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61.
EI Sinauridze RI Volkova YV Krasotkina VI Sarbash FI Ataullakhanov 《Canadian Metallurgical Quarterly》1998,1425(3):607-616
We have tested whether action potential-evoked Ca2+ influx is required to initiate clathrin-mediated synaptic vesicle endocytosis in the lamprey reticulospinal synapse. Exo- and endocytosis were temporally separated by a procedure involving tonic action potential stimulation and subsequent removal of extracellular Ca2+ (Ca2+e). A low concentration of Ca2+ ([Ca2+]e of 11 microM) was found to be required for the induction of early stages of endocytosis. However, the entire endocytic process, from the formation of clathrin-coated membrane invaginations to the generation of synaptic vesicles, proceeded in the absence of action potential-mediated Ca2+ entry. Our results indicate that the membrane of synaptic vesicles newly incorporated in the plasma membrane is a sufficient trigger of clathrin-mediated synaptic vesicle endocytosis. 相似文献
62.
BACKGROUND and aims. To compare the metabolic effects induced by the anticancer drugs, 6-mercaptopurine (6-MP), 6-thioguanine (6-TG) and 6-methylmercaptopurine riboside (MMPR), which may inhibit the de novo biosynthesis of purine nucleotides or be mis-incorporated into DNA or RNA. METHODS: Leukaemia cells were grown in culture, exposed to a thiopurine and cell extracts were analyzed for NTPs, dNTPs, drug metabolites and P-Rib-PP. RESULTS: In leukaemia cells, 6-MP was converted to MPR-MP, thio-XMP, thio-GMP, thio-GDP and thio-GTP. Metabolites of 6-TG included thio-XMP, thio-GMP, thio-GDP and thio-GTP, while MMPR-MP was the only major metabolite of MMPR, MMPR (25 microM, 4 h) induced a 16-fold increase in P-Rib-PP and 6-MP (25 microM, 4 h) induced a delayed 5.2-fold increase. MPR-MP, thio-GMP and MMPR-MP are inhibitors of amido phosphoribosyltransferase from leukaemia cells with Ki values of 114 +/- 7.10 microM, 6.20 +/- 2.10 microM and 3.09 +/- 0.30 microM, respectively. CONCLUSION: The nucleoside-5'-monophosphate derivatives of the 3 thiopurines inhibit amido phosphoribosyltransferase in growing leukaemia cells but there is also an initial inhibition of the further conversion of IMP in the pathway. In growing cells, MMPR acts solely as an inhibitor of de novo purine biosynthesis while 6-TG and to a lesser extent, 6-MP, are converted to significant concentrations of di- and tri-phosphate derivatives which may have other mechanisms of cytotoxicity. 相似文献
63.
HP Brezinschek RI Brezinschek T D?rner PE Lipsky 《Canadian Metallurgical Quarterly》1998,102(2):516-521
The variable heavy chain (V(H)) gene segment V(H)1-69/DP-10 has been shown to be over-represented in B-cell chronic lymphocytic leukaemia (CLL). Because of certain similar characteristics of their complementarity determining region 3 (CDR3), including preferential utilization of J(H)6 elements and an extended length, it has been suggested that antigenic stimulation might be involved in leukaemogenesis. Utilizing single-cell PCR to amplify and sequence genomic DNA from individual normal human peripheral blood B cells, we have obtained 7/421 productively and 1/69 nonproductively rearranged V(H) genes that used V(H)1-69/DP-10. All productive rearrangements were unmutated, used J(H)6 and had an average CDR3 length similar to that previously found in V(H)1-69/DP-10-expressing CLL cells. These results suggest that CLL may arise from B cells commonly found in the peripheral B-cell repertoire and do not represent expansion of a unique subset of specific antigen-reactive B cells. 相似文献
64.
