title: Zinc ions selectively inhibit steps associated with binding and release of NADP(H) during turnover of proton-translocating transhydrogenase.
abstract: Transhydrogenase couples the redox reaction between NAD(H) and NADP(H) to proton translocation across a membrane. In membrane vesicles from Escherichia coli and Rhodospirillum rubrum, the transhydrogenase reaction (measured in the direction driving inward proton translocation) was inhibited by Zn(2+) and Cd(2+). However, depending on pH, the metal ions either had no effect on, or stimulated, "cyclic" transhydrogenation. They must, therefore, interfere specifically with steps involving binding/release of NADP(+)/NADPH: the steps thought to be associated with proton translocation. It is suggested that Zn(2+) and Cd(2+) bind in the proton-transfer pathway and block inter-conversion of states responsible for changing NADP(+)/NADPH binding energy.
authors.affiliation: School of Biosciences, University of Birmingham, Edgbaston, UK.
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Whitehead
authors.forename: Karen E
authors.initials: KE
authors.lastname: Rossington
authors.forename: Abdul
authors.initials: A
authors.lastname: Hafiz
authors.forename: Nick P J
authors.initials: NP
authors.lastname: Cotton
authors.forename: J Baz
authors.initials: JB
authors.lastname: Jackson
mesh_terms: D017136:Ion Transport; D009249:NADP / Q000378:metabolism*; D009250:NADP Transhydrogenases / Q000378:metabolism*; D011485:Protein Binding; D011522:Protons; D015032:Zinc / Q000378:metabolism*
chemical_list: D011522:Protons; D009249:NADP; D009250:NADP Transhydrogenases; D015032:Zinc