H~+, K~+, and Na~+ transport across phospholipid vesicular membrane by the combined action of proton uncoupler 2,4-dinitrophenol and valinomycin

摘要

The decay of the pH difference (ΔpH) across soyabean phospholipid vesicular membrane (created by temperature jump), by the combined action of valinomycin and 2,4-dinitrophenol (DNP) has been monitored with the help of fluorescence from pyranine entrapped inside the vesicles under a variety of concentration conditions. The results suggest the following for the pH region of our interest (pH 6 to pH 8): (i) The rate limiting step in the proton transport cycle is not the transport of proton as DNPH, but the back transpsort of DNP? and the alkali metal ion M+ as Val-M+-DNP? across the membrane. The rate constant associated with the transport of the ternary complex has been estimated to be 1.5 · 103 s?1. (ii) The dissociation constant of the ternary complex Val-M+-DNP? in the membrane are 1 mM for M+=K+ and 0.001 mM for M+=Na+. (iii) The reduction in the cation selectivity of valinomycin on complexing with DNP? is much more than that observed with the anionic form of carbonyl cyanide m-chlorophenylhydrazone (CCCP). The results also provide a verification of a corollary of Mitchell's hypothesis: an experimental strategy which enhances the ΔpH decay rate should also be a strategy for the efficient uncoupling of oxidative and photophosphorylation.