Metathesis of Alkanes Catalyzed by Silica-Supported Transition Metal Hydrides     

V Vidal  A Theolier  J Thivolle-Cazat  JM Basset 《Science (New York, N.Y.)》1997,276(5309):99-102

The silica-supported transition metal hydrides (=Si-O-Si=)(=Si-O-)2Ta-H and (=Si-O-)xM-H (M, chromium or tungsten) catalyze the metathesis reaction of linear or branched alkanes into the next higher and lower alkanes at moderate temperature (25degrees to 200degreesC). With (=Si-O-Si=)(=Si-O-)2Ta-H, ethane was transformed at room temperature into an equimolar mixture of propane and methane. Higher and lower homologs were obtained from propane, butane, and pentane as well as from branched alkanes such as isobutane and isopentane. The mechanism of the step leading to carbon-carbon bond cleavage and formation likely involves a four-centered transition state between a tantalum-alkyl intermediate and a carbon-carbon final sigma-bond of a second molecule of alkane.  相似文献   

A cytoplasmic protein inhibits the GTPase activity of H-Ras in a phospholipid-dependent manner   总被引：8，自引：0，他引：8  

M H Tsai  C L Yu  D W Stacey 《Science (New York, N.Y.)》1990,250(4983):982-985

A cytoplasmic protein has been identified that inhibits the guanosine triphosphatase (GTPase) activity of bacterially synthesized, cellular H-Ras protein. This GTPase inhibiting protein is able to counteract the activity of GTPase activating protein (GAP), which has been postulated to function as a negative regulator of Ras activity. The potential biological importance of the GTPase inhibiting protein is further supported by its interaction with lipids. Phospholipids produced in cells as a consequence of mitogenic stimulation increase the activity of the GTPase inhibiting protein, as well as inhibit the activity of GAP. The interaction of such lipids with each of these two regulatory proteins would, therefore, tend to increase the biological activity of Ras and stimulate cell proliferation.  相似文献   

Mineral inclusions in diamond: temperature and pressure of equilibration     

Meyer HO  Tsai HM 《Science (New York, N.Y.)》1976,191(4229):849-851

Two distinct suites of minerals included in natural diamond occur and probably represent different physical and chemical conditions during diamond growth. Minerals of the ultramafic suite appear to have equilibrated in the range 1000 degrees to 1300 degrees C between 45 and 65 kilobars, whereas the temperature range for minerals of the eclogitic suite is 850 degrees to 1250 degrees C. At present, models relating the partitioning of magnesium and iron between coexisting phases are not sufficiently rigorous to determine a value for the pressure of equilibration of these eclogitic suite inclusions.  相似文献   

VITAMIN B DEFICIENCY IN NURSING YOUNG RATS AND LEARNING ABILITY     

Maurer S  Tsai LS 《Science (New York, N.Y.)》1929,70(1819):456-458

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Spatial Variability of Turbulent Mixing in the Abyssal Ocean   总被引：3，自引：0，他引：3  

KL Polzin  JM Toole  JR Ledwell  RW Schmitt 《Science (New York, N.Y.)》1997,276(5309):93-96

Ocean microstructure data show that turbulent mixing in the deep Brazil Basin of the South Atlantic Ocean is weak at all depths above smooth abyssal plains and the South American Continental Rise. The diapycnal diffusivity there was estimated to be less than or approximately equal to 0.1 x 10(-4) meters squared per second. In contrast, mixing rates are large throughout the water column above the rough Mid-Atlantic Ridge, and the diffusivity deduced for the bottom-most 150 meters exceeds 5 x 10(-4) meters squared per second. Such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry.  相似文献   

Parthenogenesis, polyploidy and reproductive seasonality in the Taiwanese mountain earthworm Amynthas catenus (Oligochaeta, Megascolecidae)     

Huei-Ping Shen  Chu-Fa Tsai  Jiun-Hong Chen 《Pedobiologia》2011,54(2):133-139

Amynthas catenusTsai et al., 2001 is a terrestrial earthworm belonging to the Pheretima complex of the family Megascolecidae. It is endemic to Mt. Hohuan of central Taiwan at elevations of 2985-3004 m. Its reproductive organs showed various stages of degeneration in the present study. The spermathecae varied from being absent (athecal) to three pairs in VI-VIII (sexthecal), and the prostate glands from a large, symmetrical pair to complete absence. For the 44 specimens examined from May 2008 to May 2010, there were 47.7% athecals, 36.4% sexthecals and 15.9% intermediates. Results of a flow cytometric analysis showed that there were three DNA ploidy levels - diploid, triploid and tetraploid (2n, 3n, and 4n) - for the athecals but only diploid for the sexthecals. The intermediates consisted of diploids and triploids. The diploids had 2n = 112 and the triploids 3n = 168. The haploid chromosome number of A. catenus was 56. Spermatogenesis occurred throughout the year with the highest activity in summer for both athecals and sexthecals, but the number of mature ova peaked in summer for the athecals and in spring for the sexthecals. There was no significant difference in mean number of mature ova produced between the athecals and the sexthecals, but the sexthecals had significantly higher spermatogenetic activity than the athecals. For all specimens examined, sperm were present in testes and seminal vesicles but not in spermathecae, an indication of parthenogenesis in the species.  相似文献   

Identification and anti-human glioblastoma activity of tagitinin C from Tithonia diversifolia methanolic extract     

Lee MY  Liao MH  Tsai YN  Chiu KH  Wen HC 《Journal of agricultural and food chemistry》2011,59(6):2347-2355

