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  • organic solvents  (9)
  • Wiley-Blackwell  (8)
  • Elsevier  (1)
  • Periodicals Archive Online (PAO)
  • 1
    Electronic Resource
    Electronic Resource
    Kinetic analysis of the mechanism for subtilisin in essentially anhydrous organic solvents
    Amsterdam : Elsevier
    Enzyme and Microbial Technology 15 (1993), S. 1022-1029 
    Details
    ISSN: 0141-0229
    Keywords: Enzymes ; active site titration ; mechanism ; microscopic rate constants ; organic solvents ; subtilisin
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0141-0229(93)90049-8
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  • 2
    Electronic Resource
    Electronic Resource
    Biocatalytic synthesis of acrylates in organic solvents and supercritical fluids: III. Does carbon dioxide covalently modify enzymes? (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 46 (1995), S. 610-620 
    Details
    ISSN: 0006-3592
    Keywords: enzymes ; organic solvents ; supercritical fluids ; carbon dioxide ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We have previously demonstrated that the activity of the lipase (Candida cylindracea) catalyzed transesterification reaction between methylmethacrylate and 2-ethylhexanol in supercritical carbon dioxide is comparatively low. In this article, we have investigated the same reaction in supercritical carbon dioxide with a special emphasis on determining the extent of any interaction between the enzyme and carbon dioxide. Transesterification reaction rates in hexane and supercritical carbon dioxide are compared at different temperatures. In supercritical carbon dioxide, temperature was found to have no significant effect on reaction rate in the range of 40° to 55°C. Above 55°C, however, the reaction rate increased significantly as a function of temperature. It appears that carbon dioxide forms reversible complexes with the free amine groups on the surface of the enzyme. Direct evidence of modification was obtained using mass spectroscopy to detect the extent of modification of a pure protein. The kinetics of the reaction have been studied in hexane, and they obey a ping-pong bi-bi mechanism with inhibition by 2-ethylhexanol. The effect of bubbling carbon dioxide and/or fluoroform on the reaction rate in hexane at different temperatures suggests that the enzyme undergoes shear inactivation in hexane. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260460614
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  • 3
    Electronic Resource
    Electronic Resource
    A comparison of lipase-catalyzed ester hydrolysis in reverse micelles, organic solvents, and biphasic systems (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 47 (1995), S. 60-70 
    Details
    ISSN: 0006-3592
    Keywords: enzymes ; organic solvents ; lipase ; reverse micelles ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The performance of lipases from Candida rugosa and wheat germ have been investigated in three reaction media using three acetate hydrolyses as model reactions (ethyl acetate, allyl acetate, and prenyl acetate). The effect of substrate properties and water content were studied for each system (organic solvent, biphasic system, and reverse micelles). Not unexpectedly, the effect of water content is distinct for each system, and the optimal water content for enzyme activity is not always the same as that for productivity. A theoretical model has been used to simulate and predict enzyme performance in reverse micelles, and a proposed partitioning model for biphasic systems agrees well with experimental results. While the highest activities observed were in the micellar system, productivity in microemulsions is limited by low enzyme concentrations. Biphasic systems, however, support relatively good activity and productivity. The addition of water to dry organic solvents, combined with the dispersion of lyophilized enzyme powders in the solvent, resulted in significant enzyme aggregation, which not surprisingly limits the applicability of the “anhydrous” enzyme suspension approach. © 1995 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260470108
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of hydration on the morphology of enzyme powder (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 39 (1992), S. 1171-1175 
    Details
    ISSN: 0006-3592
    Keywords: enzymes ; organic solvents ; hydration ; environmental electron microscopy ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We report the first direct images of the hydration of protein powders. Using an environmental scanning electron microscope (ESEM) we have taken a series of micrographs of a region of the enzyme (subtilisin) power whilst hydrating the sample. In addition, the sample has been viewed during exposure to toluene vapors. The ESEM is a remarkable new instrument that will have wide applicability in imaging of biological materials in their native environments.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260391114
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  • 5
    Electronic Resource
    Electronic Resource
    Biocatalytic synthesis of acrylates in organic solvents and supercritical fluids: I. Optimization of enzyme environment (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 40 (1992), S. 158-166 
    Details
    ISSN: 0006-3592
    Keywords: enzymes ; organic solvents ; supercritical fluids ; acrylates ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Biocatalytic transesterification of methylmethacrylate is possible in many different solvents. The reaction rate is readily controlled by variation in solvent physical properties. The reaction proceeds better in hydrophobic solvents, and activity can be restored in hydrophilic solvents by the addition of water. We have now demonstrated that supercritical carbon dioxide is not a good solvent for the reaction between 2-ethlhexanol and methylmethacrylate. It apperars that the supercritical carbon dioxide may either alter the pH of the microaqueous environment associated with the protein or reversibly form covalent complexes with free amine groups on the surface of the enzyme. Although supercritical carbon dioxide is a poor solvent for acrylate transesterification, many other supercritical fluids (ethane, ethylene, sulfur hexafluoride, and fluoroform) are better than most conventional solvents. In supercritical ethane it is possible to control the activity of the enzyme by changing pressure, and the enzyme appears to follow Michaelis-Menten Kinetics. We find that sulfur hexafluoride, the first anhydrous inorganic solvent in which biocatalytic activity has been reported, is a better solvent than any conventional or supercritical organic fluid tested.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260400122
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  • 6
    Electronic Resource
    Electronic Resource
    Protein extraction and activity in reverse micelles of a nonionic detergent (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 39 (1992), S. 806-814 
    Details
    ISSN: 0006-3592
    Keywords: enzymes ; proteins ; organic solvents ; microemulsions ; nonionic surfactants ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We describe, for the first time, the ability of a polyoxyethylene sorbitan trioleate-isopropanol microemulsion in hexane to solubilize pure proteins. The dependences of cytochrome c extraction and buffer solubilization by the reverse micellar system on ionic strength of the aqueous phase, detergent concentration, and cosurfactant concentration result in increased extraction. In addition, subtilisin (a serine protease) is shown to be active in this microemulsion. Further the activity of the enzyme can be regulated by the water content of the micelles, enabling control of enzyme activity by “solvent engineering.”
