J. Biol. Chem., Vol. 259, Issue 20, 12444-12448, Oct, 1984
Distinctions between the multiple cationic forms of rat liver glutathione S-transferase
H Maruyama, IM Arias and I Listowsky
Three cationic glutathione S-transferase forms isolated from rat liver were
characterized as dimers that originated from different combinations of two
subunit types, Ya and Yc. The cationic forms were purified using lysyl
glutathione affinity matrices and were chromatographically resolved from
anionic glutathione S-transferases that contain Yb subunits. The three
classes of cationic transferase exhibited similar specific activities with
1-chloro-2,4-dinitrobenzene as a substrate, all forms cross-reacted with
antibodies to glutathione S-transferase B, and all had comparable secondary
structures and tryptophan fluorescence properties. In spite of those
similarities, the Yc-containing forms were clearly distinguishable from Ya
forms on the basis of characteristic differences in circular dichroic
patterns associated with their aromatic side chains. All cationic
transferases bound bilirubin with stoichiometric ratios of 1 mol/dimeric
protein molecule, but discrete differences in mode of binding were ascribed
to forms containing Ya subunits as compared to Yc dimers. Binding to Yc
forms was of lower affinity and may be associated with the catalytic region
of the protein since glutathione effectively displaced bilirubin from the
Yc component.
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