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1.
Abstract— An analysis of the [3 H]DFP-labelled catalytic subunits of mammalian (bovine SCG) acetylcholinesterase (AChE, EC 3.1.1.7.) indicates a monomer molecular weight of 75,000. This is equivalent to the mass previously determined for the smallest active form and demonstrates that the globular, or G forms, are respectively monomeric (G1 form, 4S), dimeric (G2 form, 6.5S) and tetrameric (G4 form, 10S). In the tetrameric G4 form the catalytic chains are associated in dimers, by disulphide bonds.
The effect of reduction and proteolysis has shown that the dimeric form (G2 form, 6.5S) is readily reduced into G1 , while the tetramer G4 is very stable, being only dissociated by a combination of reduction and proteolysis by high concentration of trypsin. The asymmetric forms A12 (16S), A8 (13S) and A4 (9S) are not sensitive to reduction, but are readily dissociated by low concentrations of trypsin, into each other, progressively liberating isolated tetramers. We obtained essentially identical results with AChE preparations from rat brain or superior cervical ganglion. These observations support a general model for the quaternary structure of acetylcholinesterase molecular forms. 相似文献
The effect of reduction and proteolysis has shown that the dimeric form (G
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Actinomycin D (0.5 μg/ml) did not prevent M stage cells from entering G1 stage, but blocked their progress from G1 to S stage. The position of the block was approximately 1.4 hr before S stage or just after the beginning of G1 stage. Actinomycin D in this concentration also significantly depressed uridine-3 H uptake into G1 stage cells, but did not suppress leucine-3 H uptake by M and G1 cells. This suggests that some proteins may be synthesized in M and G1 stage cells by messenger RNA left over from the previous cell cycle. However, entry of G1 cells into S stage would require synthesis of new messenger RNA near the beginning of G1 stage. Puromycin (10 μg/ml) did not prevent M cells from entering G1 stage, but blocked their progress from G1 to S stage. The site of blockage was about 0.7 hr before S stage or in the first two-third of G1 stage. This might be the site where the cells synthesize new G1 proteins necessary for entry to S stage.
Comparison of sensitivities of G1 and G2 stages to the two antibiotics reveals that the puromycin sensitivity of G1 cells was similar to that of G2 cells, but the actinomycin D sensitivity of G1 was greater than that of G2 cells. 相似文献
Comparison of sensitivities of G
4.
Abstract. Multivariate analysis of the expression of cyclin proteins and DNA content has opened new possibilities for the study of the cell cycle. By virtue of their cell cycle phase specificity, the expression of cyclins may serve, in addition to DNA content, as another marker of a cell's position in the cycle, and provide information about the proliferative potential of cell populations. Several applications of the methodology based on bivariate analysis of DNA content v . expression of B, E and D type cyclins are reviewed: 1 expression of cyclins by individual cells during their progression through the cycle can be studied, using exponentially growing cells without the necessity of cell synchronization or other perturbations of the cycle; 2 cells having the same DNA content but residing in different phases of the cycle (e.g. G2 diploid v. G1 tetraploid) can be distinguished; 3 cell transition from G0 to G1 and progression through G1 (e.g. mitogen stimulated lymphocytes) can be assayed; 4 the population of proliferating cells can be distinguished from noncycling cells based on dual cell labelling with a G1 and G2 cyclin antibody; 5 cyclin restriction points can serve as additional cell cycle landmarks to map the point of action of antitumour drugs; 6 unscheduled expression of cyclins (e.g. the presence of cyclin B1 during G1 and S) can be detected in several tumour transformed cell lines, possibly indicating disregulation of the machmery of cell cycle progression. The last finding 6 is of special importance, because such disregulation may be of prognostic consequence in human tumours. 相似文献
5.
