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31.
Kurt Ahrn Ensio Norjavaara Sten Rosberg Gunnar Selstram 《Prostaglandins & other lipid mediators》1983,25(6):839-851
Epinephrine can mimic the stimulatory effects of LH in vitro on cyclic AMP (cAMP) and progesterone production by isolated rat corpora lutea. The aim of the present study was to test whether the effects of epinephrine in vitro on the rat corpus luteum, as with LH, can be inhibited by prostaglandin F2a (PGF2a. The stimulatory effect of epinephrine on tissue levels of cAMP in 1-day-old corpora lutea was not inhibited by PGF2. A dose-dependent inhibition by PGF2a (0.5–50 μM) was seen for 3-day-old corpora lutea and this inhibition could not be overcome by higher concentrations of epinephrine (0.165–165 μM). The stimulation by epinephrine on progesterone production was inhibited by PGF2a (5 μM) in 3- and 5-day-old, but not in 1-day-old corpora lutea. Thus, PGF2a can inhibit the stimulatory effect of epinephrine in 3- and 5-day-old corpora lutea, but not in the newly formed corpora lutea (1-day-old) and PGF2a shows in this respect the same agedependent inhibitory pattern as in relation to LH stimulation. 相似文献
32.
We have studied the changes in the activities of both nitrogenase (switch off) and glutamine synthetase in Rhodospirillum rubrum upon addition of ammonium ions or glutamine to nitrogen fixing cultures. Both activities decrease drastically and return in a parallel manner when added ammonia is metabolized. The decrease in glutamine synthetase activity does not seem to be primarily due to adenylylation of the enzyme. Addition of glutamine to cells starved for nitrogen results in inactivation of glutamine synthetase but nitrogenase is only partially switched off.Abbreviations CeMe3NBr
Cetyltrimethylammonium bromide
- Hepes
N-2-hydroxyethyl-piperazine-N-2 sulfonic acid
- MSO
methionine-D,L-sulfoximine
- Tea-Dmg
triethanol amine-3,3-dimethylglutaric acid 相似文献
33.
The thyrotropin (TSH) producing cells are distributed in the rostral and proximal pars distalis. This cell type is the smallest and most infrequent cell of the adenohypophysis. Its cytology is similar to the smallest gonadotropic (GTH) cells although the two cell types can be separated by the size of the small secretory granules (diameter less than 200 nm) in the TSH cells. In presmolts and smolts the cells are more numerous than in parr and adult salmon and have cytological features indicating an increased activity. This was also the case after intraperitoneal injections of synthetic TRH. Antisera to carp GTH and salmon GTH cross-reacted with both the GTH and the TSH cells. Anti-human TSH cross-reacted only with the TSH cells which confirms the assumption of antigenic similarity between human and fish TSH. 相似文献
34.
The thermophilic blue-green alga Synechococcus lividus was grown at 38 and 55°C. The reaction center chlorophyll-protein complexes (CP) of Photosystem (PS I) and PS II, CP aI and CP aII, were isolated by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis at 4°C. SDS solubilization of thylakoids was performed in the temperature range 0–65°C. The low-temperature absorption and fluorescence emission spectral properties of the isolated chlorophyll-protein complexes were analyzed. Only traces of CP aI were solubilized at temperatures below the lipid phase transition temperature. Instead, a minor PS I component, CP a′I, was obtained that had absorption and fluorescence characteristics similar to those of CP aI. CP a′I had a slightly lower mobility than CP aI in SDS-polyacrylamide gel electrophoresis. The amount of CP aI in the gel scan profile increased dramatically when solubilization was carried out above the phase transition temperatures, but started to decrease above 60°C. CP aII, on the other hand, could be efficiently extracted even at 0°C and was stable in the scan profile up to extraction temperatures of 30–40°C. Low-temperature absorption and fluorescence emission spectra were typical for CP aI and CP aII and no specific effects of the two growth temperatures on these properties were observed. The phase transition temperature was considered to be critical for the solubilization of CP aI, either because of the difficulties of SDS (especially as it forms micelles at low temperatures) in penetrating the solidified membrane lipids at temperatures below that of the phase transition or because the CP aI monomers of the PS I antennae are so strongly bound to each other that they cannot be dissociated by SDS before thermal agitation has reached a certain level that is achieved above the phase transition temperature. We consider both the difficulties in solubilizing CP aI at sub-transition temperatures and the heat stability of the two complexes as adaptations which enable Synechococcus to grow under extreme high-temperature regimes. 相似文献
35.
36.
The distribution of copper and zinc among soluble proteins in liver from normal slaughter cattle was examined after gel filtration of the proteins. Gopper- and zinc-binding proteins were mainly separated into three fractions. Varying amounts of zinc were eluted in a fourth fraction of molecular weight less than 2,000. A clear relationship was noted between the amount of copper bound to the low molecular weight fraction (m.w. ~ 10,000) and the total liver zinc concentration. The high molecular weight protein fraction (m.w. > 65,000) dominated in liver with zinc concentrations below 40 µg/g wet weight and total copper concentrations from 16 to 240 µg/g, while in liver with zinc concentrations above 40 µg/g and copper concentrations ranging from 20 to 107 µg/g, the low molecular weight metallothionein-like fraction dominated. 相似文献
37.
38.
Inactivation of avian progesterone receptor binding to ATP-Sepharose by pyridoxal 5'-phosphate 总被引:1,自引:0,他引:1
H Nishigori V K Moudgil D Toft 《Biochemical and biophysical research communications》1978,80(1):112-118
The affinity of progesterone receptor from hen oviduct for ATP-Sepharose was diminished by preincubation with pyridoxal 5′-phosphate. This effect was specific for pyridoxal 5′-phosphate since the related compounds, pyridoxal, pyridoxine, pyridoxamine and pyridoxamine 5′-phosphate, were not effectors. The inactivation was easily reversed by the addition of the primary amine, Tris. However, in the presence of the reducing agent NaBH4, the inhibitory effect of pyridoxal 5′-phosphate was irreversible. The results suggest that pyridoxal 5′-phosphate forms a Schiff base with a critical amino group, presumably at the nucleotide binding site of the progesterone receptor. 相似文献
39.
40.
Nilsson J Persson B Von Heijne G 《Protein science : a publication of the Protein Society》2002,11(12):2974-2980
We have developed a method to reliably identify partial membrane protein topologies using the consensus of five topology prediction methods. When evaluated on a test set of experimentally characterized proteins, we find that approximately 90% of the partial consensus topologies are correctly predicted in membrane proteins from prokaryotic as well as eukaryotic organisms. Whole-genome analysis reveals that a reliable partial consensus topology can be predicted for approximately 70% of all membrane proteins in a typical bacterial genome and for approximately 55% of all membrane proteins in a typical eukaryotic genome. The average fraction of sequence length covered by a partial consensus topology is 44% for the prokaryotic proteins and 17% for the eukaryotic proteins in our test set, and similar numbers are found when the algorithm is applied to whole genomes. Reliably predicted partial topologies may simplify experimental determinations of membrane protein topology. 相似文献