Purification of a GSH-affinity binding protein from Bacteroides fragilis devoid of glutathione transferase activity

An affinity binding protein from the cytosolic fraction of Bacteroides fragilis was purified by using epoxy activated-Sepharose 6B resin immobilized with GSH or with hexyl-GSH. This protein showed a subunit molecular mass (22 kDa) similar to that of glutathione transferase purified from Proteus mirabilis (22.5 kDa). However, the affinity binding protein of Bacteroides fragilis, unlike the GSH-affinity binding protein of Proteus mirabilis, was devoid of the capacity to conjugate GSH to the most commonly used glutathione transferase substrates. The GSH-affinity binding protein of Bacteroides fragilis was also antigenically different from the GSH-affinity bound protein of Proteus mirabilis. It was concluded that the anaerobic microorganism is not able to express glutathione transferase even though it contains a GSH-affinity binding protein with a structural characteristic reminiscent of aerobic glutathione transferase.