The G2 block is a major response of cells to DNA damage and seem to be induced independently of p53 status. It is thought that the G2 block has a protective function and allows cells to repair their DNA. The molecular events involved in the formation of the G2 block therefore are of great interest. We have used pentoxifylline, a potent G2 delay abrogator, to study the expression of an essential component of the mitosis promoting complex (MPF), cyclin B1. Cyclin B1/G2 ratios are used to show that irradiation induces a decrease in cyclin B1 expression and that pentoxifylline restores cyclin B1 expression to control level. This confirms that suppression of cyclin B1 plays a role in the formation of the G2 cell cycle delay, and that elevating cyclin B1 expression is part of the mechanism of action of pentoxifylline on G2 blocked cells. 相似文献
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7.
F. Zhang J. J. Godyn M. Uskokovic L. Binderup G. P. Studzinski 《Cell proliferation》1994,27(11):643-654
Abstract. Differentiation of mammalian cells is accompanied by reduced rates of proliferation and an exit from the cell cycle. Human leukemic cells HL60 present a widely used model of neoplastic cell differentiation, and acquire the monocytic phenotype when exposed to analogs of vitamin D3 (VD3 ). The maturation process is accompanied by two blocks in the cell cycle: an arrest in the G1 /G0 phase, and a recently described G2 + M block. In this study we have analyzed the traverse of the cell cycle phases of the well-differentiating HL60-G cells exposed to one of ten analogs of VD3 , and compared the cell cycle effects of each compound with its potency as a differentiation-inducing agent. We found that in general there was a good correlation between the effects of these compounds on the cell cycle and on differentiation, but the best cell cycle predictor of differentiation potency was the extent of accumulation of the cells in the G2 compartment. All analogs induced a marked decrease in the mitotic index, and polynucleation of HL60 cells was produced, especially by compounds which were effective as inducers of differentiation. Time course studies showed that induction of differentiation was accompanied by a transient increase of the proportion of cells in the G2 + M compartment, but preceded the G1 to S, and the G2 compartment blocks. These studies indicate that complex changes in the cell cycle traverse accompany, but do not precede, the acquisition of the monocytic phenotype by HL60 cells. 相似文献
8.
Abstract. We have previously found that DNA replication was affected within one cell cycle after seeding Chinese hamster ovary (CHO) cells in the presence of the polyamine biosynthesis inhibitor 2-difluoromethylornithine (DFMO). We could, however, not rule out if this was due to an effect on the G1 /S transition and/or on DNA synthesis elongation. In the present paper, we use a bromodeoxyuridine-flow cytometric method to more specifically study the G1 /S transition, the S phase length, and the progression of cells from S phase through G2 + M and into G1 , after seeding plateau phase CHO cells at low density in the absence or presence of 5 mM DFMO. We report here that DFMO-induced polyamine depletion increased the length of the S phase within one cell cycle after seeding of CHO cells in the presence of the inhibitor. No effect on the G1 /S transition was observed until 2 days after seeding, suggesting that a DFMO-induced lengthening of the G1 phase occurred later than the effect on S phase progression. These results imply that the G2 + M phase was not prolonged until 2 days after seeding CHO cells in the presence of DFMO. 相似文献
9.
Abstract— Gangliosides were isolated from myelin prepared from mouse brains of different ages (23 to 490 days). Quantitative estimation of lipid-bound sialic acid levels indicated a gradual increase from 560 μg/g of myelin at 23 days to about 1200 μg/g of myelin at older ages. The major ganglioside in all myelin preparations was the monosialoganglioside G4 (GM1 ). However, considerable amounts of di- and trisialo species also were found in myelin from young animals. In contrast to human myelin in which the monosialoganglioside, sialosylgalactosylceramide (G7 ) was highly enriched (L edeen et al. , 1973), a much smaller enrichment of this ganglioside was noticed in mouse brain myelin. Ganglioside G7 was not detectable in myelin until the animals were 35 days old, and showed a slight increase with increasing age after that. The results strongly indicated that the concentration of G7 in myelin is species specific and age dependent. The study also demonstrated that the ganglioside accretion in developing mouse brain myelin was attributable to the enrichment of monosialogangliosides G4 (GM1 ), G5 (GM2 ) and G7 at the expense of polysialogangliosides. 相似文献
10.
