title: Hydroperoxides selectively inhibit human erythrocyte membrane enzymes.
abstract: Treatment of washed erythrocytes with tert-butyl hydroperoxide (0.5 mM, 10 min) inhibited basal Ca2+ + Mg2+-ATPase activity by 40% and calmodulin-stimulated activity by 54%. The inhibition was accompanied by the formation of methemoglobin and the aggregation of some membrane proteins into a high-molecular-weight polymer. Membranes, isolated from washed erythrocytes, showed a similar pattern of inhibition. Basal Ca2+ + Mg2+-ATPase activity was inhibited 50% at 10 min and 70% at 30 min while calmodulin-stimulated activity was inhibited 70% at 10 min and 84% at 30 min. Thiobarbituric acid-reactive products formed slowly during the first 10 min and then increased sharply between 10 and 30 min. The polymerization of membrane proteins was also observed during the tert-butyl hydroperoxide exposure. Inhibition of erythrocyte membrane enzymes was selective. The Na+ + K+-stimulated Mg2+ ATPase, like the Ca2+ + Mg2+-ATPase, was sensitive to membrane oxidation but the activities of Mg2+-ATPase and acetylcholinesterase were less inhibited by tert-butyl hydroperoxide. Acetylcholinterase was found to be very resistant to hydroperoxide treatment with less than 10% loss of activity. The effects of two other hyproperoxides on enzyme inhibition were studied also. Cumene hydroperoxide (0.5 mM) was found to be as potent as tert-butyl hydroperoxide but hydrogen peroxide at 10 mM did not produce thiobarbituric acid-reactive products or inhibit Ca2+ + Mg2+-ATPase activity until after 20 min. The selective effects of peroxides on these enzyme activities are discussed.
authors.affiliation: Department of Pediatrics, University of South Alabama College of Medicine, Mobile 36617.
authors.forename: R B
authors.initials: RB
authors.lastname: Moore
authors.forename: M L
authors.initials: ML
authors.lastname: Brummitt
authors.forename: V N
authors.initials: VN
authors.lastname: Mankad
mesh_terms: D000110:Acetylcholinesterase / Q000032:analysis; D001555:Benzene Derivatives / Q000494:pharmacology; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000201:enzymology*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D010545:Peroxides / Q000494:pharmacology*; D020122:tert-Butylhydroperoxide
chemical_list: D001555:Benzene Derivatives; D010545:Peroxides; D020122:tert-Butylhydroperoxide; D006861:Hydrogen Peroxide; D000110:Acetylcholinesterase; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; C007164:cumene hydroperoxide