Moderately thermophilic nitrifying bacteria from a hot spring of the Baikal rift zone

Samples from three hot springs (Alla, Seya and Garga) located in the northeastern part of Baikal rift zone (Buryat Republic, Russia) were screened for the presence of thermophilic nitrifying bacteria. Enrichment cultures were obtained solely from the Garga spring characterized by slightly alkaline water (pH 7.9) and an outlet temperature of 75 degrees C. The enrichment cultures of the ammonia- and nitrite oxidizers grew at temperature ranges of 27-55 and 40-60 degrees C, respectively. The temperature optimum was approximately 50 degrees C for both groups and thus they can be designated as moderate thermophiles. Ammonia oxidizers were identified with classical and immunological techniques. Representatives of the genus Nitrosomonas and Nitrosospira-like bacteria with characteristic vibroid morphology were detected. The latter were characterized by an enlarged periplasmic space, which has not been previously observed in ammonia oxidizers. Electron microscopy, denaturing gradient gel electrophoresis analyses and partial 16S rRNA gene sequencing provided evidence that the nitrite oxidizers were members of the genus Nitrospira.     

Participation of granulosa cells in mediation of prolactin and somatotropin action on bovine oocyte-cumulus complexes in vitro

Maturation of bovine oocyte-cumulus complexes (OCC) in media derived following granulosa cell culturing with prolactin (PRL, 50 ng/ml) and somatotropin (ST, 10 ng/ml) was studied. A medium conditioned by granulosa cells in the presence of PRL or ST exerted a stimulating effect on the proliferative activity of cumulus cells. ST introduction into the granulosa cell culture also caused a decrease in the rate of cumulus cells with degenerated chromatin at a subsequent OCC culturing. At the same time, the expansion of cumulus did not depend on hormone availability in the culture medium for granulosa cells. When OCC matured in conditioned media, a short-term inhibition of oocyte meiosis reinitiation (after 6 h of culturing) was revealed in both the experimental groups, as compared to the control. Furthermore, the addition of ST and PRL to granulosa cell culture resulted in a subsequent decline in the rate of oocytes with signs of chromosome degeneration, observed as early as by 6 h of incubation and to be retained throughout the whole period of OCC culturing. In this case the earlier resumption of meiosis was associated with a higher rate of degeneration of the nuclear material in oocytes. The results of the present study suggest that granulosa cells may mediate, at least in part, PRL and ST impacts on in vitro maturation of bovine OCC, with no contact between OCC and granulosa cells being required for hormonal signaling.     

Mitosis: regulation and organization of cell division

Modern views on genetic, cytological and molecular bases of the structure and regulation of preparing and implementing mitotic chromosome segregation are discussed.     

Kinetic model of imidazologlycerol-phosphate synthetase from <Emphasis Type="Italic">Escherichia coli</Emphasis>

Based on the available experimental data, we developed a kinetic model of the catalytic cycle of imidazologlycerol-phosphate synthetase from Escherichia coli accounting for the synthetase and glutaminase activities of the enzyme. The rate equations describing synthetase and glutaminase activities of imidazologlycerol-phosphate synthetase were derived from this catalytic cycle. Using the literature data, we evaluated all kinetic parameters of the rate equations characterizing individually synthetase and glutaminase activities as well as the contribution of each activity depending on concentration of the substrates, products, and effectors. As shown, in the presence of 5 -phosphoribosylformimino-5-aminoimidazolo-4-carboxamideribonucleotide (ProFAR) and imidazologlycerol phosphate (IGP) glutaminase activity dominates over synthetase activity at sufficiently low concentrations of 5 -phosphoribulosylformimino-5-aminoimidazolo-4-carboxamideribonucleotide (PRFAR). Increased PRFAR concentrations resulted in decreased contribution of glutaminase activity and, consequently, increased the contribution of synthetase activity in the enzyme functioning.     

A kinetic model of the cytochrome bf complex. Evaluation of kinetic parameters

A kinetic model of the cytochrome bf complex was developed on the assumption that the Q-cycle operates. The bf complex was considered as a membrane enzyme catalyzing the electron transfer from plastoquinol to plastocyanine, which is coupled with proton translocation from the chloroplast stroma to the thylakoid lumen. The dependence of the electron transfer rates on the value of the transmembrane electric potential was taken into account. The model was applied to describe the experimental data on the flash-induced turnover of cytochromes b, plastocyanine, and the kinetics of proton deposition in the thylakoid lumen. The estimation of model parameters was performed.     

Characterization of growth hormone binding sites in granulosa and theca layers at different stages of follicular maturation and ovulatory cycle in the domestic hen

The currently available evidence points to a possible influence of growth hormone (GH) on avian folliculogenesis, which can be mediated by both hepatic- and ovarian-derived IGF-I. Therefore, the purpose of the present study was to reveal GH-binding sites in granulosa and theca layers of preovulatory follicles and to determine the binding characteristics depending on the degree of follicular maturation and the stage of the ovulatory cycle in the hen. Hens were killed 2 h (stage I), 9 h (stage II), 16 h (stage III), and 23 h (stage IV) after oviposition, and the five largest yellow follicles (from F1 to F5) were removed. GH-binding sites in granulosa and theca layers from F1 to F5 follicles were characterized using a radioreceptor assay. Equilibrium dissociation constants (K(d)) and binding capacities (B(max)) were determined by Scatchard analysis of saturation curves, which revealed a single class of high-affinity GH-binding sites in both theca tissue and granulosa cells. In F1, F2, and F5 follicles, B(max) and K(d) for GH-binding sites in the granulosa layer changed during the ovulatory cycle, decreasing between stages I and III, to increase again at stage IV, with alterations in K(d) being less profound. No significant differences in binding capacities and affinities of GH-binding sites in the theca layer were found between various stages of the cycle. Furthermore, the concentration of GH-binding sites in the granulosa layer rose, whereas that in the theca layer fell with follicular enlargement. These findings indicate the presence of high-affinity GH-binding sites in both granulosa and theca layers of hen preovulatory follicles. Data also demonstrate that GH-binding sites in these tissues are regulated in a tissue-specific manner. Furthermore, the regulation of binding capacity of GH binding in granulosa cells by hormonal factors associated with ovulatory cycle is apparently not dependent on the state of follicular maturation.