Open AccessChanges in membrane ionic conductance, but not changes in slip, can account for the non‐linear dependence of the electrochemical proton gradient upon the electron‐transport rate in chromatophores
Author(s) -
COTTON Nicholas P. J.,
CLARK Adam J.,
JACKSON J. Barry
Publication year - 1984
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1984.tb08269.x
Subject(s) - chemistry , conductance , absorbance , membrane , electrochemical gradient , ionic bonding , electron transport chain , analytical chemistry (journal) , ion , proton transport , electrochemistry , inorganic chemistry , electrode , chromatography , biochemistry , organic chemistry , physics , condensed matter physics
Decrease in the rate of cyclic electron transport ( J E ) measured from the absorbance changes associated with reaction centre bacteriochlorophyll led to a less than proportionate decrease in the membrane potential (ΔΨ) measured by electrochromism. In principle this result can be explained either by a ΔΨ‐dependent slip in the H + /e − coupling ratio ( n E ) or by a ΔΨ‐dependent change in the membrane ionic conductance. Simultaneous measurement of the membrane ionic current ( J DIS ) did not reveal any significant changes in the H + /e − ratio ( J DIS /J E ) and showed that conductance changes ( J DIS /ΔΨ) account quantitatively for the curved dependence of ΔΨ on J E . Simultaneous recordings of J DIS and the extravesicular pH from cresol‐red absorbance changes, suggest that protons are the main current‐carrying species across the chromatophore membrane at high values of ΔΨ in the presence and absence of F 0 ‐ATPase inhibitor. At reduced ΔΨ the flux of other ions outweighs the hydrogen ion current.