title: Preliminary evidence on existence of transplasma membrane electron transport in Entamoeba histolytica trophozoites: a key mechanism for maintaining optimal redox balance.
abstract: Entamoeba histolytica, an amitochondriate parasitic protist, was demonstrated to be capable of reducing the oxidized form of alpha-lipoic acid, a non permeable electron acceptor outside the plasma membrane. This transmembrane reduction of non permeable electron acceptors with redox potentials ranging from -290 mV to +360 mV takes place at neutral pH. The transmembrane reduction of non permeable electron acceptors was not inhibited by mitochondrial electron transport inhibitors such as antimycin A, rotenone, cyanide and azide. However, a clear inhibition with complex III inhibitor, 2-(n-heptyl)-4-hydroxyquinoline-N-oxide; modifiers of sulphydryl groups and inhibitors of glycolysis was revealed. The iron-sulphur centre inhibitor thenoyltrifluoroacetone failed to inhibit the reduction of non permeable electron acceptors whereas capsaicin, an inhibitor of energy coupling NADH oxidase, showed substantial inhibition. p-trifluromethoxychlorophenylhydrazone, a protonophore uncoupler, resulted in the stimulation of alpha-lipoic acid reduction but inhibition in oxygen uptake. Mitochondrial electron transport inhibitors substantially inhibited the oxygen uptake in E. histolytica. Transmembrane reduction of alpha-lipoic acid was strongly stimulated by anaerobiosis and anaerobic stimulation was inhibited by 2-(n-heptyl)-4-hydroxyquinoline-N-oxide. Transmembrane redox system of E. histolytica was also found to be sensitive to UV irradiation. All these findings clearly demonstrate the existence of transplasma membrane electron transport system in E. histolytica and possible involvment of a naphthoquinone coenzyme in transmembrane redox of E. histolytica which is different from that of mammalian host and therefore can provide a novel target for future rational chemotherapeutic drug designing.
authors.affiliation: Department of Pharmaceutical Technology, Division of Medicinal Biochemistry, Jadavpur University, Kolkata, 700 032, West Bengal, India.
authors.forename: Tanmoy
authors.initials: T
authors.lastname: Bera
authors.forename: Nilay
authors.initials: N
authors.lastname: Nandi
authors.forename: D
authors.initials: D
authors.lastname: Sudhahar
authors.forename: Md Ali
authors.initials: MA
authors.lastname: Akbar
authors.forename: Abhik
authors.initials: A
authors.lastname: Sen
authors.forename: Pradeep
authors.initials: P
authors.lastname: Das
mesh_terms: D000693:Anaerobiosis; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D045222:Electron Transport Chain Complex Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004748:Entamoeba histolytica / Q000378:metabolism*; D005292:Ferricyanides / Q000378:metabolism; D006912:Hydroxyquinolines / Q000494:pharmacology; D007203:Indigo Carmine / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects / Q000528:radiation effects; D010100:Oxygen / Q000378:metabolism; D013804:Thenoyltrifluoroacetone / Q000494:pharmacology; D008063:Thioctic Acid / Q000378:metabolism; D053058:Trophozoites / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D045222:Electron Transport Chain Complex Proteins; D005292:Ferricyanides; D006912:Hydroxyquinolines; D008565:Membrane Proteins; C007931:hexacyanoferrate III; C001333:2-(n-heptyl)-4-hydroxyquinoline N-oxide; D013804:Thenoyltrifluoroacetone; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D008063:Thioctic Acid; D007203:Indigo Carmine; D007501:Iron; D002211:Capsaicin; D010100:Oxygen