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71.
Synthesis of histone H4 by mouse oocytes and unfertilized eggs has been examined by using a modified high-resolution two-dimensional gel electrophoresis procedure capable of resolving basic proteins (M. J. LaMarca and P. M. Wassarman, 1979, Develop. Biol.73, 103–119). Histones were separated on such gels and observed rates of incorporation of [35S]methionine into histone H4 were converted into absolute rates of synthesis by using previously determined values for the absolute rates of total protein synthesis in mouse oocytes and unfertilized eggs Schultz et al., 1979a, Schultz et al., 1979b. Histone H4 was synthesized at all stages of oogenesis examined, and accounted for 0.07, 0.05, and 0.04% of total protein synthesis in growing oocytes, fully grown oocytes, and unfertilized eggs, respectively. During oocyte maturation the absolute rate of histone H4 synthesis decreased by about 40%, as compared to a 23% decrease in the rate of total protein synthesis during the same period. These measurements indicate that enough histone is synthesized during oogenesis in the mouse to support two to three cell divisions. Examination of the intracellular location of newly synthesized proteins in fully grown oocytes revealed that histone H4 was highly concentrated in the nucleus (germinal vesicle), whereas total protein and tubulin were not. Nearly 50% of the histone H4 synthesized during a 5-hr period was located in the oocyte's germinal vesicle, as compared to 1.9 and 0.9% for total protein and tubulin, respectively. These results are compared with those obtained using oocytes and eggs from nonmammalian animal species. 相似文献
72.
73.
Terry A. Potter Suzanne M. Watt Antony W. Burgess Ian F. C. McKenzie 《Immunogenetics》1979,8(1):461-473
Serological analysis of highly purified (>97%) mouse peritoneal exudate neutrophils using a protein-A rosetting technique, showed that these cells possessed the surface phenotype: Ig–, Thy-1–, Ly-1–, Ly-2–, Ly-3–, Ly-4+, Ly-5+, Ly-6+, Ly-7–, Ia–, FcR+ and C3R+. 相似文献
74.
Flash-induced absorption changes of Triton-solubilized Photosystem I particles from spinach were studied under reducing and/or illumination conditions that serve to alter the state of bound electron acceptors. By monitoring the decay of P-700 following each of a train of flashes, we found that P-430 or components resembling it can hold 2 equivalents of electrons transferred upon successive illuminations. This requires the presence of a good electron donor, reduced phenazine methosulfate or neutral red, otherwise the back reaction of P-700+ with P-430 occurs in about 30 ms. If the two P-430 sites, designated Centers A and B, are first reduced by preilluminating flashes or chemically by dithionite under anaerobic conditions, then subsequent laser flashes generate a 250 μs back reaction of P-700+, which we associate with a more primary electron acceptor A2. In turn, when A2 is reduced by background (continuous) illumination in presence of neutral red and under strongly reducing conditions, laser flashes then produce a much faster (3 μs) back reaction at wavelengths characteristic of P-700. We associate this with another more primary electron acceptor, A1, which functions very close to P-700. The organization of these components probably corresponds to the sequence . The relation of the optical components to acceptor species detected by EPR, by electron-spin polarization or in terms of peptide components of Photosystem I is discussed.Preliminary experiments with broken chloroplasts suggest that an analogous situation occurs there, as well. 相似文献
75.
Cell surface changes occurring before and during gastrulation in Xenopus laevis embryos have been examined by scanning electron microscopy (SEM). Our study covers the period of development from very young blastulae (stage 7) to late gastrulae (stage . Before the onset of the epibolic movement there is evidence of locomotory activity of the cells lining the blastocoel at the animal pole. In the medim- (stage 8) and small-cell (stage 9) blastula, when pregastrulation movements are progressing rapidly, microvilli appear in the interstices between cells, both at the animal and at the vegetal pole. In the gastrula, most of the cells close to the blastopore have either their entire exposed surface or part of it covered with microvilli. On the other hand, the cells that have just reached the blastopore and have become clubshaped do not display microvilli on their surfaces; microvilli are also absent on the surface of the cells that have undergone invagination. The invaginated chorda-mesoderm is made up of single fibroblastlike cells with long thin filopodia which are interwoven with those of nearby cells. The observations are discussed in relation to changes in cell-to-cell connections and to the role of cell surface organization in the morphogenetic movements of gastrulation. 相似文献
76.
