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101.
Thomas Janette A.; Arnold John R.P.; Basran Jaswir; Andrews Julie; Roberts Gordon C.K.; Birdsall Berry; Feeney James 《Protein engineering, design & selection : PEDS》1994,7(6):783-792
A mutant of Lactobacillus casei dihydrofolate reductase hasbeen constructed in which Thr63, a residue which interacts withthe 2'-phosphate group of the bound coenzyme, is replaced byalanine. This substitution does not affect kcat, but producesan 800-fold increase in the Km for NADPH, which reflects dissociationof NADPH from the enzyme-NADPH-tetrahydrofolate complex, anda 625-fold increase (corresponding to 3.8 kcal/mol) in the dissociationconstant for the enzyme-NADPH complex. The difference in magnitudeof these effects indicates a small effect of the substitutionon the negative cooperativity between NADPH and tetrahydrofolate.Stopped-flow studies of the kinetics of NADPH binding show thatthe weaker binding arises predominantly from a decrease in theassociation rate constant. NMR spectroscopy was used to comparethe structures of the mutant and wild-type enzymes in solution,in their complexes with methotrexate and with methotrexate andNADPH. This showed that only minimal structural changes resultfrom the mutation; a total of 47 residues were monitored fromtheir resolved 1H resonances, and of these nine in the binarycomplex and six in the ternary differed in chemical shift betweenmutant and wild-type enzyme. These affected residues are confinedto the immediate vicinity of residue 63. There is a substantialdifference in the 31P chemical shift of the 2'-phosphate ofthe bound coenzyme, reflecting the loss of the interaction withthe side chain of Thr63. The only changes in nuclear Overhausereffects (NOEs) observed were decreases in the intensity of NOEsbetween protons of the adenine ring of the bound coenzyme andthe nearby residues Leu62 and Ile102, showing that the substitutionof Thr63 does cause a change in the position or orientationof the adenine ring in its binding site. 相似文献
102.
Magnetic particles for sugar separation from sulphuric acid solution generated during nano‐crystalline cellulose production 下载免费PDF全文
Nano‐crystalline cellulose (NCC) is a renewable material having different applications ranging from drug delivery to a reinforcing filling agent in polymer synthesis. Concentrated sulphuric acid is used to hydrolyze cellulosic biomass to obtain NCC. Manufacturers are keen to reuse the diluted acid solution left after the process. However, the presence of mono and oligosaccharides makes it unsuitable for repeated use. About 99 % of these compounds have been successfully separated from the acid solution by employing NaOH‐treated magnetic particles developed during this investigation. It has been observed that by NaOH treatment, zeta potential of the magnetic particles could be increased from +11 mV to +37.5 mV; correspondingly, sugar removal efficiency was increased from 23.04 % to more than 99 %. Thus a direct correlation between the change in zeta potential of the particles and sugar separation efficiency has been observed. 相似文献
103.
104.
In vitro digestibility of starch from tepary bean, Phaseolus acutifolius var. latifolius, was determined in comparison with tepary bean flour and maize starch. The extent of sample hydrolysis by α-amylase was measured as mg reducing sugar (maltose) released per 100 mg substrate. After 2 h incubation at 37°C, values obtained for tepary starch, tepary flour and maize starch treated in various ways were as follows: raw 8.0, 8.6 and 25.6; freeze dried 2.6, 3.2 and 17.8; autoclaved 7.4, 5.7 and 27.7; cooked (15 min) 81.7, 23.1 and 87.8; resp. Raw tepary starch was more resistant to hydrolysis than maize starch due, perhaps, to differences in granule structure and amylose content. Freeze-drying and autoclaving slightly decreased digestibility of both tepary starch and flour. Cooking greatly increased susceptibility to hydrolysis for each substrate. The rate of increase was reduced after 15 min exposure to enzymes, and no appreciable difference was found between cooked tepary and maize starches. 相似文献
105.
F.J. Berry I.S. Lyubutin E.A. Moore M.F. Thomas T.V. Dmitrieva 《Materials Chemistry and Physics》2009,113(2-3):714-716
The tin-doped sulphur-containing compound of composition Fe1.05Cr1.90Sn0.05S4, in which tin is located on the octahedral sites as Sn(IV) in the spinel-related structure, has been examined by 119Sn Mössbauer spectroscopy. The data complement results obtained by 57Fe Mössbauer spectroscopy and show that tin doping increases the magnetic ordering temperature of pure FeCr2S4. These results are compared with the data obtained on tin-doped CuCr2X4 compounds (X = O, S, Se). 相似文献
106.
