ON MECHANISM OF UNCOUPLING IN CHLOROPLASTS BY ION-PERMEABILITY INDUCING AGENTS

A general mechanism is presented for uncoupling of chloroplasts by compounds or combination of compounds which increase membrane permeability to both protons and alkali metal cations. Agents which supposedly increase the membrane permeability to protons only, such as 2,4‐dinitrophenol and carbonyl cyanide p‐trifluoromethoxy phenylhydrazone (FCCP) (at low concentrations), did not uncouple chloroplasts. Similarly, the antibiotics valinomycin, and nonactin and the synthetic compound LR6‐125, which apparently increase only the cation permeability of membranes, did not uncouple. However, combinations of dinitrophenol or of low concentrations of FCCP with anyone of the cation permeability inducing agents, led to full uncoupling of the chloroplasts. Studies on the passive permeability properties of the grana membrane, support the assumption that combinations of dinitrophenol or FCCP (at low concentrations), with valino‐mycin or nonactin or LR6‐125, increase the membrane permeability to both proton and cations. High concentrations of FCCP (10 μM) which alone uncoupled chloroplasts, also appeared to increase the permeability of the membrane to both protons and to cations, while low concentrations of FCCP, which did not uncouple alone, sufficed to increase the membrane permeability to protons. It is suggested that the uncoupling produced by the compounds used in this work is of the same type as that induced by the antibiotics, gramicidin and nigericin, both of which were suggested to increase the membrane permeability to both protons and cations. Copyright © 1969, Wiley Blackwell. All rights reserved