Zinc ions selectively inhibit steps associated with binding and release of NADP(H) during turnover of proton-translocating transhydrogenase.
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.
Whitehead
Simon J
SJ
School of Biosciences, University of Birmingham, Edgbaston, UK.
Rossington
Karen E
KE
Hafiz
Abdul
A
Cotton
Nick P J
NP
Jackson
J Baz
JB
D017136:Ion Transport; D009249:NADP / Q000378:metabolism*; D009250:NADP Transhydrogenases / Q000378:metabolism*; D011485:Protein Binding; D011522:Protons; D015032:Zinc / Q000378:metabolism*
D011522:Protons; D009249:NADP; D009250:NADP Transhydrogenases; D015032:Zinc