Properties and utility of the peculiar mixed disulfide in the bacterial glutathione transferase B1-1

Biochemistry
A M CaccuriG Ricci

Abstract

Bacterial glutathione transferases appear to represent an evolutionary link between the thiol:disulfide oxidoreductase and glutathione transferase superfamilies. In particular, the observation of a mixed disulfide in the active site of Proteus mirabilis glutathione transferase B1-1 is a feature that links the two families. This peculiar mixed disulfide between Cys10 and one GSH molecule has been studied by means of ESR spectroscopy, stopped-flow kinetic analysis, radiochemistry, and site-directed mutagenesis. This disulfide can be reduced by dithiothreitol but even a thousand molar excess of GSH is poorly effective due to an unfavorable equilibrium constant of the redox reaction (K(eq) = 2 x 10(-4)). Although Cys10 is partially buried in the crystal structure, in solution it reacts with several thiol reagents at a higher or comparable rate than that shown by the free cysteine. Kinetics of the reaction of Cys10 with 4,4'-dithiodipyridine at variable pH values is consistent with a pK(a) of 8.0 +/- 0.1 for this residue, a value about 1 unit lower than that of the free cysteine. The 4,4'-dithiodipyridine-modified enzyme reacts with GSH in a two-step mechanism involving a fast precomplex formation, followed by a slower chemical step...Continue Reading

References

Jan 1, 1997·Chemical Research in Toxicology·R N Armstrong
Apr 28, 2000·The Journal of Biological Chemistry·P G BoardJ Pandit
May 1, 1959·Archives of Biochemistry and Biophysics·G L ELLMAN

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Citations

Nov 20, 2008·The FEBS Journal·Nerino AllocatiCarmine Di Ilio
Jun 3, 2004·The Journal of Biological Chemistry·Giorgio RicciAnna Maria Caccuri

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