with significant stimulation of RNA release from the nucleohistones. The conformity in the degree of extraction and sedimentation of RNA and intranuclear myosin was also observed in other solutions used during myosin purification. The supposition that the nuclear system of contractile proteins causes labile, ATP-dependent binding of RNA to chromatin is discussed. No essential differences in the actin or myosin contents in the fractions of soluble and non-soluble chromatin were detected.

[Localization of the ATPase site of nitrogenase by isotopic oxygen exchange [180]-Pi in equilibrium with H20]. / Issledovanie lokalizatsii ATPaznogo tsentra nitrogenazy metodom izotopnogo obmena kisloroda [180]-Pi v ravnovesii H20.

The components of the nitrogenase complex, MoFe-protein and FeMo-cofactor, possessing no ATPase or nitrogen-fixing activity, maintain the 18O-exchange at the level of 1 atom of 18O per molecule of Pi, which is inhibited by ATP. The Fe-protein complex does not catalyze the 18O-exchange. The nitrogenase components do not hydrolyze the substrates for phosphatase (p-nitrophenylphosphate, beta-glycerophosphate, glucose 1-phosphate and ribose 5-phosphate). The artificial albumin-containing MoFe- and Fe-proteins and the carboxyl group-containing proteins (albumin, hemoglobin, lysozyme) as well as sodium molibdate do not catalyze the 18O-exchange. It is assumed that the site of the ATPase center which is subjected to phosphorylation, is located on the MoFe-protein.

A study of the 18O-exchange reactions catalyzed by cardiac myosin and its subfragment 1.

Isotope-exchange reactions (H2(18)O in equilibrium with KH2PO4) during ATP hydrolysis catalyzed by myosin and its subfragment 1 from rabbit, dog, and human cardiac muscle were studied. All preparations of myosin and subfragment 1 in the presence of Mg2+ catalyzed two types of 18O-exchange reactions similar to those of skeletal muscle: intermediate and direct 18O exchange. The dependences of both reactions on divalent metals and nucleotides were studied. Data on 18O exchange of subfragment 1 from rabbit, dog, and human cardiac muscle were obtained for the first time. They indicate the similarity of molecular mechanisms of ATP energy use in cardiac and skeletal muscle contraction.

[Role of adenosine triphosphatase on nitrogenase function]. / O roli adenozintrifosfatazy v funktsionirovanii nitrogenazy.

The decoupling possibility of ATPase reaction with electron transfer process in the time of nitrogenase photolysis by lambda 435 nm light has been established. The COOH and the possibility of imidazole groups have been revealed in nitrogenase ATPase centre by methods of chemical modification. The reaction of direct 18O-exchange between inorganic phosphate and medium water was discovered, proceeding under reverse hydrolysis of acylphosphate bond, formed by phosphorylation of COOH-group in ATPase centre. Direct 18O-exchange was shown to be stimulated by ATP and ADP, but to be insensitive to GTP, CTP, AMP-nucleotide which are not ATPase centre substrates. The coupling mechanism of ATPase reaction with electron transfer is suggested; it is based on the possibility of compulsory protonation of Fe-S-cluster at the expense of proton transfer from the imidazole site, facilitating additional electron transfer under "superreduction" of nitrogenase component of the Mo-Fe-protein. It is assumed that this protonation is initiated by COOH-group of charge relay transfer with imidasole fragment.

[Modern views on mechanism of ATP hydrolysis by myosin (on the 40th anniversary of myosin enzymatic activity discovery)]. / Sovremennye predstavleniia o mekhanizme gidroliza ATP miozinom (k 40-letiiu otkrytiia fermentativnykh svoistv miozina).

Literature data and the author's materials concerning the intermediate stages of ATP hydrolysis by myosin and actomyosin are reviewed. The scheme of hydrolytic stages based on the application of fluorescent and UV spectroscopic stop-flow and 18O exchange methods is discussed. Some unsolved problems of the hydrolytic mechanism and its relation to energy transduction in the mechanochemical act are also considered.

