[Irregular activity oscillations of rotary molecular motor. A simple kinetic model of F1-ATPase].

F1-ATPase is a catalytic portion of the rotary molecular motor, F1Fo-ATP synthase. Cooperative ATP hydrolysis at the three catalytic sites of the F1-ATPase is connected with rotation of the central gamma-subunit inside a cylinder made of three a subunits and three beta subunits. Various experimental works have shown that the gamma-subunit rotates with irregular dwells. A simple kinetic model of this paper explains dwells during rotation as a result of the deterministic chaos. It is shown that the deterministic chaos occurs under the rate constants close to the known experimental estimations. Time duration of dwells in the model are close to those observed experimentally. Our model explains the known irregular occupancy of catalytic sites of F1-ATPase by nucleotides.

[A simple kinetic model for dynein oscillatory activity].

A kinetic model for dynein, a molecular motor, complexed with microtubule fragments, is considered. The model explains the experimental observations of oscillatory movements in surprisingly simple axonemal fragments perfused by the ATP solution. The model explains at first time the oscillatory dynein activity as a phenomenon induced by two dynein heads cooperative interaction in the axoneme. The oscillation form, frequency, and amplitude, observed for the model, are close to these experimental characteristics. Kinetic parameters, used in the model, are close to the known experimental parameters.

[Calmodulin can induce and control damping oscillations in the plasma membrane Ca2+ -ATPase activity: a kinetic model].

Plasma membrane Ca2+-ATPase is the calcium pump that extrudes calcium ions from cells using ATP hydrolisis for the maintenance of low Ca2+ concentrations in the cell. Calmodulin stimulates Ca2+-ATPase by binding to the autoinhibitory enzyme domain, which allows the access of cytoplasmic ATP and Ca2+ to the active and transport cites. Our kinetic model predicts damped oscillations in the enzyme activity and interprets the known nonmonotonous kinetic behavior of the enzyme in the presence of calmodulin. For the parameters close to the experimental ones, the kinetic model explains the changes in frequency and damping factor of the oscillatory enzyme activity, as dependent on calmodulin concentration. The calculated pre-steady-state curves fit well the known experimental data. The kinetic analysis allows us to assign Ca2+-ATPase to the hysteretic enzymes exhibiting activity oscillations in open systems.

[The inflow of the substrate can regulate the persistence of memory of enzymes having the properties of hysteresis: theoretical analysis].

A simple kinetic model of hysteretic enzymes with the influx of substrate or ion (transported by the enzyme) is considered. Two alternative steady activity levels are shown to arise in the system with a hysteretic enzyme. The transition between these levels can proceed in an oscillatory manner. The duration of the initial steady activity level is shown to be determined by the initial substrate (or ion) level, and the oscillatory transition between the activity levels is the property of hysteretic enzymes. It was shown for plasma membrane Ca2+-ATPase as an example that the level of the signal can be encoded into the time interval in which the enzyme retains the memory about this signal.

[Association of proteinases with histones from rat thymus nuclei]. / Assotsiatsiia proteinaz s gistonami iader timusa krys.

Histone H2A, H2B, and H1--specific proteinases tightly associated with histones were shown to be present in rat thymus nuclei. The activity of proteinases tightly associated with histones increases after exposure of animals to gamma-rays. The denatured DNA activated the histone H1-specific proteinase. These proteinase dissociated from histones in the presence of dithiothreitol. The histones and proteinases were divided into fractions by chromatography on DEAE-cellulose in the presence of 5 mM dithiothreitol.

[Structure-activity relationships in multienzyme complexes]. / Strukturno-funktsional'nye otnosheniia v mul'tifermentnykh kompleksakh.

Structures and molecular kinetic models of function of 2-oxo acid dehydrogenase complexes were analyzed. It was suggested that identical protein subunits in the multienzyme complexes as in the structure capable of self-assembly have identical contacts with the neighbors and identical environment. By sharing the enzyme aggregate subunits into distinct conformational classes the peripheral components were demonstrated to be arranged on the core so that the entire complex would have a definite symmetry. The number of the conformational classes is specified by the architecture of the core and considerations of symmetry. The results have allowed us to consider the mechanisms of functioning of the complexes. Specific examples are discussed.

[Degradation and repair of rat hepatoma cell DNA following exposure to gamma rays and methylnitrosourea]. / Degradatsiia i reparatsiia DNK kletok gepatomy krys posle deistviia gamma-luchei i metilnitrozomocheviny.

Single-strand breaks induced in DNA of ascitic hepatoma cells by gamma-rays and N-methyl-N-nitrosourea (MNU), resp., may be effectively repaired. Double-strand breaks of DNA from MNU-treated hepatoma cells are also effectively repairable in vivo. Only a small part of double-strand breaks induced by gamma-rays in DNA of these cells is repaired in the postradiation period. The combined action of gamma-rays and MNU on the hepatoma cells causes a complete inhibition of repair of DNA and its further degradation. Under these conditions, inhibition of the repair of DNA synthesis and repression of DNA polymerase I activity is observed.

