| 1. |
- Akimov, D., et al.
(författare)
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Physics with WASA and PROMICE
- 1994
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Ingår i: Physics with GeV-particle beams, Juelich 1994. ; , s. 519-530
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Konferensbidrag (refereegranskat)
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| 2. |
- Le Lay, G., et al.
(författare)
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STM and synchrotron radiation studies of "prototypical" metal{plus 45 degree rule}semiconductor systems
- 1994
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Ingår i: Surface Science. - 0039-6028. ; 307-309:PART A, s. 280-294
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Tidskriftsartikel (refereegranskat)abstract
- Since the origin of surface science noble metal{plus 45 degree rule}elemental semiconductor couples have been considered as "prototypical" systems. After three decades of research their structural and electronic properties remain an intriguing maze despite recent advances made, especially thanks to the development of the near-field microscopies and the extensive use of synchrotron radiation in surface crystallography and in high-resolution photoelectron spectroscopy. In the last few years, lead, as a replacement inert metal, has nearly gained the pole position in the display of exotic behaviour. This paper gives a flavour of this mystery story and highlights some puzzling questions. © 1994.
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| 3. |
- Axelsson, Kennet, et al.
(författare)
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Determination of constitutive parameters for soils based on optimization
- 1991
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Ingår i: Computer methods and advances in geomechanics. - Rotterdam : Balkema Publishers, A.A. / Taylor & Francis The Netherlands. - 9061911893 ; , s. 569-574
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Konferensbidrag (refereegranskat)abstract
- Optimization-based methods for the determination of constitutive parameters of material models are evaluated. Rosenbrock's and Levenberg-Marquardt's algorithms are considered in particular. Based on experimental data for Swedish silt, two plasticity models are calibrated and their performances are compared
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| 4. |
- Gololobov, M. Yu, et al.
(författare)
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Influence of Organic Solvents on the Specificity of α-Chymotrypsin and Subtilisin from B. Subtilis Strain 72 in Acyl Transfer Reactions
- 1992. - C
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Ingår i: Progress in Biotechnology. - 0921-0423. ; 8:C, s. 435-442
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Bokkapitel (refereegranskat)abstract
- Nucleophilic properties of amino acid amides were studied systematically in acyl-transfer reactions catalyzed by α-chymotrypsin and subtilisin from Bacillus subtilis strain 72 (subtilisin 72) using Mal-L-Ala-L-Ala-L-PheOMe and Bz-L-TyrOme as the acyl group donors. In α-chymotrypsin-catalyzed reactions in water the reactivity of the amino acid amides increases with hydrophobicity of the nucleophiles. Hydrophobic interactions in this case are responsible for the differences between the reactivity of the nucleophiles for amides of all the amino acids tested with the exception of D-AlaNH2 and L-ArgNH2. In a low water system (4% of H2O, 47.5% of acetonitrile, 47.5% of dimethyl formamide, 1% of (C2H5)3N) the specificity of α-chymotrypsin towards the amino acid amides in acyl transfer reactions decreases and does not depend on the amino acid side chain hydrophobicity. The specificity in this case correlates with the bulk characteristics of the amino acid side chains (normalized van der Waals volume, polarizability, molecular weight). The bulky amino acid amides are less efficient nucleophiles. In reactions catalyzed by subtilisin 72, amino acid side chain characteristics do not correlate with the nucleophile reactivities. The data obtained show that different factors may be responsible for the specificity of enzymes in water and in low water systems and in general, specificity patterns obtained in water can not be used for low water systems.
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| 5. |
- Gololobov, Mikhail Yu, et al.