Vicky P. Chen Heidi Q. Xie Wallace K. B. Chan K. Wing Leung Gallant K. L. Chan Roy C. Y. Choi Suzanne Bon Jean Massoulié Karl W. K. Tsim 《The Journal of biological chemistry》2010,285(35):27265-27278
Acetylcholinesterase (AChE) is anchored onto cell membranes by the transmembrane protein PRiMA (proline-rich membrane anchor) as a tetrameric globular form that is prominently expressed in vertebrate brain. In parallel, the PRiMA-linked tetrameric butyrylcholinesterase (BChE) is also found in the brain. A single type of AChE-BChE hybrid tetramer was formed in cell cultures by co-transfection of cDNAs encoding AChET and BChET with proline-rich attachment domain-containing proteins, PRiMA I, PRiMA II, or a fragment of ColQ having a C-terminal GPI addition signal (QN-GPI). Using AChE and BChE mutants, we showed that AChE-BChE hybrids linked with PRiMA or QN-GPI always consist of AChET and BChET homodimers. The dimer formation of AChET and BChET depends on the catalytic domains, and the assembly of tetramers with a proline-rich attachment domain-containing protein requires the presence of C-terminal “t-peptides” in cholinesterase subunits. Our results indicate that PRiMA- or ColQ-linked cholinesterase tetramers are assembled from AChET or BChET homodimers. Moreover, the PRiMA-linked AChE-BChE hybrids occur naturally in chicken brain, and their expression increases during development, suggesting that they might play a role in cholinergic neurotransmission. 相似文献
77.
W Palm JL Sampaio M Brankatschk M Carvalho A Mahmoud A Shevchenko S Eaton 《PLoS genetics》2012,8(7):e1002828
Interorgan lipid transport occurs via lipoproteins, and altered lipoprotein levels correlate with metabolic disease. However, precisely how lipoproteins affect tissue lipid composition has not been comprehensively analyzed. Here, we identify the major lipoproteins of Drosophila melanogaster and use genetics and mass spectrometry to study their assembly, interorgan trafficking, and influence on tissue lipids. The apoB-family lipoprotein Lipophorin (Lpp) is the major hemolymph lipid carrier. It is produced as a phospholipid-rich particle by the fat body, and its secretion requires Microsomal Triglyceride Transfer Protein (MTP). Lpp acquires sterols and most diacylglycerol (DAG) at the gut via Lipid Transfer Particle (LTP), another fat body-derived apoB-family lipoprotein. The gut, like the fat body, is a lipogenic organ, incorporating both de novo-synthesized and dietary fatty acids into DAG for export. We identify distinct requirements for LTP and Lpp-dependent lipid mobilization in contributing to the neutral and polar lipid composition of the brain and wing imaginal disc. These studies define major routes of interorgan lipid transport in Drosophila and uncover surprising tissue-specific differences in lipoprotein lipid utilization. 相似文献
78.
The reaction of the title complex with DNA has been examined. Addition of [(bpy)2(OH2)RuORu(OH2) (bpy)2]4+ to DNA leads to the reduction of the complex to Ru(bpy)2(OH2)22+, as indicated by absorption spectroscopy and cyclic voltammetry. The reaction is accelerated by Mg2+. The combined evidence points to a mechanism where the oxo-bridged dimer is hydrolyzed to a monomeric Ru(III) complex that is capable of oxidizing DNA to effect strand scission. Gel electrophoresis demonstrates nicking of supercoiled /gfX174 DNA by [(bpy)2(OH2)RuORu(OH2) (bpy)2]4+, and double-stranded cleavage is observed in the presence of Mg2+. Linearization of the plasmid prior to treatment with the complex does not lead to further fragmentation, suggesting that supercoiling is required to realize double-stranded cleavage. 相似文献
79.
80.
NARC-1/PCSK9 and its natural mutants: zymogen cleavage and effects on the low density lipoprotein (LDL) receptor and LDL cholesterol 总被引:1,自引:0,他引:1
Benjannet S Rhainds D Essalmani R Mayne J Wickham L Jin W Asselin MC Hamelin J Varret M Allard D Trillard M Abifadel M Tebon A Attie AD Rader DJ Boileau C Brissette L Chrétien M Prat A Seidah NG 《The Journal of biological chemistry》2004,279(47):48865-48875
The discovery of autosomal dominant hypercholesterolemic patients with mutations in the PCSK9 gene, encoding the proprotein convertase NARC-1, resulting in the missense mutations suggested a role in low density lipoprotein (LDL) metabolism. We show that the endoplasmic reticulum-localized proNARC-1 to NARC-1 zymogen conversion is Ca2+-independent and that within the zymogen autocatalytic processing site SSVFAQ [downward arrow]SIP Val at P4 and Pro at P3' are critical. The S127R and D374Y mutations result in approximately 50-60% and > or =98% decrease in zymogen processing, respectively. In contrast, the double [D374Y + N157K], F216L, and R218S natural mutants resulted in normal zymogen processing. The cell surface LDL receptor (LDLR) levels are reduced by 35% in lymphoblasts of S127R patients. The LDLR levels are also reduced in stable HepG2 cells overexpressing NARC-1 or its natural mutant S127R, and this reduction is abrogated in the presence of 5 mm ammonium chloride, suggesting that overexpression of NARC-1 increases the turnover rate of the LDLR. Adenoviral expression of wild type human NARC-1 in mice resulted in a maximal approximately 9-fold increase in circulating LDL cholesterol, while in LDLR-/- mice a delayed approximately 2-fold increase in LDL cholesterol was observed. In conclusion, NARC-1 seems to affect both the level of LDLR and that of circulating apoB-containing lipoproteins in an LDLR-dependent and -independent fashion. 相似文献