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- Andersson, C, et al.
(författare)
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Activation and inhibition of microsomal glutathione transferase from mouse liver.
- 1988
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Ingår i: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 249:3, s. 819-23
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Tidskriftsartikel (refereegranskat)abstract
- Mouse liver microsomal glutathione transferase was purified in an N-ethylmaleimide-activated as well as an unactivated form. The enzyme had a molecular mass of 17 kDa and a pI of 8.8. It showed cross-reactivity with antibodies raised against rat liver microsomal glutathione transferase, but not with any of the available antisera raised against cytosolic glutathione transferases. The fully N-ethylmaleimide-activated enzyme could be further activated 1.5-fold by inclusion of 1 microM-bromosulphophthalein in the assay system. The latter effect was reversible, which was not the case for the N-ethylmaleimide activation. At 20 microM-bromosulphophthalein the activated microsomal glutathione transferase was strongly inhibited, while the unactivated form was activated 2.5-fold. Inhibitors of the microsomal glutathione transferase from mouse liver showed either about the same I50 values for the activated and the unactivated form of the enzyme, or significantly lower I50 values for the activated form compared with the unactivated form. The low I50 values and the steep slope of the activity-versus-inhibitor-concentration curves for the latter group of inhibitors tested on the activated enzyme indicate a co-operative effect involving conversion of activated enzyme into the unactivated form, as well as conventional inhibition of the enzyme.
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| 2. |
- Söderström, Mats, et al.
(författare)
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Leukotriene C synthase in mouse mastocytoma cells. An enzyme distinct from cytosolic and microsomal glutathione transferases
- 1988
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Ingår i: Biochemical Journal. - : Portland Press. - 0264-6021 .- 1470-8728. ; 250:3, s. 713-718
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Tidskriftsartikel (refereegranskat)abstract
- Leukotriene C4 synthesis was studied in preparations from mouse mastocytoma cells. Enzymic conjugation of leukotriene A4 with glutathione was catalysed by both the cytosol and the microsomal fraction. The specific activity of the microsomal fraction (7.8 nmol/min per mg of protein) was 17 times that of the cytosol fraction. The cytosol fraction of the mastocytoma cells contained two glutathione transferases, which were purified to homogeneity and characterized. A microsomal glutathione transferase was purified from mouse liver; this enzyme was shown by immunoblot analysis to be present in the mastocytoma microsomal fraction at a concentration one-tenth or less of that in the liver microsomal fraction. Both the cytosolic and the microsomal glutathione transferases in the mastocytoma cells were identified with enzymes previously characterized, by determining specific activities with various substrates, sensitivities to inhibitors, reactions with antibodies, and physical properties. The purified microsomal glutathione transferase from liver was inactive with leukotriene A4 or its methyl ester as substrate. The cytosolic enzymes displayed activity with leukotriene A4, but their specific activities and intracellular concentrations were too low to account for the leukotriene C4 formation in the mastocytoma cells. The microsomal fraction of the cells contained an enzyme distinguishable by various criteria from the previously studied glutathione transferases. This membrane-bound enzyme, leukotriene C synthase (leukotriene A4:glutathione S-leukotrienyltransferase), appears to carry the main responsibility for the biosynthesis of leukotriene C4.
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