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260390803
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  • 7
    Electronic Resource
    Electronic Resource
    Determination of equilibrium and individual rate constants for subtilisin-catalyzed transesterification in anhydrous environments (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 40 (1992), S. 1069-1077 
    Details
    ISSN: 0006-3592
    Keywords: enzymes ; organic solvents ; mechanism ; subtilisin ; microscopic rate constants ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We report here the first determinations of individual rate constants and equilibrium constants for enzymatic reactions in essentially anhydrous organic solvents. Using the added nucleophile method we have measured the effect of changing solvent on the binding and catalytic steps for subtilisin-catalyzed transesterification of N-protected amino acid esters. The detailed information generated indicates that once the substrate has bound to the enzyme, the catalytic machinery can work at rates equivalent to those in water. The decreased overall rates for subtilisin suspended in anhydrous solvents are merely the result of extremely high values for Ks, in most cases, coupled with low concentrations of nucleophile (∼1.0M in organic solvents, and 55M in water). The method described, which is generally applicable, and straightforward experimentally, will, we believe, enable a clearer understanding of how changing solvent can predictably affect the activity and specificity of the enzyme. © 1992 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260400910
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  • 8
    Electronic Resource
    Electronic Resource
    Two-Step biocatalytic conversion of an ester to an aldehyde in reverse micelles (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 232-241 
    Details
    ISSN: 0006-3592
    Keywords: enzymes ; organic solvents ; alcohol dehydrogenase ; reverse micelles ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Lipases from Candida cyclindracea (L-1754) and wheat germ (L-3001) have been used to hydrolyze esters to their corresponding alcohols and acids in reverse micelles. Alcohol dehydrogenase from baker's yeast (YADH) was subsequently used to reduce the alcohol products to aldehydes. Cofactor recycling in the redox reaction was achieved using a sacrificial cosubstrate, as described previously. Four surfactants (sodium dioctylsulfosuccinate, Nonidet P-40 with Triton X-35, polyoxyethylene, 10-cetyl-ether, polyoxyethylene sorbitan trioleate) were employed to determine the effect of amphiphile on ester hydrolysis and redox reaction rates separately. The effect of type of organic solvent, W0 [(water]/[surfactant)], and substrate concentration on separte enzyme activity were also investigated. A brief investigation of a single phase, two-step reaction catalyzed by the combination of lipase and YADH in reverse micelles is also reported. The activities of the enzymes are significantly different when used together instead of independently. © 1994 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260430307
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  • 9
    Electronic Resource
    Electronic Resource
    High pressure EPR studies of protein mobility in reversed micelles (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 342-348 
    Details
    ISSN: 0006-3592
    Keywords: organic solvents ; reversed micelles ; protein mobility ; EPR spectra of enzymes ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We have investigated the effect of pressure on structural properties of subtilisin solubilized in reversed micelles of Tween-85/isopropanol in hexane. Electron paramagnetic resonance (EPR) spectra of spin-labeled enzyme indicate a reduction in spin-label mobility when the enzyme is transferred from aqueous solution to the microemulsion. One explanation for the spectral broadening is a change in the protein's active-site conformation and/or dynamics. However, over a W0 range of 80 to 180, EPR spectroscopy could detect no change in the enzyme's environment, conformation, or molecular dynamics. The EPR spectra also contained a contribution from free spin label located in an environment with a polarity roughly between that of propanol and bulk water. No changes in the polarity surrounding the free spin label nor in the enzyme's structural properties were evident at pressures up to 10,000 psi. Previous work has demonstrated that pressure can be used to manipulate the size of some reversed micelles, and the EPR data indicated that for this system such pressure tuning of micellar properties will not adversely affect the structure of solubilized enzyme. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260430412
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