Juan Cabezas-Herrera María Teresa Moral-Naranjo F. Javier Campoy Cecilio J. Vidal 《Journal of neurochemistry》1997,69(5):1964-1974
Abstract: The distribution and glycosylation of acetylcholinesterase (AChE) forms in vesicles derived from sarcoplasmic reticulum of normal muscle (NMV) were investigated and compared with those from dystrophic muscle vesicles (DMV). AChE activity was similar in NMV and DMV. Most of the AChE in NMV and half in DMV were released with Triton X-100. Asymmetric (A12 ) and globular hydrophilic and amphiphilic (GH 4 , GA 4 , GA 2 , and GA 1 ) AChE species occurred in NMV and DMV, the lighter forms being predominant. The percentage of GH 4 and GA 4 decreased in DMV. A fraction of the AChE that could not be extracted with detergent was detached with collagenase. Most of the detergent-released A12 AChE from NMV and nearly half in DMV failed to bind to Ricinus communis agglutinin (RCA-I). Conversely, the collagenase-detached isoforms bound to RCA, revealing that asymmetric AChE associated with internal membranes or basal lamina differed in glycosylation. Moreover, nearly half of GA 4 AChE in DMV and a few in NMV bound to RCA. Most of the RCA-unreactive GA 4 forms in NMV come from sarcolemma. The results indicate that dystrophy induces minor changes in the distribution and glycosylation of AChE forms in internal membranes of muscle. 相似文献
11.
Abstract. The physiologically active form of vitamin D3 , 1,25-dihydroxy-vitamin D3 , (1,25(OH)2 , D3 ), induces differentiation of several types of myeloid leukaemia cells. The acquisition of monocyte-like phenotype is accompanied by slower progression through the cell cycle, and G1 , block has been reported to be the basis of this effect. It is shown here that human promyelocytic leukaemia HL60 cells treated with analogues of vitamin D3 , which are potent inducers of monocytic differentiation, have an additional cell cycle block. Exposure to 10-7 m 1,25(OH)2 , D3 , or 1,25-(OH)2 ,-16-ene-D3 resulted in monocytic differentiation and the expected G1 , block evident at approximately 48 h in a rapidly differentiating variant of HL60 cells (HL60-G), and at 96 h in the more slowly differentiating HL60-240 cells. In addition, a G2 ,+M block was noted at approximately 72 h in HL60-G and HL60-240 cells. Exposure to vitamin D3 , analogues also markedly increased the number of dikaryons, suggesting that cytokinesis was impaired more than karyokinesis. Treatment with a third analogue 25-hydroxy-16,23-diene-D3 , produced little differentiation and had minimal effects on the cell cycle parameters. These findings indicate that vitamin D3 , analogues regulate cell proliferation by control of the transition of G1 , and G2 ,+M phases, reminiscent of the cdc2/CDK2 type of cell cycle control. 相似文献
12.
Experiments in mice on the fraction of haemopoietic stem cells in S-phase after irradiation indicated that a large fraction of the cells resting in G0 will enter S-phase after a very short interval of time.
After excluding alternative explanations it must be concluded that cells in G0 have completed all preparations for going into S-phase or, in other words, that the localization of these G0 cells in relation to other phases of the cell cycle must be between G1 and S-phase. 相似文献
After excluding alternative explanations it must be concluded that cells in G
13.
Abstract— Gangliosides were isolated from plaque tissue and normal appearing white matter of multiple sclerosis (MS) brain. All four plaques showed decreased ganglioside concn relative to normal human white matter on a wet wt basis, but significant elevation in terms of dry wt. The wet wt and dry wt concn of MS white matter gangliosides showed smaller but statistically significant decreases below normal. Thin-layer patterns of the plaques showed several departures from normal white matter, including decrease of G4 and G5 , and complete loss of G7 (sialosylgalactosylceramide). Most of the plaques had significant elevation of G2A and G3A along with increases of the slower-migrating polysialogangliosides. An additional ganglioside was present between G2 and G2A which was not seen in normal white matter. The TLC pattern of MS white matter gangliosides was essentially normal. The evidence for a general decrease of acidic lipids within normal appearing white matter is discussed. 相似文献
14.