KF Benson M Horwitz J Wolff K Friend E Thompson S White RI Richards WH Raskind TD Bird 《Canadian Metallurgical Quarterly》1998,7(11):1779-1786
Autosomal dominant familial spastic paraplegia (FSP) is a genetically heterogeneous neurodegenerative disorder displaying anticipation for which three loci have been mapped to the chromosomal positions 14q11.2-q24.3 (SPG3), 2p21-p24 (SPG4) and 15q11.1 (SPG6). The repeat expansion detection (RED) method has been used to demonstrate expanded CAG repeats in some FSP families that map to SPG4. We analyzed 20 FSP families, including four for which there is evidence for linkage to SPG4, and found that in most cases the repeat expansion detected by RED is due to non-pathogenic expansions of the chromosome 18q21.1 SEF2-1 or 17q21.3 ERDA1 locus. Polymorphic expansions at SEF2-1 and ERDA1 appear frequent and may confound RED studies in the search for genes causing disorders demonstrating anticipation. In six FSP families, however, CAG repeat expansion was detected in a subset of affected and at-risk individuals that did not result from expansion of the SEF2-1 and ERDA1 loci. Overall, 11 of 37 (30%) of the FSP patients with a CAG/CTG repeat expansion are unaccounted for by the SEF2-1 and ERDA1 loci, compared with two of 23 (9%) of the unaffected at-risk individuals and none of 19 controls. In the majority of cases these novel expansions were shorter than those previously reported. 相似文献
65.
Eui Jae RI 《Metals and Materials International》2002,8(6):591-599
Various PVD techniques have been employed with a number of bright metals like Ag, Al, Ni, and Cr. E-beam evaporated sliver films turned out to be excellent with more than 96% reflectance but the adhesion was not very good Meanwhile, the adhesion of silver films deposited by using rf magnetron sputtering showed 15 to 24Kgf/cm2. When a bias of 100 V dc was additionally applied during the magnetron processes, the film adhesions were enhanced as much as 75 to 82 Kgf/cm2, which is 5 times higher than the evaporated counterpart. Along with this, the sputter-deposited silver films have revealed reflectance values of 96% and above. Thus, it is concluded that the dc biasing during sputter-deposition can be successfully utilized to produce high quality reflective films. 相似文献
66.
Hoppe D.J. Perez R.M. Glazer S.D. 《IEEE transactions on instrumentation and measurement》1990,39(3):501-503
Temperature measurements of a high-power microwave feedhorn window during transmitter operation at 365 kW CW and 8.5 GHz made using an imaging infrared radiometer are discussed. The window under investigation was constructed of HTP-6, a high-thermal-performance material developed to shield the Shuttle Orbiter from the heat of reentry. The measurement technique is described and experimental results are presented. The window performed adequately at 365 kW CW with a center temperature of 475°C. The tests verify that HTP-6 can be used as a window material or a support structure in high-power waveguide at power densities of 1.47 kW/cm2 for extended periods of time, with no change in its mechanical characteristics 相似文献
67.
68.
69.
MD Phillips RI Grossman Y Miki L Wei DL Kolson MA van Buchem M Polansky JC McGowan JK Udupa 《Canadian Metallurgical Quarterly》1998,19(6):1055-1060
A kinetic analysis of degradation of saturated oligoguluronates by poly(alpha-L-guluronate)lyase from Corynebacterium sp. ALY-1 strain was done. The saturated oligoguluronates were prepared by hydrolyzing poly alpha-1,4-L-guluronate from alginate with HCl, and then by gel filtration on a Bio-Gel P-6 column. The saturated pentaguluronate or above were rapidly degraded by the enzyme, while tetraguluronate was slowly degraded. From the dependency of the catalytic rate constant (kcat) on the degree of polymerization of substrates, the enzyme was found to have a subsite size corresponding to hexaguluronate units. The action pattern of the enzyme on hexaguluronate suggested that the catalytic site of the enzyme was matched to the linkage between the second and third uronic residue from the non-reducing end, since the substrate was mainly split into a unsaturated tetramer and a saturated dimer from a HPLC analysis. 相似文献
70.
We report a patient with biopsy-proven progressive multifocal leukoencephalopathy (PML) who was serially imaged with MRI and magnetization transfer imaging. The magnetization transfer ratio (MTR) was profoundly and significantly diminished when compared with normal control subjects. The pattern of MTR was distinct from that of MS and periventricular ischemic white matter disease. Magnetization transfer imaging techniques may aid in the differential diagnosis of PML. 相似文献