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- Lindkvist, B, et al.
(författare)
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Glutathione transferase mimics: micellar catalysis of an enzymic reaction
- 1997
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Ingår i: The Biochemical journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 323323 ( Pt 1), s. 39-43
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Tidskriftsartikel (refereegranskat)abstract
- Substances that mimic the enzyme action of glutathione transferases (which serve in detoxification) are described. These micellar catalysts enhance the reaction rate between thiols and activated halogenated nitroarenes as well as α,β-unsaturated carbonyls. The nucleophilic aromatic substitution reaction is enhanced by the following surfactants in descending order: poly(dimethyldiallylammonium-co-dodecylmethyldiallylammon ium) bromide (86/14) ≫cetyltrimethylammonium bromide > zwittergent 3-16 (n-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulphonate) > zwittergent 3-14 (n-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulphonate) ≈ N,N-dimethyl-laurylamine N-oxide > N,N-dimethyloctylamine N-oxide. The most efficient catalyst studied is a polymeric material that incorporates surfactant properties (n-dodecylmethyldiallylammonium bromide) and opens up possibilities for engineering sequences of reactions on a polymeric support. Michael addition to α,β-unsaturated carbonyls is exemplified by a model substance, trans-4-phenylbut-3-en-2-one, and a toxic compound that is formed during oxidative stress, 4-hydroxy-2-undecenal. The latter compound is conjugated with the highest efficiency of those tested. Micellar catalysts can thus be viewed as simple models for the glutathione transferases highlighting the influence of a positive electrostatic field and a non-specific hydrophobic binding site, pertaining to two catalytic aspects, namely thiolate anion stabilization and solvent shielding.
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- Thoren, S, et al.
(författare)
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Human microsomal prostaglandin E synthase-1: purification, functional characterization, and projection structure determination.
- 2003
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Ingår i: Journal of Biological Chemistry. - 1083-351X .- 0021-9258. ; 278:25, s. 209-22199
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Tidskriftsartikel (refereegranskat)abstract
- Human, microsomal, and glutathione-dependent prostaglandin (PG) E synthase-1 (mPGES-1) was expressed with a histidine tag in Escherichia coli. mPGES-1 was purified to apparent homogeneity from Triton X-100-solubilized bacterial extracts by a combination of hydroxyapatite and immobilized metal affinity chromatography. The purified enzyme displayed rapid glutathione-dependent conversion of PGH2 to PGE2 (Vmax; 170 µmol min–1 mg–1) and high kcat/Km (310 mM–1 s–1). Purified mPGES-1 also catalyzed glutathione-dependent conversion of PGG2 to 15-hydroperoxy-PGE2 (Vmax; 250 µmol min–1 mg–1). The formation of 15-hydroperoxy-PGE2 represents an alternative pathway for the synthesis of PGE2, which requires further investigation. Purified mPGES-1 also catalyzed glutathione-dependent peroxidase activity toward cumene hydroperoxide (0.17 µmol min–1 mg–1), 5-hydroperoxyeicosatetraenoic acid (0.043 µmol min–1 mg–1), and 15-hydroperoxy-PGE2 (0.04 µmol min–1 mg–1). In addition, purified mPGES-1 catalyzed slow but significant conjugation of 1-chloro-2,4-dinitrobenzene to glutathione (0.8 µmol min–1 mg–1). These activities likely represent the evolutionary relationship to microsomal glutathione transferases. Two-dimensional crystals of purified mPGES-1 were prepared, and the projection map determined by electron crystallography demonstrated that microsomal PGES-1 constitutes a trimer in the crystal, i.e. an organization similar to the microsomal glutathione transferase 1. Hydrodynamic studies of the mPGES-1-Triton X-100 complex demonstrated a sedimentation coefficient of 4.1 S, a partial specific volume of 0.891 cm3/g, and a Stokes radius of 5.09 nm corresponding to a calculated molecular weight of 215,000. This molecular weight, including bound Triton X-100 (2.8 g/g protein), is fully consistent with a trimeric organization of mPGES-1.
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- WEINANDER, R, et al.
(författare)
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Heterologous expression of rat liver microsomal glutathione transferase in simian COS cells and Escherichia coli
- 1995
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Ingår i: The Biochemical journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 311311 ( Pt 3), s. 861-866
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Tidskriftsartikel (refereegranskat)abstract
- The cDNA coding for rat liver microsomal glutathione transferase was subcloned into the mammalian expression vector pCMV-5 and the construct was transfected into, and transiently expressed in, simian COS cells. This resulted in high expression (0.7% of the microsomal protein). The activity towards 1-chloro-2,4-dinitrobenzene in microsomes was 15-30 nmol/min per mg, which increased upon N-ethylmaleimide treatment to 60-200 nmol/min per mg. Control and antisense-vector-treated cells displayed very low activity (3-6 nmol/min per mg). A DNA fragment coding for rat microsomal glutathione transferase was generated by PCR, cloned into the bacterial expression vector pSP19T7LT and transformed into Escherichia coli strain BL21 (DE3) (which contained the plasmid pLys SL). Isopropyl beta-D-thiogalactopyranoside (IPTG; 1 mM) induced the expression of significant amounts of enzymically active protein (4 mg/l of culture as measured by Western blots). The recombinant protein was purified and characterized and found to be indistinguishable from the rat liver enzyme with regard to enzymic activity, molecular mass and N-terminal amino acid sequence. Human liver cDNA was used to obtain the coding region of human microsomal glutathione transferase by PCR. This PCR product was cloned into pSP19T7LT, which, upon induction with IPTG, yielded significant amounts (9 mg/l of culture) of active enzyme in BL21 (DE3) cells. Thus, for the first time, it is now possible to express both human and rat microsomal glutathione transferase in an enzymically active form in Escherichia coli.
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