Local protons and uncoupling of aerobic and artificial delta muH-driven ATP synthesis.
Gramicidin D causes inhibition of ATP synthesis either in the absence or in the presence of depression of delta muH, in low-salt and in high-salt media, respectively, at concentrations 2 orders of magnitude higher in the former with respect to the latter case. When the number of active redox pumps is reduced by increasing the antimycin concentration, the P/O ratio of respiring, gramicidin-treated mitochondria either is slightly increased in low-salt media or is first decreased and then constant in high-salt media. Addition of gramicidin D in low-salt media to mitochondria synthesizing ATP by means of artificially imposed delta muH gradients results in (a) no effect on the K+ efflux ratio +/- ADP (equivalent to the aerobic respiratory control ratio) and (b) no effect on the ATP/K+ ratio (equivalent to the P/O ratio) except at the low gramicidin D concentrations where there is also a slight enhancement of the rate of ATP hydrolysis. During respiration-driven ATP synthesis, addition of valinomycin plus K+ causes depression of delta muH with little inhibition of ATP synthesis while addition of gramicidin D causes inhibition of ATP synthesis with little depression of delta muH. The view is discussed that the gramicidin-accessible protons which uncouple aerobic ATP synthesis in a delta muH-independent manner are of a different class from the gramicidin-inaccessible protons which uncouple diffusion potential driven ATP synthesis in a delta muH-dependent manner. The gramicidin-accessible protons are suggested to be pump associated and to reflect primary events in energy transduction.
Luvisetto
S
S
CNR Unit for the Study of the Physiology of Mitochondria, University of Padova, Italy.
Azzone
G F
GF
D000255:Adenosine Triphosphate / Q000096:biosynthesis* / Q000378:metabolism; D000332:Aerobiosis; D000818:Animals; D006096:Gramicidin / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D008962:Models, Theoretical; D010085:Oxidative Phosphorylation / Q000187:drug effects*; D010101:Oxygen Consumption / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D011522:Protons; D051381:Rats
D011522:Protons; D006096:Gramicidin; D000255:Adenosine Triphosphate; D011188:Potassium