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871.
Comparative bioenergetics of sulfate reduction in Desulfovibrio and Desulfotomaculum spp. 总被引:2,自引:0,他引:2 下载免费PDF全文
Extracts of Desulfotomaculum nigrificans, Desulfotomaculum orientis, and Desulfotomaculum ruminis exhibit low levels of inorganic pyrophosphatase but were found to have high levels of pyrophosphate:acetate phosphotransferase. Conversely, extracts of Desulfovibrio gigas, Desulfovibrio vulgaris, and Desulfovibrio desulfuricans Norway 4 were shown to have high levels of inorganic pyrophosphatase but negligible amounts of pyrophosphate:acetate phosphotransferase. Both enzymes are reductant activated and appear to have an analogous function in removing pyrophosphate formed during the activation of sulfate. Conservation of the bond energy of pyrophosphate in Desulfotomaculum eliminates the necessity for invoking electron-transfer-coupled phosphorylation to account for the growth of these bacteria on lactate plus sulfate. Relative growth yields of Desulfovibrio vulgaris and Desulfotomaculum orientis on lactate plus sulfate indicate that the latter does not carry out significant electron-transfer-coupled phosphorylation in this mode of growth. 相似文献
872.
Role of cyclic AMP-dependent protein kinase in the induction of tyrosine aminotransferase 总被引:2,自引:0,他引:2
A Y Liu 《The Journal of biological chemistry》1980,255(10):4421-4429
873.
874.
A unique ribonuclease, active only in the presence of Ca2+, was present in lactating mammary gland and milk of the rat. This enzyme was absent from virgin-rat mammary gland and non-mammary tissues of lactating rats. The presence of moderate activity in differentiated mammary tumours, together with an increase in activity in normal tissue parelleling development of mammary function, identify this enzyme as a marker of mammary differentiation in the rat. 相似文献
875.
Polarization of chlorotetracycline fluorescence in pancreatic islet cells and its response to calcium ions and D-glucose. 下载免费PDF全文
Suspensions rich in pancreatic beta-cells were prepared from non-inbred ob/ob-mice, incubated with 10 micrometer-chlorotetracycline, and analysed for fluorescence polarization in a microscope. Throughout the temperature range 16--38 degrees C, fluorescence was enhanced by 5 mM-Ca2+ in the incubation medium; 20 mM-D-glucose decreased the fluorescence measured in the presence of Ca2+. Fluorescence showed a curvilinear negative regression on temperature. The curves were rectified to a virtually ideal degree by Arrhenius transformations of data. Non-parametric testing of differences between linearized regression lines forms the basis for the following conclusions. The temperature-dependence of fluorescence intensity appeared to be smaller for Ca2+-specific signals than for the background fluorescence of chlorotetracycline in Ca2+-deficient cells. D-Glucose significantly diminished the polarization of fluorescence in cells incubated with Ca2+. It is suggested that D-glucose increases the mobility of Ca2+ in beta-cell plasma membranes; this mobility increase may help to explain previously reported effects of D-glucose on 45Ca2+ fluxes and membrane electric potential. 相似文献
876.
Su-Chin C. Liu Mary J. Eaton Marvin A. Karasek 《In vitro cellular & developmental biology. Plant》1979,15(10):813-822
Summary Using gels of acid-soluble, collagen as a culture surface, trypsin-released keartinocytes from 0.1-mm, split-thickness sections
of newborn foreskin may be plated with high efficiency and subcultured at a 1∶5 split a 2- to 3-week intervals for three subpassages.
When plated at a density of 3.2×104 cells per cm2, keratinocytes attach to the gel with an efficiency of over 70%; after a lag phase of 3 days, the cells multiply exponentially
with a doubling time of 60 hr. Cultures reach a growth-plateau phase at a density of 47.7×104 cells per cm2. Both hydrocortisone and epidermal growth factor (EGF) stimulate slightly the growth of primary cultures; both factors are
required for proliferation of the 2nd and further passage of keratinocytes. As the cultures reach, confluence multilayers,
of stratified cells are formed and cells of squamous morphology are spontaneously released from the surface. When the released
cells and the attached cells are pulsed with [3H]-histidine and [14C]-leucine, a higher ratio of histidine to leucine is observed in the released cells indicating the biochemical onset of maturation.
Orange G-Aniline Blue staining of the released cells show some of the cells to be completely keratinized. Fibrous proteins
extracted from the cultured cells and analyzed by sodium dodecyl sulfate (SDS) gel electrophoresis display the characteristic
stratum corneum proteins of 60,000 and 66,000 daltons.
Supported in part by Grants AM 14121 and AM 19595 of the U.S. Public Health Service. 相似文献
877.
British Anti-Lewisite (BAL) binds to horseradish peroxidase in a manner which results in inhibition of both peroxidatic and oxidative functions of the enzyme. BAL competes with hydrogen peroxide for binding on peroxidase, and the inhibition of peroxidatic activity is irreversible. Solutions of purified horseradish peroxidase and individually resolved peroxidase isozymes show a gradual loss of peroxidatic activity with time when incubated with BAL. In these same treatments, however, the inhibition of indole-3-acetic acid (IAA) oxidase activity is immediate. With increasing amounts of enzyme in the incubation mixture, IAA oxidase activity is not completely inhibited and is observed following a lag period in the assay which shortens with longer incubation times. Peroxidase activity during this same time interval shows a lag period which increases with longer incubation times. Lowering the pH removed the lag period for oxidase activity, but did not change the pattern of peroxidase activity. These results suggest that the sites for the oxidation of indole-3-acetic acid and for peroxidatic activity may not be identical in horseradish peroxidase isozymes. 相似文献
878.
879.
880.
The enzyme tyrosinase (E.G. 1.14.18.1) has been immobilized in a polyacrylamide gel and intermittently assayed for enzyme activity over a period of 19 days using phenol as the substrate. The results of these studies indicate that the immobilized enzyme could be incorporated into a system to detect phenol and related compounds that are found in industrial effluents and as surface water contaminants. 相似文献