Grimshaw Andrew Morgan Mark Merrill Duane Kishimoto Hiro Savva Andreas Snelling David Smith Chris Berry Dave 《Computer》2009,42(2):27-34
To expand the use of distributed computer infrastructures as well as facilitate grid interoperability, OGSA has developed standards and specifications that address a range of scenarios, including high-throughput computing, federated data management, and service mobility. 相似文献
107.
J.B. Jordon M.F. Horstemeyer K. Solanki J.D. Bernard J.T. Berry T.N. Williams 《Materials Science and Engineering: A》2009,527(1-2):169-178
In this paper, the damage-induced anisotropy arising from material microstructure heterogeneities at two different length scales was characterized and modeled for a wrought aluminum alloy. Experiments were performed on a 7075-T651 aluminum alloy plate using sub-standard tensile specimens in three different orientations with respect to the rolling direction. Scanning electron microscopy was employed to characterize the stereology of the final damage state in terms of cracked and or debonded particles. A physically motivated internal state variable continuum model was used to predict fracture by incorporating material microstructural features. The continuum model showed good comparisons to the experimental data by capturing the damage-induced anisotropic material response. Estimations of the mechanical stress–strain response, material damage histories, and final failure were numerically calculated and experimentally validated thus demonstrating that the final failure state was strongly dependent on the constituent particle morphology. 相似文献
108.
Minimum substrate loss is required for resist strip of high dose, ultra shallow junction implant for source/drain extensions. Silicon surface oxidation of downstream plasma resist strip results in silicon recess of the source/drain extension regions. This paper reports the study of silicon surface oxidation for different resist strip plasma chemistries and the effect of plasma strip process parameters such as power, pressure and temperature on silicon surface oxidation. A good agreement was found between optical ellipsometry, XPS (X-ray photoelectron spectroscopy) and TEM (transmission electron spectroscopy) for thickness measurement of very thin (<20 Å) oxide grown on silicon surface due to plasma exposure. Selectivity of crust breakthrough and resist removal over silicon oxidation was also discussed in this paper along with dopant loss. 相似文献
109.
Bruce Moon Mike Berry Stephen Harris Ray Wyatt Kim Dovey Michelle Bennett 《Urban Policy and Research》2013,31(2):247-276
Australian Environmental Policy 2: Studies in Decline and Devolution Ken Walker and Kate Crowley (eds) UNSW Press, Sydney, 1999 ISBN 0868406732 (paperback) 323 pp.; bibliography and index RRP $35.00 Beyond Meltdown: The Global Battle for Sustained Growth. Peter Brain. Scribe, Melbourne, 1999 ISBN 0908011369 (paperback) 273 pp.; bibliography and index RRP $26.95 Cities Back from the Edge: New Life for Downtown Roberta Brandes Gratz with Norman Mintz John Wiley & Sons, New York, 1998 ISBN 0471144177 (hardback) 347 pp.; index RRP $59.95 Evaluation in Planning: Facing the Challenge of Complexity Nathaniel Lichfield, Angela Barbanente, Dino Bori, Abdul Khakee and Anna. Prat (eds). Kluwer, Dordrecht, 1998. ISBN 0792351770 (hardback). 383 pp.; index. RRP $254.00 Gritty Cities: Images of the Urban Lyaranette Finch and Chris McConville (eds). Pluto, Sydney, 1999. ISBN 1864030631 (paperback). 250 pp.; bibliography and index. RRP $24.95 Setting the Stage for Systainability: A Citizen's Handbook Chris Maser, Russ Beaton and Kevin Smith Lewis Publishers, Boca Raton, 1998 ISBN 1574441876 (hardback) 269 pp.; index RRP $47.50 The Australian Metropolis: A Planning History Stephen Hamnett and Robert Freestone (eds) Allen & Unwin, Sydney, 1999 ISBN 1865080535 (paperback) 229 pp.; index RRP $35.00 相似文献
110.