title: A highly active microsomal glutathione transferase from frog (Xenopus laevis) liver that is not activated by N-ethylmaleimide.
abstract: Microsomal glutathione transferase has hitherto only been purified from mammalian species. N-ethylmaleimide and trypsin activation (discriminating features of this enzyme) has only been observed in microsomes from mammals. In this paper we describe the first isolation and characterization of a non-mammalian microsomal glutathione transferase from frog (Xenopus laevis) liver. This protein has a molecular weight similar to that of the mammalian enzyme (approximately 17 kDa), but cannot be activated by N-ethylmaleimide or trypsin. In fact the enzyme is rapidly inactivated by this sulfhydryl reagent and protease. It thus appears that N-ethylmaleimide activation is not an obligatory property of microsomal glutathione transferase. The frog liver microsomal glutathione transferase has one of the highest specific activities towards the second substrate 1-chloro-2,4-dinitrobenzene (CDNB) (200 mumol/min mg) obtained with any glutathione transferase and accounts for the high activity found in frog liver microsomes. The kcat/K(m) for glutathione and CDNB are 0.017 and 1.1 x 10(6) M-1 s-1, respectively. The enzyme also functions as a glutathione peroxidase (dilinoleoyl phosphatidylcholine hydroperoxide is reduced (5.2 mumol/min mg)). It is now evident that a highly active microsomal glutathione transferase, with a molecular weight similar to that of the mammalian enzymes also exists in a non-mammal species.
authors.affiliation: Institute of Environmental Medicine, Division of Biochemical Toxicology, Stockholm, Sweden.
authors.forename: T H
authors.initials: TH
authors.lastname: Sun
authors.forename: X
authors.initials: X
authors.lastname: Ling
authors.forename: B
authors.initials: B
authors.lastname: Persson
authors.forename: R
authors.initials: R
authors.lastname: Morgenstern
mesh_terms: D000818:Animals; D004137:Dinitrochlorobenzene; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D005260:Female; D005982:Glutathione Transferase / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008322:Mammals; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D008970:Molecular Weight; D013045:Species Specificity; D013379:Substrate Specificity; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology; D014982:Xenopus laevis / Q000378:metabolism*
chemical_list: D004137:Dinitrochlorobenzene; D004791:Enzyme Inhibitors; D013439:Sulfhydryl Reagents; D005982:Glutathione Transferase; D014357:Trypsin; D005033:Ethylmaleimide