| 1. |
- HOLMQUIST, M, et al.
(författare)
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TRP89 IN THE LID OF HUMICOLA-LANUGINOSA LIPASE IS IMPORTANT FOR EFFICIENT HYDROLYSIS OF TRIBUTYRIN
- 1994
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Ingår i: Lipids. - : Wiley. - 0024-4201 .- 1558-9307. ; 29:9, s. 599-603
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Tidskriftsartikel (refereegranskat)abstract
- To determine whether Trp89 located in the lid of the lipase (EC 3.1.1.3) from Humicola lanuginosa is important for the catalytic property of the enzyme, site-directed mutagenesis at Trp89 was carried out. The kinetic properties of wild type and mutated enzymes were studied with tributyrin as substrate. Lipase variants in which Trp89 was changed to Phe, Leu, Gly or Glu all showed less than 14% of the activity compared to that of the wild type lipase. The Trp89Glu mutant was the least active with only 1% of the activity seen with the wild type enzyme. Ah Trp mutants had the same binding affinity to the tributyrin substrate interface as did the wild type enzyme. Wild type lipase showed saturation kinetics against tributyrin when activities were measured with mixed emulsions containing different proportions of tributyrin and the nonionic alkyl polyoxyethylene ether surfactant, Triton DF-16. Wild type enzyme showed a V-max = 6000 +/- 300 mmol.min(-1).g(-1) and an apparent K-m = 16 +/- 2% (vol/vol) for tributyrin in Triton DF-16, while the mutants did not show saturation kinetics in an identical assay. The apparent K-m for tributyrin in Triton DF-16 was increased as the result of replacing Trp89 with other residues (Phe, Leu, Gly or Glu). The activities of all mutants were more sensitive to the presence of Triton DF-16 in the tributyrin substrate than was wild type lipase. The activity of the Trp89Glu mutant was decreased to 50% in the presence of 2 vol% Triton DF-16 compared to the activity seen with pure tributyrin as substrate. Wild type lipase and all mutants except Trp89Glu had the same affinity for the substrate interface formed by 15.6 vol% tributyrin in Triton DF-16. The Trp89Glu mutant showed a lower affinity than all the other lipase variants for the interface of 15.6 vol% tributyrin in Triton DF-16. The study showed that Trp89 located in the lid of H. lanuginosa lipase is important for the efficient hydrolysis of tributyrin and that this residue plays a role in the catalytic steps after adsorption of the lipase to the substrate interface.
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| 2. |
- JOHANSSON, M, et al.
(författare)
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SYNTHESIS, CHARACTERIZATION, AND CURING OF WELL-DEFINED ALLYL ETHER-MALEATE FUNCTIONAL ESTER OLIGOMERS - LINEAR VERSUS NONLINEAR STRUCTURES
- 1992
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Ingår i: Journal of Polymer Science Part A. - : Wiley. - 0887-624X .- 1099-0518. ; 30, s. 2203-2210
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Tidskriftsartikel (refereegranskat)abstract
- A series of allyl ether-maleate functional star-shaped esters with from one to four arms has been synthesized. The structures that have been made are an analogous series with increasing molecular weight and functionality where the increase in molecular weight has been made nonlinear, i.e., star-shaped. The resins are monodisperse in the sense that each arm has a well-defined structure and that, within a certain sample, only one type of molecule exists. The viscosity and rheological behavior of the resins have been studied. The curing kinetics of the star-shaped (branched) resins and the properties of the films formed have also been studied. These properties have been related to differences in functionality and to differences in the molecular architecture of the resins.
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| 3. |
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| 4. |
- JOHANSSON, M, et al.
(författare)
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INFLUENCE OF ALLYL ETHERS IN COATING RESINS
- 1991
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Ingår i: Journal of Polymer Science Part A. - : Wiley. - 0887-624X .- 1099-0518. ; 29, s. 1639-1644
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Tidskriftsartikel (refereegranskat)abstract
- The effects of allyl ethers in coating resins have been studied in relation to different systems. The details that have been investigated are: the reactions between allyl ethers-styrene-cobalt salt in air, the influence of cobalt salt on oxidized allyl ethers, and the interaction between allyl ethers and maleic esters with respect to copolymerization. The curing rates of allyl functional oligomers as coatings have also been studied. The results are summarized together with the results from a previous article by the same authors to give an overall view of the curing mechanism in allyl ether functional unsaturated polyester resins dissolved in styrene.
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| 5. |
- JOHANSSON, M, et al.
(författare)
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INFLUENCE OF ALLYL ETHERS ON FREE-RADICAL POLYMERIZATION OF STYRENE
- 1991
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Ingår i: Journal of Polymer Science Part A. - : Wiley. - 0887-624X .- 1099-0518. ; 29, s. 9-14
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Tidskriftsartikel (refereegranskat)abstract
- The effect of allyl ethers on the free radical polymerization of styrene has been studied with respect to chain transfer, copolymerization, and conversion. The studies have been performed in an inert atmosphere or in air. Six different allyl ethers have been used as model substances in order to show the effect of structural differences of the ethers on the polymerization. Contrary to what was expected, no chain transfer through hydrogen abstraction was found. Nor did any copolymerization occur. When the polymerization was performed in air, the allyl ethers had a retarding effect on the polymerization rate, due to oxidation of the allyl ethers. The oxidation rate of the allyl ethers was found to be related to their structure, where the functionality and presence of intramolecular hydrogen bonding are the main factors.
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| 6. |
- JOHANSSON, M, et al.
(författare)
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SYNTHESIS, CHARACTERIZATION, AND CURING OF HYPERBRANCHED ALLYL ETHER MALEATE FUNCTIONAL ESTER RESINS
- 1993
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Ingår i: Journal of Polymer Science Part A. - : Wiley. - 0887-624X .- 1099-0518. ; 31, s. 619-624
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Tidskriftsartikel (refereegranskat)abstract
- A model two-step synthesis of a saturated hyperbranched hydroxyl-terminated ester has been developed to show a synthesis route. Three different series of hyperbranched esters with different terminations have been synthesized to relate some of their properties to their structures. This route has then been used to synthesize three different allyl ether-maleate functional hyperbranched ester resins in a two-step procedure. The resins have been characterized with respect to rheology, structure, and properties, and the differences are discussed. The allyl ether-maleate functional resins have also been studied with respect to curing performance and final film properties.
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| 7. |
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