N-Terminal Fragment of Cardiac Myosin Binding Protein-C Increases the Duration of Actin-Myosin Interaction.

Cardiac myosin binding protein-C (cMyBP-C) located in the C-zone of myocyte sarcomere is involved in the regulation of myocardial contraction. Its N-terminal domains C0, C1, C2, and the m-motif between C1 and C2 can bind to the myosin head and actin of the thin filament and affect the characteristics of their interaction. Measurements using an optical trap showed that the C0-C2 fragment of cMyBP-C increases the interaction time of cardiac myosin with the actin filament, while in an in vitro motility assay, it dose-dependently reduces the sliding velocity of actin filaments. Thus, it was found that the N-terminal part of cMyBP-C affects the kinetics of the myosin cross-bridge.

Comparison of Functional Characteristics of Myosin in Fast and Slow Skeletal Muscles.

Myosins of fast and slow skeletal muscles differ by the isoform composition of the heavy and light chains. We compared functional characteristics of myosin from the fast (m. psoas) and slow (m. soleus) muscles of rabbits. The parameters of single actin-myosin interaction were measured in an optical trap, and the characteristics of the Ca2+ regulation of actin-myosin interaction were studied using an in vitro motility assay. The duration of interaction of myosin from the fast muscle with actin was shorter and the filament sliding velocity over this myosin was higher than the corresponding parameters for myosin from the slow muscle. The dependence pCa-velocity for myosin from the fast muscle was less sensitive to Ca2+ than that of slow muscle myosin. Thus, functional properties of myosin determine not only mechanical and kinetic characteristics of muscle contraction, but also the peculiarities of its Ca2+ regulation.

Carbonylation of atrial myosin prolongs its interaction with actin.

Carbonylation induced by hyperthyroidism suppresses force generation of skeletal myosin and sliding velocity of actin filaments in an in vitro motility assay. However, its effects on cardiac myosin at the molecular level have not been studied. Hyperthyroidism induces a change in expression of myosin heavy chains in ventricles, which may mask the effect of oxidation. In contrast to ventricular myosin, expression of myosin heavy chains in the atrium does not change upon hyperthyroidism and enables investigation of the effect of oxidation on cardiac myosin. We studied the influence of carbonylation, a type of protein oxidation, on the motor function of atrial myosin and Ca2+ regulation of actin-myosin interaction at the level of isolated proteins and single molecules using an in vitro motility assay and an optical trap. Carbonylation of atrial myosin prolonged its attached state on actin and decreased maximal sliding velocity of thin filaments over this myosin but did not affect the calcium sensitivity of the velocity. The results indicate that carbonylation of atrial myosin induced by hyperthyroidism can be a rate-limiting factor of atrium contractility and so participates in the genesis of heart failure in hyperthyroidism.

The properties of the actin-myosin interaction in the heart muscle depend on the isoforms of myosin but not of α-actin.

In myocardium of mammals there are two isoforms of myosin heavy chains, α and ß. In ventricle, together with ventricular isoforms of light chains they form two isomyosins: V1 and V3, homodimers of α- and ß-heavy chains, respectively. In atria, α- and ß-heavy chains together with atrial light chains form A1 (αα) and A2 (ßß) isomyosins. Besides in myocardium two isoforms of α-actin, skeletal and cardiac, are expressed. We assume that the differences in the amino acid sequence of cardiac and skeletal actin may affect its interaction with myosin. To test this hypothesis, we investigated characteristics of actin-myosin interactions of cardiac and skeletal isoforms of α-actin with the isoforms of cardiac myosin using an optical trap technique and an in vitro motility assay. It was found that the mechanical and kinetic characteristics of the interactions of the isoforms of cardiac myosin with actin depend on the isoforms of myosin not α-actin.

Investigations of Molecular Mechanisms of Actin-Myosin Interactions in Cardiac Muscle.

The functional characteristics of cardiac muscle depend on the composition of protein isoforms in the cardiomyocyte contractile machinery. In the ventricular myocardium of mammals, several isoforms of contractile and regulatory proteins are expressed - two isoforms of myosin (V1 and V3) and three isoforms of tropomyosin chains (α, ß, and κ). Expression of protein isoforms depends on the animal species, its age and hormonal status, and this can change with pathologies of the myocardium. Mutations in these proteins can lead to cardiomyopathies. The functional significance of the protein isoform composition has been studied mainly on intact hearts or on isolated preparations of myocardium, which could not provide a clear comprehension of the role of each particular isoform. Present-day experimental techniques such as an optical trap and in vitro motility assay make it possible to investigate the phenomena of interactions of contractile and regulatory proteins on the molecular level, thus avoiding effects associated with properties of a whole muscle or muscle tissue. These methods enable free combining of the isoforms to test the molecular mechanisms of their participation in the actin-myosin interaction. Using the optical trap and the in vitro motility assay, we have studied functional characteristics of the cardiac myosin isoforms, molecular mechanisms of the calcium-dependent regulation of actin-myosin interaction, and the role of myosin and tropomyosin isoforms in the cooperativity mechanisms in myocardium. The knowledge of molecular mechanisms underlying myocardial contractility and its regulation is necessary for comprehension of cardiac muscle functioning, its disorders in pathologies, and for development of approaches for their correction.