Naoto Ohnishi Hiroaki Kodania Satoshi Ando Atsushi Komamine 《Physiologia plantarum》1990,80(1):95-101
The effects of inhibition of the synthesis of protein, mRNA or rRNA on the progression of the cell cycle have been analyzed in cultures of Catharanthus roseus in which cells were induced to divide in synchrony by the double phosphate starvation method. The partial inhibition of protein synthesis at the G1 phase by anisoniycio or cycloheximide caused the arrest of cells in the G1 phase or delayed the entry of cells into the S phase. When protein synthesis was partially inhibited at the S phase, cell division occurred to about the same extent as in the control. When asynchronously dividing cells were treated with cycloheximide, cells accumulated in the G1 phase, as shown by flow-cytometric analysis. The partial inhibition of mRNA synthesis by α-amanitin at the G1 phase caused the arrest of cells in the G1 phase, although partial inhibition of mRNA synthesis at the S phase had little effect on cell division. In the case of inhibition of synthesis of rRNA by actinomycin D at the G1 phase, initiation of DNA synthesis was observed, but no subsequent DNA synthesis or the division of cells occurred. However, the addition of actinomycin D during the S phase had no effect on cell division. These results suggest that specific protein(s), required for the progression of the cell cycle, are synthesized in the G1 phase, and that the mRNA(s) that encode these proteins are also synthesized at the G1 phase. 相似文献
15.
N 5 N 10 -Methylenetetrahydromethanopterin reductase was purified 13-fold to apparent homogeneity from methanol grown Methanosarcina barkeri . The colourless enzyme was found to be composed of four identical subunits of apparent molecular mass 36 kDa. It catalysed the reduction of methylenetetrahydromethanopterin ( K m =15 μM) to methyltetrahydromethanopterin with reduced coenzyme F420 ( K m =12 μM) at a specific rate ( V max ) of 2200 μmol min−1 · mg protein−1 ( K cat =1320 s−1 ). With respect to coenzyme specificity, molecular properties and catalytic mechanism the enzyme was found to be similar to CH2 =H4 MPT reductase of Methanobacterium thermoautotrophicum which phylogenetically is only distantly related to M. barkeri . 相似文献
16.
Abstract. Chinese hamster ovary cells were arrested in the G2 phase of the cell cycle by X-irradiation. When subsequently treated with 5 mM caffeine the arrested population progressed into mitosis as a synchronous cohort where it was harvested by mitotic cell selection. This procedure provides a means to isolate cell populations treated in G2 , for the investigation of G2 arrest. Comparisons were made of the number of cells retrieved from G2 arrest with the number suffering arrest, as determined by flow cytometry and by matrix algebraic simulations of irradiated cell progression. the retrieved population was not significantly less than expected for doses up to 3.5 Gy, indicating that the retrieval process does not favour the isolation of any population subset below this dose. Cell populations retrieved from arrest at varying intervals (0-3 h) after irradiation (0-3.5 Gy) showed an increase in survival with increase in interval, consistent with repair of potentially lethal damage. the repair curves (surviving fraction us time) were each described by a single exponential. G2 cells that were brought to mitosis without a period of arrest exhibited the same radiation response as cells irradiated in mitosis. 相似文献
17.
Kanji Takeo Reiko Tanaka Makoto Miyaji Kazuko Nishimura 《FEMS microbiology letters》1995,129(2-3):231-235
Abstract Stationary-phase cells of Cryptococcus neoformans displayed two morphological characteristics: virtually all the cells were unbudded even in the early stationary phase and even when grown in rich media, and average cell size increased from that of exponential-phase cells. DNA contents for small and large stationary-phase cells were determined by quantitative fluorescence microscopy after DNA staining with propidium iodide or DAPI. Small cells contained G, DNA, whereas large unbudded cells had either a G2 or G1 DNA content, indicating that Cr. neoformans can enter into the stationary phase from either the G1 or G2 period. 相似文献
18.