[18 O-exchange during ATP and n-nitrophenylphosphate hydrolysis by Na, K-ATPase from bovine brain]. / 18- 180-obmen v khode gidroliza ATP i n-nitrofenilfosfata Na, K-ATPazoi iz mozga byka.

The reaction of the oxygen isotope exchange (18O-exchange) was studied in the course of the Na, K-ATPase reaction. It was shown that the intermediary and direct 18O-exchanges occurred in the system in the presence of both ATP and p-NPP. These findings are indicative of the same intermediate during the hydrolytic process in both cases. The intermediary 18O-exchange was activated by N-ethylmaleimide, hydroxylamine and 2.0--1.5 18O atoms, respectively. The detection of 18O-exchange Ouabain had no effect on the exchange. The levels of intermediary 18O-exchange during ATP and p-NPP hydrolyses were equal to 1.3--1.4 and 2.0--1.5 18O atoms, respectively. The detection of 18O-exchange reactions at the intermediary steps of both ATP and p-NPP hydrolyses implies the identity of certain stages in the destruction of these substrates by Na, K-ATPase.

[18 O-exchange reactions catalyzed by myosin of calf intestine smooth muscle]. / O 18-obmennye reaktsii, kataliziruemye miozinom gladkikh myshts kishechnika telenka.

18O-exchange reactions of smooth muscle myosin of calf intestine were studied. Smooth muscle myosin, similar to skeletal myosin, catalyses two types of 18O-exchange reactions--intermediate and direct. Only quantitative differences of the exchange intensity are observed. 18O-exchange dependence on bivalent cation and nucleotide nature is found. The comparison of 18O-exchange characteristics for myosins of smooth and skeletal muscles confirms the hypothesis on the similarity of molecular mechanisms of ATP hydrolysis by myosin from different muscle types.

[Oxygen isotope exchange reactions in synaptosomal plasmatic membrane system]. / Reaktsii izotopnogo obmena kisloroda neorganicheskogo fosfata v sisteme plazmaticheskikh membran sinaptosom.

Mg2+-Dependent, Ca2+-activated adenosine triphosphatase (E. C. 3.6.1.4) of synaptosomal plasmatic membrane from cow brain catalyses isotopic exchange of oxygen atoms: KH2P18O 4 in equilibrium H2O, the degree of exchange depending on Ca2+ concentration. The 18O-exchange catalysis suggests that the enzyme under consideration acts as a transport ATPase.

18O-exchange catalyzed by myosin, heavy meromyosin, heavy meromyosin subfragment 1 and their complexes with actin.

Myosin, HMM and HMM S1 catalyze 18O-exchange between P1 and H218O of the medium at an intermediate stage of ATP hydrolysis ("intermediate 18O-exchange") in the presence of Mg2+. Natural complexes of actomyosin and acto-HMM S1 do not catalyze intermediate 18O-exchange but facilitate "direct" or "medium" 18O-exchange (KH2P18O4 in equilibrium H2O) even without ATP. Reconstituted complexes of actomyosin, acto-HMM, acto-HMM S1, PABC-HMM S1, congo-myosin and TNP-myosin do not catalyze direct 18O-exchange in the presence of Mg2+ and absence of ATP. From the data obtained a hypothetical sequence of phosphorylation and 18O-exchange reactions in myofibril action has been suggested.

[18 O-exchange reactions catalyzed by subfragment 1 of myosin molecule]. / O18-obmennye reaktsii, kataliziruemye subfragmentom 1 molekuly miozina

18 O-exchange properties of enzymically active proteolytic fragment of myosin molecule--subfragment 1 were studied. It was shown that 18O-exchange activity of subfragment 1 is similar to that of parental myosin and its other proteolytic fragment--heavy meromyosin. The experimental data suggest that the 18O-exchange activity is an integral property of myosin and is not determined by its contaminations.