[A comparative study of the DNA structural damages and synthesis in embryos of the silkworm Bombyx mori irradiated with gamma rays at different developmental stages]. / Sravnitel'noe issledovanie strukturnykh povrezhdenii i sinteza DNK v émbrionakh tutovogo shelkopriada Bombyx mori, obluchennykh gamma-luchami na raznykh stadiiakh razvitiia.

Studies have been made on formation and reparation of apurine-apyrimidine (AP) regions, monothread DNA ruptures, as well as on inhibition and recovery of DNA synthesis in gamma-irradiated 3- and 7-day embryos of the silkworm which sharply differ in their radiosensitivity. It was shown that in 3-day embryos, the number of AP regions and DNA ruptures immediately after irradiation is significantly higher than in 7-day embryos. DNA synthesis is more radiosensitive in 3-day embryos as compared to that in 7-day ones. Kinetics of postradiation recovery of regions and DNA ruptures in 3- and 7-day embryos is heterogeneous and significantly different. However, radiation inhibition and postradiation recovery of DNA synthesis in irradiated 3- and 7-day embryos are associated mainly with postradiation survival of these embryos.

[The effect of proteinase inhibitors on the level of degradation and unscheduled synthesis of DNA in ultraviolet- and gamma-irradiated cellsof mouse ascitic carcinoma]. / Vliianie ingibitorov proteinaz na uroven' degradatsii i nezaplanirovannogo sinteza DNK v UF- i gamma-obluchennykh kletkakh astsitnoi kartsinomy myshei.

Proteinase inhibitors (e.g. antipain, pepstatin A, and phenylmethane sulfonyl fluoride) were shown to decrease the rate of incision DNA degradation and the level of unscheduled synthesis of DNA in Ehrlich ascites tumor cells exposed to UV-light and gamma-radiation. The results obtained indicate that nuclear proteinases are involved in regulation of DNA repair process.

[DNA-protein complexes of the nuclear matrix of Ehrlich ascites carcinoma cells]. / DNK-belkovye kompleksy iadernogo matriksa kletok astsitnoi kartsinomy Erlikha.

A DNA-protein complex resistant to 8 M urea and 0.1% SDS was obtained by chromatography of nuclear matrix lysate from Ehrlich ascite carcinoma cells on Sepharose 2BCL. Separation of the complex under more severe conditions (4 M guanidine hydrochloride, 5 M urea) on hydroxylapatite resulted in protein and DNA fractions, as well as in two fractions of the DNA-protein complex. One of the fractions of this complex was enriched with single-stranded DNA and contained a 5-fold excess of newly synthesized DNA over the DNA present in the original complex. The fractions isolated from the nuclear matrix of control Ehrlich ascite carcinoma cells and the cells incubated with novobiocin revealed quantitative and qualitative differences in the electrophoretic patterns of the proteins. Treatment of cells with novobiocin resulted in inhibition of DNA replicative synthesis and an increase in the protein/DNA ratio in the nuclear matrix.

[Hydrocortisone and partial hepatectomy activate a proteinase associated with histones]. / Gidrokortizon i chastichnaia gepatéktomiia aktiviruiut proteinazu, assotsirovannuiu s gistonami.

Proteinase activity has been shown to be associated with histones of rat thymus and liver nuclei. Hydrocortisone increases the activity of proteinases associated with thymus nuclear histones. Increasing activity of histone-associated proteinases is also observed during intensive transcription and replication in regenerating rat liver.

[Proteins firmly bound to DNA in the E. coli nucleoid]. / Prochno sviazannye s DNK belki v sostave nukleoida E. coli.

The nucleoid isolated from E. coli cells was subjected to further deletion by treatment with 2 M NaCl. After disintegration of this nucleoid by ultrasonication, two fractions were obtained, i. e., a rapidly (RS) and slowly sedimenting (SS) ones. The protein, RNA and DNA patterns in the RS fraction are similar to that of the eukaryotic cell nuclear matrix. Electrophoretic analysis of total non-dissociating by 2 M NaCl proteins revealed that the RS and SS fractions predominantly contain proteins with Mr 31,27 and 23 kD. The protein with Mr = 31 kD is firmly bound to DNA, does not dissociate in the guanidine hydrochloride (4 M)-urea (5 M) mixture as well as in solution of 1% sodium-dodecyl sulphate and may be responsible for the chromosome binding to the E. coli membrane.

[Effect pf protease inhibitors on DNA degradation in gamma-irradiated rat thymocytes]. / Vliianie ingibitorov proteaz na degradatsiiu DNK v gamma-obluchennykh timotsitakh krys.

Protease inhibitors, antipain and pepstatin, decrease the postirradiation degradation of DNA in gamma-irradiated rat thymocytes. It is suggested that a protease-dependent process of induction of DNA breaks takes place in irradiated cells.