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1.
The molybdenum and tungsten dinitrogen-organonitrile complexes trans-[M(N2)(NCR)(dppe)2] (2, M=Mo; 4, M=W; R=Ph, C6H4Me-p, C6H4OMe-p, Me; dppe=Ph2PCH2CH2PPh2) underwent double protonation at the nitrile carbon atom with loss of N2 and a change in oxidation state to +4 on treatment with hydrochloric acid to afford the cationic imido complexes trans-[MCl(NCH2R)(dppe)2]+. The solid-state structure of trans-[WCl(NCH2CH3)(dppe)2][PF6]·CH2Cl2 was determined by single-crystal X-ray analysis. Protonation of complexes 2 by fluoroboric acid or hydrobromic acid also formed the similar imido complexes trans-[MoX(NCH2R)(dppe)2]+ (X=F, Br). In contrast, the dinitrogen complex trans-[Mo(N2)2(dppe)2] reacted with two equiv. of benzoylacetonitrile, a nitrile with acidic CH hydrogen atoms, to give the nitrido complex trans-[Mo(N)(NKCCHCOPh)(dppe)2] (12), which was accompanied by evolution of dinitrogen and the formation of 1-phenyl-2-propen-1-one in high yields. For complex 12, the zwitterionic structure, where the anionic enolate ligand PhC(O+)=CHCN coordinates to the cationic Mo(IV) center through its nitrogen atom, was confirmed by spectroscopic measurements and single-crystal X-ray analysis. A unique intermolecular aromatic C---HO hydrogen bonding was observed in that crystal structure. Complex 12 is considered to be formed via the cleavage of the CN triple bond of benzoylacetonitrile on the metal. A reaction mechanism is proposed, which includes the double protonation of the nitrile carbon atom of the ligating benzoylacetonitrile on a low-valent molybdenum center. 相似文献
2.
Hiroyuki Kozu Isao Kobayashi Mitsutoshi Nakajima Kunihiko Uemura Seigo Sato Sosaku Ichikawa 《Food biophysics》2010,5(4):330-336
This paper uses computational fluid dynamics to simulate and analyze intragastric fluid motions induced by human peristalsis.
We created a two-dimensional computational domain of the distal stomach where peristalsis occurs. The motion of the gastric
walls induced by an antral contraction wave (ACW) on the wall of the computational domain was well simulated using a function
defined in this study. Retropulsive flow caused by ACW was observed near the occluded region, reaching its highest velocity
of approximately 12 mm/s in the narrowest region. The viscosity of the model gastric contents applied in this study hardly
affected the highest velocity, but greatly affected the velocity profile in the computational domain. The shear rate due to
gastric fluid motion was calculated using the numerical output data. The shear rate reached relatively high values of approximately
20 s−1 in the most occluded region. The shear rate profile was almost independent of the fluid viscosity. We also simulated mass
transfer of a gastric digestive enzyme (pepsin) in model gastric content when peristalsis occurs on the gastric walls. The
visualized simulation results suggest that gastric peristalsis is capable of efficiently mixing pepsin secreted from the gastric
walls with an intragastric fluid. 相似文献
3.
Cloning and sequencing of Schizosaccharomyces pombe DNA topoisomerase I gene, and effect of gene disruption. 总被引:18,自引:7,他引:11
We cloned the structural gene topl+ for Schizosaccharomyces pombe DNA topoisomerase I (topo I) by hybridization. An eight-fold increase of topo I relaxing activity was obtained in S. pombe cells transformed with multicopy plasmid with topl+ insert. Nucleotide sequence determination showed a hypothetical coding frame interrupted by two short introns, encoding a 812 residue polypeptide (M.W. 94,000), 43 residues longer than and 47% homologous to Saccharomyces cerevisiae topo I. We show that the topl (null) strain made by gene disruption is viable, although its generation time is 20% longer than that of wild type. The topl locus is mapped in the long arm of chromosome II, using the Leu+ marker integrated with the cloned topl+ sequence. We constructed a double mutant topl (null) top2 (ts) and found its defective phenotype similar to that of previously obtained topl (heat sensitive) top2 (ts). The other double mutant topl (null) top2 (cs), however, was lethal. Our results suggest that topl+ gene of S. pombe is dispensable only if topo II activity is abundant. 相似文献
4.
numb, a gene required in determination of cell fate during sensory organ formation in Drosophila embryos 总被引:8,自引:0,他引:8
Neurons and support cells of each sensory organ in Drosophila embryos are most likely derived from a single precursor cell. This cell lineage is affected in numb mutants. Morphological alterations of sensory structures, as well as changes in the number of cells expressing cell type-specific markers, indicate that sensory neurons in numb mutant embryos are transformed into lineage-related nonneuronal support cells. Thus the numb gene controls the fate of progeny derived from sensory organ precursors. The numb gene has been isolated by the plasmid rescue method. The structure of its predicted product is discussed. 相似文献
5.