The Tithonia diversifolia methanolic extract (TDM), which showed antiproliferative activity against human glioblastoma U373 cells, with an IC50 value of 59.2±3.7 μg mL(-1), was passed through silica gel chromatography and successively eluted with different percentages of EtOAc/hexane. The 10-60% EtOAc/hexane subfractions, which exhibited a comparatively higher antiproliferative activity, were isolated, and then structural identification was proceeded with 1H nuclear magnetic resonance. The isolated compound was tagitinin C, a kind of sesquiterpenoid. The IC50 value was 6.1±0.1 μg mL(-1) in U373 treated with tagitinin C. In flow cytometric analysis and inhibition of pan-caspase, the results showed that the anti-glioblastoma effect was apoptosis-independent. In PARP, p-p38, ULK1, and LC3-II expression, the anti-glioblastoma induced by tagitinin C was likely via autophagy. In the ULK1 siRNA transfection experiment, autophagy blockade counteracted the suppression induced by tagitinin C. The result suggested that tagitinin C induces U373 cell death dependent upon autophagy under certain conditions.  相似文献   

Temporal distribution and pathogenicity of the predominant tomato‐infecting begomoviruses in Taiwan     

W. S. Tsai  S. L. Shih  L. Kenyon  S. K. Green  F.‐J. Jan 《Plant pathology》2011,60(4):787-799

Between 1998 and 2009, the four tomato‐infecting begomovirus species detected in Taiwan were Ageratum yellow vein Hualien virus (AYVHuV), Tomato leaf curl Taiwan virus (ToLCTWV), Tomato yellow leaf curl Thailand virus (TYLCTHV) and a newly defined species Tomato leaf curl Hsinchu virus (ToLCHsV). AYVHuV was detected occasionally in 2003 and ToLCHsV only in 2000–2001, whilst ToLCTWV was detected throughout the period. TYLCTHV was first detected in 2005. Between 1998 and 2005, >99% of the begomovirus‐positive samples were infected with ToLCTWV. In 2007 in western Taiwan, 16% of the positive samples were infected with ToLCTWV, 35% with TYLCTHV and 49% with mixed infection (ToLCTWV/TYLCTHV). In contrast, in eastern Taiwan the proportions were 84% ToLCTWV, 2% TYLCTHV and 14% mixed infection. However, throughout Taiwan in 2008–2009, most positive samples were either identified as TYLCTHV (51%) or mixed infection (ToLCTWV/TYLCTHV; 41%), and only 8% were ToLCTWV. This shows a clear trend of shifting from ToLCTWV to TYLCTHV and mixed infection over a short time period in Taiwan. Sequence analyses indicated that tomato‐infecting AYVHuV, an apparent recombinant between ToLCTWV and AYVHuV from Ageratum, represents a new strain Hsinchu. TYLCTHV Taiwan isolates were highly similar to each other, whereas ToLCTWV isolates had greater diversity and were classified into three strains which had one country‐wide and two local distributions. ToLCTWV and TYLCTHV were confirmed as monopartite and bipartite begomoviruses, respectively, by agroinfection followed by transmission with Bemisia tabaci biotype B. In addition, TYLCTHV was found to be mechanically transmissible together with viral DNA‐B.  相似文献   

Application potency of engineered G159 mutants on P1 substrate pocket of subtilisin YaB as improved meat tenderizers   总被引：3，自引：0，他引：3  

Yeh CM  Yang MC  Tsai YC 《Journal of agricultural and food chemistry》2002,50(21):6199-6204

A serine protease, subtilisin YaB, produced by alkalophilic Bacillus YaB, shows promises as a potent meat tenderizer, because its substrate specificity is for small amino acids, which are found at high levels in meat connective tissue proteins. Substrate specificity engineering of the substrate binding pockets was used to generate more suitable meat-tenderizing mutants, G124A, G124V, G159A, and G159S, derived from recombinant wild subtilisin YaB and expressed in Bacillus subtilis DB104. The characteristics of these recombinant enzymes were studied to evaluate their usefulness as improved meat tenderizers. The proteolytic activities of recombinant subtilisin YaB, engineered subtilisin YaBs, and commercially available papain, bromelain, collagenase, and elastase were compared using elastin, collagen, casein, and myofibrillar proteins as substrates. Hydrolysis of beef proteins was evaluated using the myofibrillar fragmentation index and collagen solubility. The results demonstrated that recombinant mutant G159A was the most improved meat tenderizer and can be used in the meat pH range of 5.5-6.0 and the temperature range of 10-50 degrees C. Contrary to the result obtained from artificial substrate, mutant enzymes engineered on G124 residues did not exhibit better tenderizing ability when elastin, collagen, or meat was used as substrate, suggesting the necessity of evaluation by real substrate before protein-engineered enzymes are applied commercially.  相似文献   

Interferon induction in dogs.     

S C Tsai  M J Appel 《American journal of veterinary research》1979,40(3):356-361

A synthetic complex of poly (I)-poly (C) with poly-L-lysine and carboxymethyl cellulose (poly ICLC), as well as UV-inactivated Newcastle disease virus, B-1 strain, was used to induce interferon production in dogs. Several criteria were used for interferon specificity. The interferon response depended on dosage and route of inoculation. Serum interferon concentrations usually reached a peak by 8 hours after inoculation (AI), rapidly declined thereafter, and were nondetectable in most instances at 24 hours AI. Dogs responded less to interferon inducers when reinoculated 2 days after primary induction. The interferon response was biphasic (2 and 8 hours AI) when reinoculated 1 week after primary inoculation. Reinoculation 2 weeks after primary inoculation simulated the first response. Although both inducers caused severe lymphopenia in dogs, the toxic side effects would limit clinical use (in dogs) of poly ICLC, but not of UV-inactivated Newcastle disease virus.  相似文献