| 1. |
- Danielson, U Helena, et al.
(author)
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Kinetic independence of the subunits of cytosolic glutathione transferase from the rat
- 1985
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In: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 231:2, s. 263-267
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Journal article (peer-reviewed)abstract
- The steady-state kinetics of the dimeric glutathione transferases deviate from Michaelis-Menten kinetics, but have hyperbolic binding isotherms for substrates and products of the enzymic reaction. The possibility of subunit interactions during catalysis as an explanation for the rate behaviour was investigated by use of rat isoenzymes composed of subunits 1, 2, 3 and 4, which have distinct substrate specificities. The kinetic parameter kcat./Km was determined with 1-chloro-2,4-dinitrobenzene, 4-hydroxyalk-2-enals, ethacrynic acid and trans-4-phenylbut-3-en-2-one as electrophilic substrates for six isoenzymes: rat glutathione transferases 1-1, 1-2, 2-2, 3-3, 3-4 and 4-4. It was found that the kcat./Km values for the heterodimeric transferases 1-2 and 3-4 could be predicted from the kcat./Km values of the corresponding homodimers. Likewise, the initial velocities determined with transferases 3-3, 3-4 and 4-4 at different degrees of saturation with glutathione and 1-chloro-2,4-dinitrobenzene demonstrated that the kinetic properties of the subunits are additive. These results show that the subunits of glutathione transferase are kinetically independent.
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| 2. |
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| 3. |
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| 4. |
- Ålin, Per, et al.
(author)
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Purification of major basic glutathione transferase isoenzymes from rat liver by use of affinity chromatography and fast protein liquid chromatofocusing
- 1985
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In: Analytical Biochemistry. - : Elsevier BV. - 0003-2697 .- 1096-0309. ; 146:2, s. 313-320
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Journal article (peer-reviewed)abstract
- Seven major isoenzymes of glutahione transferase with isoelectric points ranging from pH 6.9 to 10 were isolated from rat liver cytosol. The purification procedure included affinity chromatography on immobilized S-hexylglutathione followed by high-performance liquid chromatofocusing. Characteristics, such as physical properties, reactions with antibodies, specific activities with various substrates, kinetic constants, and sensivities to a set of inhibitors, are given for discrimination and identification of the different isoenzymes. The multiple forms of the enzyme correspond to glutathione transferases 1-1, 1-2, 2-2, 3-3, 3-4, and 4-4 in the recently introduced nomenclature [W. B. Jakoby et al. (1984) Biochem. Pharmacol. 33, 2539–2540]. A seventh form appears to be a heterodimeric protein composed of subunit 3 and an as yet unidentified subunit.
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