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| 2. |
- Cassimjee, Karim Engelmark, et al.
(författare)
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Active Site Quantification of an omega-Transaminase by Performing a Half Transamination Reaction
- 2011
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 1:9, s. 1051-1055
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Tidskriftsartikel (refereegranskat)abstract
- Measurement of the active enzyme fraction in a given enzyme preparation is a requirement for accurate kinetic measurements and activity comparisons of, for example, engineered mutants. omega-Transaminases, enzymes capable of interconverting ketones and amines by use of pyridoxal-5'-phosphate (PIP), can be used for the production of pharmaceutically important chiral amines but are subject to engineering to meet the practical requirements in synthesis reactions. Therefore, an active site quantification method is needed. Such a method was developed by quantifying the amount of consumed substrate in a virtually irreversible half transamination reaction. (S)-1-phenylethylamine was converted to acetophenone, while the holo enzyme (E-PLP) was converted to apo enzyme with bound pyridoxamine-5'-phosphate (E:PMP). Further, the mass of active enzyme was correlated to the absorbance of the holo enzyme to achieve a direct measurement method. The active Chromobacterium violaceum omega-transaminase with bound PLP can be quantified at 395 nm with an apparent extinction coefficient of 8.1 mM(-1) cm(-1).
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| 3. |
- Cassimjee, Karim Engelmark, et al.
(författare)
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Chromobacterium violaceum omega-transaminase variant Trp60Cys shows increased specificity for (S)-1-phenylethylamine and 4 '-substituted acetophenones, and follows Swain-Lupton parameterisation
- 2012
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Ingår i: Organic and biomolecular chemistry. - : Royal Society of Chemistry (RSC). - 1477-0520 .- 1477-0539. ; 10:28, s. 5466-5470
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Tidskriftsartikel (refereegranskat)abstract
- For biocatalytic production of pharmaceutically important chiral amines the.-transaminase enzymes have proven useful. Engineering of these enzymes has to some extent been accomplished by rational design, but mostly by directed evolution. By use of a homology model a key point mutation in Chromobacterium violaceum omega-transaminase was found upon comparison with engineered variants from homologous enzymes. The variant Trp60Cys gave increased specificity for (S)-1-phenylethylamine (29-fold) and 4'-substituted acetophenones (similar to 5-fold). To further study the effect of the mutation the reaction rates were Swain-Lupton parameterised. On comparison with the wild type, reactions of the variant showed increased resonance dependence; this observation together with changed pH optimum and cofactor dependence suggests an altered reaction mechanism.
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| 4. |
- Cassimjee, Karim Engelmark, et al.
(författare)
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One-step enzyme extraction and immobilization for biocatalysis applications
- 2011
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Ingår i: Biotechnology Journal. - : Wiley. - 1860-6768 .- 1860-7314. ; 6:4, s. 463-469
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Tidskriftsartikel (refereegranskat)abstract
- An extraction/immobilization method for HIs(6) -tagged enzymes for use in synthesis applications is presented. By modifying silica oxide beads to be able to accommodate metal ions, the enzyme was tethered to the beads after adsorption of Co(II). The beads were successfully used for direct extraction of C. antarctica lipase B (CalB) from a periplasmic preparation with a minimum of 58% activity yield, creating a quick one-step extraction-immobilization protocol. This method, named HisSi Immobilization, was evaluated with five different enzymes [Candida antarctica lipase B (CalB), Bacillus subtilis lipase A (BslA), Bacillus subtilis esterase (BS2), Pseudomonas fluorescence esterase (PFE), and Solanum tuberosum epoxide hydrolase 1 (StEH1)]. Immobilized CalB was effectively employed in organic solvent (cyclohexane and acetonitrile) in a transacylation reaction and in aqueous buffer for ester hydrolysis. For the remaining enzymes some activity in organic solvent could be shown, whereas the non-immobilized enzymes were found inactive. The protocol presented in this work provides a facile immobilization method by utilization of the common His(6) -tag, offering specific and defined means of binding a protein in a specific location, which is applicable for a wide range of enzymes.
