H+, K+, and Na+ transport across phospholipid vesicular membrane by the combined action of proton uncoupler 2,4-dinitrophenol and valinomycin.
The decay of the pH difference (delta pH) 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 approximately 6 to pH approximately 8): (i) The rate limiting step in the proton transport cycle is not the transport of proton as DNPH, but the back transport 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 approximately 1.5 x 10(3) s-1. (ii) The dissociation constant of the ternary complex Val-M(+)-DNP- in the membrane are approximately 1 mM for M+ = K+ and approximately 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 delta pH decay rate should also be a strategy for the efficient uncoupling of oxidative and photophosphorylation.
Prabhananda
B S
BS
Chemical Physics Group, Tata Institute of Fundamental Research, Mumbai, India.
Kombrabail
M H
MH
D019297:2,4-Dinitrophenol; D001190:Arylsulfonates; D001692:Biological Transport / Q000187:drug effects; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004140:Dinitrophenols / Q000494:pharmacology*; D005456:Fluorescent Dyes; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D014475:Uncoupling Agents / Q000494:pharmacology*; D014634:Valinomycin / Q000494:pharmacology*
D001190:Arylsulfonates; D004140:Dinitrophenols; D005456:Fluorescent Dyes; D008081:Liposomes; D010743:Phospholipids; D014475:Uncoupling Agents; D014634:Valinomycin; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D006859:Hydrogen; D012964:Sodium; C005047:pyranine; D019297:2,4-Dinitrophenol; D011188:Potassium