Response of the photosynthetic apparatus of cotton (Gossypium hirsutum) to the onset of drought stress under field conditions studied by gas-exchange analysis and chlorophyll fluorescence imaging.

The functioning of the photosynthetic apparatus of cotton (Gossypium hirsutum) grown during the onset of water limitation was studied by gas-exchange and chlorophyll fluorescence to better understand the adaptation mechanisms of the photosynthetic apparatus to drought conditions. For this, cotton was grown in the field in Central Asia under well-irrigated and moderately drought-stressed conditions. The light and CO(2) responses of photosynthesis (A(G)), stomatal conductance (g(s)) and various chlorophyll fluorescence parameters were determined simultaneously. Furthermore, chlorophyll fluorescence images were taken from leaves to study the spatial pattern of photosystem II (PSII) efficiency and non-photochemical quenching parameters. Under low and moderate light intensity, the onset of drought stress caused an increase in the operating quantum efficiency of PSII photochemistry (varphi(PSII)) which indicated increased photorespiration since photosynthesis was hardly affected by water limitation. The increase in varphi(PSII) was caused by an increase of the efficiency of open PSII reaction centers (F(v)'/F(m)') and by a decrease of the basal non-photochemical quenching (varphi(NO)). Using a chlorophyll fluorescence imaging system a low spatial heterogeneity of varphi(PSII) was revealed under both irrigation treatments. The increased rate of photorespiration in plants during the onset of drought stress can be seen as an acclimation process to avoid an over-excitation of PSII under more severe drought conditions.

[Optical trap as a tool for studying motor proteins].

The review is concerned with the optical trap method, a modern experimental tool based on the recently discovered ability of light to trap and hold micron and submicron particles in the focused beam. The physical principle of operation of the optical trap and the possibilities of using the tool in studies of the molecular nature of biological motility have been considered. Some studies devoted to the physical characteristics and functioning of single molecules of motor proteins have been analyzed that have been performed with the optical trap method, which allows one to record nanometer displacements and piconewton forces.

Raman study of molecular dynamics of inorganic fluoroxidizers in nonaqueous solutions: part 4. Xenon tetrafluoride and xenon hexafluoride in hydrogen fluoride.

Raman spectra of XeF4 and XeF6 in the nonaqueous HF solutions at various concentrations and vibrational spectra of the [XeF5]+ cation in the solid state and in the HF solutions over a wide range of vibrational frequencies have been studied. The assignments of the observed vibrational bands of the [XeF5]+ cation and XeF6-HF system has been made. A number of associates or solvates being formed as a result of the donor-acceptor interaction between Lewis base and Lewis acid has been shown to exist alongside with ionized monomeric and polymeric modifications of XeF6 in the HF solution such as ([XeF5]+ F-)n (n = 1, 2, 4). The contours of the nu1(A1g) band of XeF4 with frequency 552 cm(-1) and bands of stretching modes of ([XeF5]+ F-)n (n = 1, 2, 4) with frequency in the range of 600-670 cm(-1) are analysed. The correlation functions of the vibrational and rotational relaxation as well as the corresponding characteristic time for these processes have been calculated. A conclusion has been driven at that it is vibrational dephasing that makes the major contribution to the formation of ([XeF5]+ F)4 and ([XeF5]+ F-)2 band contours, while in the case of [XeF5]+ F- and XeF4 the contributions of vibrational dephasing and rotational relaxation nearly coincide.

[Use of pervomur for irrigation of purulent cavities]. / Primenenie pervomura dlia sanatsii gnoinykh polostei.

Experimentally it has been shown that diluted Pervomur (1:3) may be used for the intraoperation washing of the pleural cavity. The use of the diluted drug during the operations for acute purulent diseases of the lungs and pleura made it possible to prevent postoperative pleural empyemas and suppluration of soft tissue wounds in most patients.

[Hemodynamic and functional changes in the liver of children with extrahepatic portal hypertension in relation to the method of portacaval shunt]. / Gemodinamicheskie i funktsional'nye izmeneniia pecheni u detei s vnepechenochnoi portal'noi gipertenziei v zavisimosti ot metoda portokaval'nogo shuntirovaniia.

Scintihepatographic investigations with colloid 99mTc before and after operations in 4 groups of children were performed: with cavo- or ileomesenterial anastomosis, with splenorenal anastomosis with splenectomy and cavo- or ileomesenterial anastomoses in children with previously performed splenectomy and in a group of comparison. Perfusion of the liver was found to decrease: in the least degree after splenorenal anastomosis and in the greater degere after cavo- and ileomesenterial one. It was established that all kinds of shunts ensured function of hepatocytes.