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| 5. |
- Cassimjee, Karim Engelmark, et al.
(författare)
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Silica-immobilized His(6)-tagged enzyme : Alanine racemase in hydrophobic solvent
- 2008
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 99:3, s. 712-716
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Tidskriftsartikel (refereegranskat)abstract
- A new immobilization method for enzymes is presented to facilitate synthetic applications in aqueous as well as organic media. The enzyme Alanine racemase (AlaR) from Geobacillus stearothermophilus was cloned, overexpressed and then immobilized on a silica-coated thin-layer chromatography plate to create an enzyme surface. The enzyme, fused to a His(6)-tag at its N-terminal, was tethered to the chemically modified silica-coated TLC plate through cobalt ions. The immobilized enzyme showed unaltered kinetic parameters in small-scale stirred reactions and retained its activity after rinsing, drying, freezing or immersion in n-hexane. This practical method is a first step towards a general immobilization method for synthesis applications with any enzyme suitable for His(6)-tagging.
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| 6. |
- Cassimjee, Karim Engelmark, et al.
(författare)
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Streamlined Preparation of Immobilized Candida antarctica Lipase B
- 2017
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 2:12, s. 8674-8677
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Tidskriftsartikel (refereegranskat)abstract
- Candida antarctica lipase B (CalB) was efficiently expressed (6.2 g L-1) in Escherichia coli by utilizing an N-terminal tag cassette and the XylS/Pm expression system in a fed-batch bioreactor; subsequent direct binding to EziG from crude extracts resulted in an immobilized catalyst with superior activity to Novozym 435.
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| 7. |
- Engelmark Cassimjee, Karim, et al.
(författare)
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A general protein purification and immobilization method on controlled porosity glass : biocatalytic applications
- 2014
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Ingår i: Chemical Communications. - : Royal Society of Chemistry. - 1359-7345 .- 1364-548X. ; 50:65, s. 9134-9137
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Tidskriftsartikel (refereegranskat)abstract
- A general combined purification and immobilization method to facilitate biocatalytic process development is presented. The support material, EziG (TM), is based on controlled porosity glass (CPG) or polymer-coated versions thereof (HybCPG) and binds protein affinity tags. Biocatalytic reactions in aqueous and organic media with seven enzymes of biocatalytic interest are shown.
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| 8. |
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| 9. |
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| 10. |
- Engelmark Cassimjee, Karim, et al.
(författare)
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A quantum chemical study of the ω-transaminase reaction mechanism
- 2015
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Ingår i: Organic and biomolecular chemistry. - : Royal Society of Chemistry (RSC). - 1477-0520 .- 1477-0539. ; 13:31, s. 8453-8464
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Tidskriftsartikel (refereegranskat)abstract
- ω-Transaminases are valuable tools in biocatalysis due to their stereospecificity and their broad substrate range. In the present study, the reaction mechanism of Chromobacterium violaceum ω-transaminase is investigated by means of density functional theory calculations. A large active site model is designed based on the recent X-ray crystal structure. The detailed energy profile for the half-transamination of (S)-1-phenylethylamine to acetophenone is calculated and the involved transition states and intermediates are characterized. The model suggests that the amino substrate forms an external aldimine with the coenzyme pyridoxal-5′-phosphate (PLP), through geminal diamine intermediates. The external aldimine is then deprotonated in the rate-determining step, forming a planar quinonoid intermediate. A ketimine is then formed, after which a hemiaminal is produced by the addition of water. Subsequently, the ketone product is obtained together with pyridoxamine-5′-phosphate (PMP). In the studied half-transamination reaction the ketone product is kinetically favored. The mechanism presented here will be valuable to enhance rational and semi-rational design of engineered enzyme variants in the development of ω-transaminase chemistry.
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