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1.
C Bugnon D Lenys B Bloch D Fellmann 《Comptes rendus des séances de la Société de biologie et de ses filiales》1976,170(5):975-982
Immunocytological investigations have been performed on semi-thin sections of human fetal pituitaries ranging in fetal age from 6 to 26 weeks. Corticotrophs can be revealed by anti-ACTH (1-24), anti-ACTH (17-39) and anti-beta MSH but not by anti-alpha MSH immunesera from the 8th week. Somatotrophs are revealed with anti-human STH from 9th week. Differentiating cells containing only alpha subunits of glycoproteic hormones are present from 8th to 12th week. At 13th week beta subunits of TSH can be revealed immunocytologically in thyreotrophs. Beta subunits of LH or FSH can be detected in same gonadotrophic cells only from 15th week. 相似文献
2.
Metabolic transformation of cholestenediols 总被引:3,自引:0,他引:3
3.
The relationship of the postsynaptic 43K protein to acetylcholine receptors in receptor clusters isolated from cultured rat myotubes 总被引:17,自引:14,他引:3 下载免费PDF全文
We have examined the relationship of acetylcholine receptors (AChR) to the Mr 43,000 receptor-associated protein (43K) in the AChR clusters of cultured rat myotubes. Indirect immunofluorescence revealed that the 43K protein was concentrated at the AChR domains of the receptor clusters in intact rat myotubes, in myotube fragments, and in clusters that had been purified approximately 100-fold by extraction with saponin. The association of the 43K protein with clustered AChR was not affected by buffers of high or low ionic strength, by alkaline pHs up to 10, or by chymotrypsin at 10 micrograms/ml. However, the 43K protein was removed from clusters with lithium diiodosalicylate or at alkaline pH (greater than 10). Upon extraction of 43K, several changes were observed in the AChR population. Receptors redistributed in the plane of the muscle membrane in alkali-extracted samples. The number of binding sites accessible to an anti-AChR monoclonal antibody directed against cytoplasmic epitopes (88B) doubled. Receptors became more susceptible to digestion by chymotrypsin, which destroyed the binding sites for the 88B antibody only after 43K was extracted. These results suggest that in isolated AChR clusters the 43K protein covers part of the cytoplasmic domain of AChR and may contribute to the unique distribution of this membrane protein. 相似文献
4.
Glutamine synthetase (GS) from the chick brain was purified to apparent homogeneity by ammonium sulfate fractionation followed by affinity chromatography, electrofocusing and Sephadex G-150 chromatography. The purified enzyme showed a single band on sodium dodecyl sulfate analysis in polyacrylamide gel. By sedimentation equilibrium analysis and gel electrophoresis analysis, it was shown that the enzyme has a subunit molecular weight of 45,000 and a native molecular weight of 364,000, which is consistent with an octameric structure. Sedimentation analysis in the presence of Mg2+ revealed three different forms of macromolecules corresponding respectively to a monomer, a tetramer and an octamer. Among eight cations tested (Ca2+, Co2+, Fe2+, Li+, Mg2+, Mn2+, Ni2+, Zn2+) only Co2+, Mg2+ and Mn2+ supported GS activity; the order of activatory ability was Mg2+>Co2+>Mn2+. The maximum activating effect of Mn2+ occurs only within a very narrow range of concentration: with an excess of cation causing strong inhibition of GS activity. For each cation, maximal GS activity occurs at a defined cation/ATP ratio. A regulatory system in which Mn2+, modulates the Mg2+ dependent GS activity, is proposed; such cation interactions may be of significance in the intracellular control of glutamine synthesis. 相似文献
5.
The G protein alpha o subunit alters morphology, growth kinetics, and phospholipid metabolism of somatic cells. 总被引:2,自引:0,他引:2 下载免费PDF全文
The physiological role of the alpha o subunit of guanine nucleotide-binding (G) protein was investigated with a murine adrenal cell line (Y1) transfected with a rat alpha o cDNA cloned in a retroviral expression vector. The parental cell line lacked detectable alpha o subunit. Expression of the alpha o cDNA in transfected cell lines was confirmed by Western blot (immunoblot) analysis. The rat alpha o subunit interacted with murine beta and gamma subunits and associated with cell membranes. Y1 cells containing large amounts of alpha o subunit had altered cellular morphology and reduced rate of cell division. In addition, GTP-gamma S-stimulated release of arachidonic acid from these cells was significantly increased compared with that in control cells. The alpha o subunit appears directly or indirectly to regulate cellular proliferation, morphology, and phospholipid metabolism. 相似文献
6.
7.
The guanine nucleotide regulatory proteins (G-proteins) which are substrates for ADP-ribosylation by pertussis toxin (alpha i-1, alpha i-2, alpha i-3 and alpha o) transduce a variety of hormonal signals. Endothelial cells express mRNA for three alpha i subtypes although the level of alpha i-1 mRNA is very low. Interleukin 1 beta (IL 1 beta), a pleiotropic inflammatory mediator which stimulates a complex series of responses in human endothelial cells leading to increased coagulation and platelet adhesion, increases expression of one subtype of alpha i (alpha i-2) mRNA in human endothelial cells as determined by Northern blot analysis without affecting the level of mRNA for other alpha-subunits. These studies show that mRNA levels for alpha i subtypes are independently regulated, suggesting that there may be subtype specificity in the cell's requirements for the Gi class of signal-transducing proteins. 相似文献
8.
9.
Mark P. Staves David P. Bloch James C. Lacey Jr. 《Origins of life and evolution of the biosphere》1988,18(1-2):97-105
Earlier studies (1) have shown there are direct correlations between the hydrophobicity ranking of most amino acids and their anticodonic nucleotides. However, four anticodonic assignments, i.e. those for Trp, Tyr, Ile and the XGA anticodons for Ser, did not correlate. It was our proposal that this failure to correlate was due to the fact that these assignments were made late, relative to the bulk of the assignments, in evolution through the mutation of existing tRNAs. We have shown (2) thatE. coli tRNAIle 1 and tRNAIle 2 were likely derived from tRNAVal 1 and tRNALys respectively andE. coli tRNATyr was possibly derived fromE. coli 5s rRNA or a common precursor with 5s rRNA (3). The fact that quite high homologies were observed in these comparisons is consistent with the late evolution of the tRNAs in question. We now examine the evolution ofE. coli tRNATrp by comparing its homology with otherE. coli tRNAs. The data suggest a possible evolutionary relationship withE. coli tRNAGly or tRNAArg. The data support the idea of the late assignment of anticodons to Trp.Deceased. 相似文献
10.
Victor N. Mikheev Dmitry S. Pavlov Daria Pakulska 《Environmental Biology of Fishes》1992,35(4):351-360
Synopsis Swimming speed and swimming path of goldfish and tetra larvae were studied in aquaria containing food patches composed of decapsulated cysts and immobilized nauplii of Artemia salina or sparsely distributed prey. The mean swimming speed of starved larvae in the medium without food was about four times higher than the speed of larvae feeding in a patch. Satiated larvae swam about 1.5 times slower than hungry fish. Consumption of single prey items by starved larvae caused the following sequence of swimming responses: handling pause (cessation of swimming), slow swimming in a restricted area, and fast swimming (approximately twice as fast as hungry larvae before encountering food) accompanied by a widening of the area searched (area increased searching). Mean swimming speed was constant over a broad range (101–103 ind·1–1 of food density, although at extreme (high or low) values of food density it depended on swimming responses of the predator. Frequency of visits to the different parts of the aquarium strongly depended on encounters of hungry fish with food particles or patches. 相似文献