On the Relationship between Rate of ATP Synthesis and H+ Electrochemical Gradient in Rat‐Liver Mitochondria

Abstract

The relationship between rate of ATP synthesis, JATP, and value of the proton electrochemical gradient, .DELTA.~.mu.H, was analyzed in intact mitochondria. Onset of phosphorylation causes a depression of .DELTA.~.mu.H of 1.5 kJ/mol. There is a close parallelism between inhibition of JATP and restoration of .DELTA.~.mu.H to its state-4 value during titrations with oligomycin or atractyloside. Titrations with ionophores display the following features: .DELTA.~.mu.H can be depressed by 3-4 kJ/mol by valinomycin + K+ without affecting the rate of ATP synthesis; uncouplers abolish JATP completely while depressing .DELTA.~.mu.H by 3 kJ/mol; complete abolition of ATP synthesis by inhibitors of electron transport is accompanied by a depression of .DELTA.~.mu.H of only 1 kJ/mol. There is a close functional relationship between redox and ATPase H+ pumps, whereby inhibition of electron transfer is accompanied by simultaneous inhibition of the ATPase H+ pumps and uncoupling of oxidative phosphorylation is not due to depression of .DELTA.~.mu.H per se. The consistence of the present data with either a chemiosmotic model where .DELTA.~.mu.H is the sole and obligatory intermediate for energy coupling, or models where there is a direct transfer of energy between the 2 pumps is discussed.