[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.

[Effect of pH on ATPase activity and 18-O metabolism catalyzed by membrane preparations of Na,K-ATPase from guinea pig kidneys]. / Vliianie pH na ATFaznuiu aktivnost' i 180-obmen, kataliziruemye membrannymi preparatami na,K-ATPazy iz pochek morskoi svinki.

The effect of pH in the incubation medium on ATPase activity and the direct 18O-exchange, catalyzed by initial and treated by surface active agents membrane preparations of Na, K-ATPase has been studied. The pH dependence of the ratio between the direct 18O exchange and Na,K-ATPase activity was detected; this ratio being equal to 4,5 +/- +/- 0.6, 1.5 +/- 0.1 and 0.4 +/- 0.1 at the pH values of 6.1, 7.5 and 9.0, respectively. The pretreatment of preparations by DOC or histone H2a, used in both activatory and inhibitory-amounts, abolished the effect of acid pH and made the ratio practically the same at 6.1 and 7.5 pH values. Both agents did not affect the action of the alcaline pH value equal to 9.0. Triton X-100 was not able to change the pH dependence of the ratio.

[Light-induced changes in activity of Na, K-ATPase from the retinal photoreceptors of vertebrates: possible mechanism]. / Izmenenie aktivnosti Na, K-ATPazy fotoretseptorov setchatki pozvonochnykh pro osveshchenii: vozmozhnyi mekhanizm.

The mechanism of light-induced changes in the activity of Na,K-ATPase from plasma membranes (PM) of photoreceptor cells was studied in vitro. Illumination resulted in inhibition of the ATPase activity and an increase of 18O exchange between water and Pi. The maximum light effect was revealed when the PM contained both the inner segments of the rods (RIS) and rod outer segments (ROS) of the photoreceptor cells. Lipid peroxidation stimulated by the FeSO4+ascorbate system induced a decrease of the ATPase activity. Antioxidants (ionol, Na2SeO3, vitamin E) prevented the effect of the lipid peroxidation products on NA,K-ATPase and the photoinduced changes of the enzyme activity. It is supposed that the photoinduced changes of the Na,K-ATPase activity in vitro are due to lipid peroxidation of photoreceptor PM.

[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.

[Effect of surface-active agents on Na, K-ATPase from guinea pig kidneys]. / Vliianie poverkhnostno-aktivnykh veshchestv na Na, K-ATFazu iz pochek morskoi svinki.

The effect of surface active agents on the activity of Na, K-ATPase and on the direct medium 18O exchange in the membrane preparations of the guinea pig kidney has been studied. The medium 18O exchange was considered as a character of the K+-dependent stage in ATPase reaction. Low concentration of all the surface active agents were shown to stimulate, and high concentrations -- to inhibit both ATPase and medium 18O exchange. The relation between medium 18O exchange and Na,K-ATPase activity was found to be equal to 1.5 +/- 0.1. The treatment of preparations by activating amounts of the surface active agents resulted in lowering this relation up to 1.0 +/- 0.09 and 1.3 +/- 0.04 for DOC and triton X-100, correspondently, due to a stronger stimulation of ATPase activity than of medium 18O exchange. With the inhibiting amounts of triton X-100 and histone H2a, this relation did not change, but it decreased in the presence of equal amounts of DOC.

[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.

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.