Inactivation of the plasma membrane ATPase ofSchizosaccharomyces pombe by hydrogen peroxide and by the fenton reagent (Fe2+/H2O2): Nonradicalvs. Radical-induced oxidation

• Published in: Folia microbiologica 1998-08, Vol.43 (4), p.361-367
• Main Authors: Sigler, K., Gille, G., Vacata, V., Stadler, N., Höfer, M.
• Format: Article
• Language: English
• Subjects: Adenosine triphosphatase; ATP; Binding sites; Blockage; Catalase; Deactivation; Ferrous ions; Hydrogen peroxide; Inactivation; Iron; Mannitol; Membrane proteins; Membranes; Oxidation; Plasma membranes; Proteins; Radicals; Reagents; Scavengers
• ISSN: 0015-5632; 1874-9356
• DOI: 10.1007/BF02818574

In the absence of added Fe2+, the ATPase activity of isolatedSchizosaccharomyces pombe plasma membranes (5–7 μmolPi per mg protein per min) is moderately inhibited by H2O2 in a concentration-dependent manner. Sizable inactivation occurs only at 50–80 mmol/L H2O2. The process, probably a direct oxidative action of H2O2 on the enzyme, is not induced by the indigenous membrane-bound iron (19.3 nmol/mg membrane protein), is not affected by the radical scavengers mannitol and Tris, and involves a decrease of both theKm of the enzyme for ATP and theV of ATP splitting. On exposing the membranes to the Fenton reagent (50 μmol/L Fe2+ +20 mmol/L H2O2), which causes a fast production of HO− radicals, the ATPase is 50–60% inactivated and 90% of added Fe2+ is oxidized to Fe3+ within 1 min. The inactivation occurs only when Fe2+ is added before H2O2 and can thus bind to the membranes. The lack of effect of radical scavengers (mannitol, Tris) indicates that HO− radicals produced in the bulk phase play no role in inactivation. Blockage of the inactivation by the iron chelator deferrioxamine implies that the process requires the presence of Fe2+ ions bound to binding sites on the enzyme molecules. Added catalase, which competes with Fe2+ for H2O2, slows down the inactivation but in some cases increases its total extent, probably due to the formation of the superoxide radical that gives rise to delayed HO− production.