6.
By incubating platelets at low temperature (10 degrees C), the relationship between Ca2+ mobilization and formation of inositol 1,4,5-trisphosphate (IP3) in thrombin stimulated platelets could be precisely investigated. In the presence of 1 mM EGTA, time dependent changes in the intracellular free calcium concentration [( Ca2+]i) were closely related to those in IP3 formation. Time course of the influx of external Ca2+, estimated by delta [Ca2+]i obtained by subtracting [Ca2+]i in the presence of 1 mM EGTA from that in the presence of 1 mM CaCl2 was also very similar to that of IP3 formed. Furthermore, the increase in delta [Ca2+]i was extremely well correlated with the amount of IP3 formed (Y = 49X - 34, r = 0.99). Thus, these data indicate that IP3 might be involved not only in intracellular Ca2+ mobilization but in Ca2+ influx of human platelets stimulated by thrombin. 相似文献
7.
Calyculin A and okadaic acid: inhibitors of protein phosphatase activity 总被引:44,自引:0,他引:44
H Ishihara B L Martin D L Brautigan H Karaki H Ozaki Y Kato N Fusetani S Watabe K Hashimoto D Uemura 《Biochemical and biophysical research communications》1989,159(3):871-877
Calyculin A and okadaic acid induce contraction in smooth muscle fibers. Okadaic acid is an inhibitor of phosphatase activity and the aims of this study were to determine if calyculin A also inhibits phosphatase and to screen effects of both compounds on various phosphatases. Neither compound inhibited acid or alkaline phosphatases, nor the phosphotyrosine protein phosphatase. Both compounds were potent inhibitors of the catalytic subunit of type-2A phosphatase, with IC50 values of 0.5 to 1 nM. With the catalytic subunit of protein phosphatase type-1, calyculin A was a more effective inhibitor than okadaic acid, IC50 values for calyculin A were about 2 nM and for okadaic acid between 60 and 500 nM. The endogenous phosphatase of smooth muscle myosin B was inhibited by both compounds with IC50 values of 0.3 to 0.7 nM and 15 to 70 nM, for calyculin A and okadaic acid, respectively. The partially purified catalytic subunit from myosin B had IC50 values of 0.7 and 200 nM for calyculin A and okadaic acid, respectively. The pattern of inhibition for the phosphatase in myosin B therefore is similar to that of the type-1 enzyme. 相似文献
8.
Site-directed mutagenesis to fine-tune enzyme specificity 总被引:1,自引:0,他引:1
We have used a combination of a genetic selection and oligonucleotide-directed mutagenesis to introduce a series of amino acid replacements for a single residue into Escherichia coli glutaminyl-tRNA synthetase. The mutant enzymes mischarge supF tRNA(Tyr), with glutamine, to varying degrees depending on the polarity of the side chain introduced but apparently not depending on the size or shape of the side chain. These results indicate that repulsive charge-charge interactions may be important for specific recognition of nucleic acids by proteins and illustrate how a mutant, derived from genetic selection, may be further modified in activity by oligonucleotide-directed mutagenesis. 相似文献
9.
The protein factor which binds to the upstream activating sequence of Saccharomyces cerevisiae ENO1 gene. 总被引:11,自引:2,他引:9 下载免费PDF全文
Using a gel retardation assay it was shown that the 87 bp DNA fragment (UAS87) containing the upstream activating sequence (UAS) of S. cerevisiae EN01 gene and a nuclear extract gave rise to three migration-retarded species specific to UAS87. Heat- or proteinase-treatment of the nuclear extract revealed that these species were protein-DNA complexes. The precise binding region of the protein identified by DNaseI protection analysis was found to include a CCAAACA sequence which forms a dyad-symmetrical structure. The amount of one of the three migration-retarded species significantly increased when cells were grown in medium containing a gluconeogenic carbon source. The introduction of pGCR8, a multicopy plasmid containing GCR1 gene, a regulatory gene controlling the expression of several glycolytic enzymes, showed no effect on the amount of three migration-retarded species. 相似文献
10.
Shinichi Ikemoto Seiji Wada Masato Kamizuru Nobuyuki Hayahara Taketoshi Kishimoto Masanobu Maekawa 《Cancer immunology, immunotherapy : CII》1992,34(5):289-293
Summary The authors examined interleukin-2 (IL-2) production and interferon (IFN) production of peripheral blood mononuclear cells in 28 patients with renal cell carcinoma and 17 control subjects. The peripheral blood was obtained prior to the initiation of therapeutic procedures. The patients were divided into two groups according to tumor size, 5 cm and >5 cm. The production of IL-2 and IFN was measured by immunoradiometric assay. As a result, in the patients with tumors >5 cm, IL-2 and IFN production was impaired. However, in the patients with tumors 5 cm, IFN production was enhanced, though IL-2 production was not significantly different from that of the control subjects. There was no significant correlation between IL-2 production and IFN production. 相似文献