Influence of denervation on the regeneration of Pleurodele limbs 总被引:2,自引:0,他引:2
Mustapha Oudkhir Bénoni Boilly Emile Lheureux Bernard Lassalle 《Differentiation; research in biological diversity》1985,29(2):116-120
Abstract. A cytophotometric study of Feulgen-stained mesenchymal cell nuclei from regeneration blastemas of both innervated and denervated limbs over the 1st 7 days following the midbud stage showed a diminution of the percentage of cells in the S + G2 phases and a corresponding augmentation of the percentage of cells in the G0 + G1 phases. This change, which was temporally correlated with the redifferentiation of the innervated blastemas, was greater in denervated blastemas, even though they do not redifferentiate. From these results, it is concluded that the denervation of midbud blastemas brings about either an extension of the G1 phase or an exiting from the cell cycle to G1 (G0–1 ), or both phenomena. 相似文献
19.
Pertussis Toxin-Insensitive Signaling of the ORL1 Receptor: Coupling to Gz and G16 Proteins 总被引:1,自引:1,他引:0
Joy S. C. Chan Lisa Y. Yung Jonathan W. M. Lee Ya-Lan Wu Gang Pei Yung H. Wong 《Journal of neurochemistry》1998,71(5):2203-2210
Abstract: Nociceptin/OFQ is the endogenous ligand for the G protein-coupled opioid receptor-like (ORL1 ) receptor. To elucidate the cellular functions of the ORL1 receptor, we examined its ability to interact with Gz and G16 , two pertussis toxin (PTX)-insensitive G proteins that are known molecular partners for the opioid receptors. In HEK 293 cells transiently expressing the ORL1 and dopamine D1 receptors, nociceptin/OFQ dose-dependently inhibited dopamine-stimulated cyclic AMP (cAMP) accumulation in a PTX-sensitive manner. However, PTX failed to block the nociceptin/OFQ-induced inhibition of dopamine-stimulated cAMP accumulation in HEK 293 cells co-expressing the α-subunit of Gz . This result indicates functional interaction between the ORL1 receptor and Gz . A similar result was obtained with retinoic acid-differentiated SH-SY5Y cells, which endogenously express both the ORL1 receptor and Gz . When the ORL1 receptor was transiently co-expressed in COS-7 cells with the α-subunit of G16 , nociceptin/OFQ dose-dependently stimulated the formation of inositol phosphates. Nociceptin-induced stimulation of phospholipase C was absolutely dependent on the co-expression of α16 and exhibited the appropriate ligand selectivity. In terms of its ability to interact with PTX-insensitive G proteins, the ORL1 receptor behaves very much like the opioid receptors. 相似文献
20.
Jonathan W. M. Lee Sushma Joshi Joy S. C. Chan Yung H. Wong 《Journal of neurochemistry》1998,70(5):2203-2211
Abstract: The μ-opioid receptor has recently been shown to stimulate phosphoinositide-specific phospholipase C via the pertussis toxin-sensitive G16 protein. Given the promiscuous nature of G16 and the high degree of resemblance of signaling properties of the three opioid receptors, both δ- and κ-opioid receptors are likely to activate G16 . Interactions of δ- and κ-opioid receptors with G16 were examined by coexpressing the opioid receptors and Gα16 in COS-7 cells. The δ-selective agonist [ d -Pen2 , d -Pen5 ]enkephalin potently stimulated the formation of inositol phosphates in cells coexpressing the δ-opioid receptor and Gα16 . The δ-opioid receptor-mediated stimulation of phospholipase C was absolutely dependent on the coexpression of simeter for quality control of blood units and irradiators. 13. Transfusion 1993 ; 33 : 898 – 901 . [PubMed link] 14. Butson MJ , Yu PK , Cheung T , et al . Dosimetry of blood irradiation with radiochromic film. Transfus Med 1999 ; 9 : 205 – 8 . [PubMed link] 15. Nath R , Biggs PJ , Ling CC , et al . AAPM code of practice for radiotherapy accelerators: Report of AAPM Radiation Therapy Task Group No. 45. Med Phys 相似文献