Interaction of bacterial glutathione transferase with hemin.

Glutathione transferases (GSTs, EC 2.5.1.18) are pivotal enzymes for detoxification processes in eukaryotes and prokaryotes (1, 2). GSTs catalyse glutathione conjugation to a broad spectrum of compounds. In addition, functions not related to detoxification have been discovered for GSTs including steroid biosynthesis, signal transduction and intracellular transport (1). Hemin has been shown to be hazardous to the cell membrane because it inserts into the lipid bilayer and binds to membrane proteins. These interactions may cause membrane changes, which may lead to cellular lysis. The ability of several eukaryotic GSTs from pluricellular and unicellular organisms to interact with hemin has been widely investigated (3, 4), and this compound was shown to bind the enzyme with high affinity (3, 4). To verify if this interaction is a prerogative of eukaryotic GSTs or it has a general significance, we studied the binding of hemin to Proteus mirabilis GST (PmGST), a representative bacterial GST belonging to the Beta class. The interaction was studied by means of inhibition assays and fluorescence spectroscopy. Results obtained indicate that PmGST binds hemin efficiently, with a considerable quenching of the intrinsic fluorescence of PmGST. Furthermore, hemin was found to be a strong inhibitor of GST conjugation activity.