(författare)
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Nucleophile specificity in α-chymotrypsin- and subtilisin-(Bacillus subtilis strain 72) catalyzed reactions
- 1992
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Ingår i: BBA - Protein Structure and Molecular Enzymology. - 0167-4838. ; 1160:2, s. 188-192
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Tidskriftsartikel (refereegranskat)abstract
- Nucleophilic properties of amino-acids were studied systematically in acyl-transfer reactions catalyzed by α-chymotrypsin and subtilisin from Bacillus subtilis strain 72 (subtilisin 72) using Mal-l-Ala-l-Ala-l-PheOMe as the acyl-group donor. In α-chymotrypsin-catalyzed reactions, the nucleophile reactivities increase in the following order: d-AlaNH2 < GlyNH2 < l-AlaNH2 < l-ScrNH2 < l-ThrNH2 < l-HisNH2 < l-ValNH2 < l-LcuNH2 < l-TrpNH2 < l-MetNH2 < l-NvaNH2 < l-PheNH2 < l-IleNH2 < l-TyrNH2 < l-ArgNH2. In reactions catalyzed by subtilisin 72, the reactivities increase as follows: l-LeuNH2 < l- IleNH2 < l-ThrNH2 < l-ArgNH2 < l-TrpNH2 < l-NvaNH2 < l-ValNH2 < l-MctNH2 < l-AlaNH2 < l-ScrNH2 < d-AlaNH2 < GlyNH2. In α-chymotrypsin-catalyzed reactions, hydrophobic interactions are entirely responsible for the differences between the reactivity of the nucleophiles for amides of all the amino-acids tested with the exception of d-AlaNH2, l-ArgNH2 and l-TyrNH2. In the reactions catalyzed by subtilisin 72, Amino-acid side-chain characteristics and the nucleophile reactivities are not related. The data obtained show the low selectivity of the S1′ subsite of subtilisin 72 and high specify of this subsite in α-chymotrypsin.
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| 6. |
- Gololobov, Mikhail Yu, et al.
(författare)
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Organic solvent changes the chymotrypsin specificity with respect to nucleophiles
- 1992
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Ingår i: FEBS Letters. - 0014-5793. ; 307:3, s. 309-312
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Tidskriftsartikel (refereegranskat)abstract
- In α-chymotrypsin-catalyzed acyl-transfer reactions in water the specificity of the enzyme (the nucleophile reactivity of amino acid amides) is correlated with the substrate hydrophobicity and increases as the hydrophobicity of the side chain of the amino acid amides is increased. In a low water system (4% H2O) bulky amino acid amides are less efficient nucleophiles. The specificity of α-chymotrypsin towards the amino acid amides in acyl transfer reactions in this case does not depend on the hydrophobicity of the amino acid side chains but correlates with their size. Therefore, different factors can be responsible for the specificity of enzymes in water and in a mainly organic medium.
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| 7. |
- Gololobov, Mikhail Yu, et al.
(författare)
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Side reactions in enzymatic peptide synthesis in organic media : Effects of enzyme, solvent, and substrate concentrations
- 1994
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Ingår i: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229. ; 16:6, s. 522-528
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Tidskriftsartikel (refereegranskat)abstract
- The progress of enzymatic peptide synthesis catalyzed by α-chymotrypsin and subtilisin from Bacillus subtilis strain 72 (subtilisin 72) in low-water systems was studied. The initial reaction mixture consisted of the solvent, the acyl-group donor (MalAlaAlaPheOMe or ZAlaAlaPheOMe, Mal, maleyl, Z, benzyloxycarbonyl), the nucleophile XaaNH2 (Xaa = Phe, Leu or Ala), and the enzyme adsorbed on porous silica material. All amino acid residues were of the l-configuration. The solvent consisted of acetonitrile, dimethylformamide (DMF), and 4% (v/v) of water. The DMF/acetonitrile ratio was varied between 0 and 1/1. At high concentration of the acyl-group donor and approximately equimolar ratio of the nucleophile and the acyl-group donor, quantitative formation of MalAlaAlaPheXaaNH2 or ZAlaAlaPheXaaNH2 occurred. As a result, a method for the synthesis of polypeptide amides was developed. At low concentration of the acyl-group donor and excess of the nucleophile, the condensation by-products with two and three nucleophile molecules were found in the reaction mixtures. The data obtained provided evidence that organic solvents affected the S'1-specificity of α-chymotrypsin and the Sl-specificity of subtilisin 72, while the Sl-specificity of α-chymotrypsin and the S'l-specificity of subtilisin 72 were not affected. When the DMF content was increased, the rate of the α-chymotrypsin-catalyzed reactions decreased. In contrast to this, an increase in DMF content accelerated the subtilisin 72-catalyzed reactions. Hydrolysis of the acyl-group donor did not occur in the α-chymotrypsin-catalyzed reactions. Significant (up to 50%) formation of MalAlaAlaPheOH was observed a the early stage of the subtilisin 72-catalyzed reactions. Later MalAlaAlaPheOH underwent synthesis.
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| 8. |
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