title: The effect of temperature and chronic ethanol feeding on the proton electrochemical potential and phosphate potential in rat liver mitochondria.
abstract: The relationship between the proton electrochemical potential (delta mu H) and the maximal free energy of ATP hydrolysis (delta GP) in coupled respiring rat liver mitochondria was investigated as a function of temperature and chronic ethanol-feeding. The flow dialysis method was utilized to measure the temperature dependence of delta mu H from the uptake of 86Rb (in the presence of valinomycin) and [14C]DMO. delta GP in state 4 was determined by a null-point titration of the reversible, H+-coupled ATPase against the phosphate potential. delta mu H increases with temperature from 196 mV at 10 degrees C, to 217 mV at 40 degrees C. The maximal delta GP at state 4 decreases as a function of temperature from 67.8 kJ/mol at 10 degrees C, to 54.8 kJ/mol at 40 degrees C. As a result, the ratio delta GP/delta mu H decreases with temperature from 3.56 at 10 degrees C to 2.60 at 40 degrees C. Similar studies with mitochondria from rats which were chronically fed with ethanol show that, while delta GP at state 4 decreases in these rats from 61.2 to 56.0 (25 degrees C), the delta mu H is essentially unchanged at 212 mV. Thus the ratio delta GP/delta mu H in ethanol-fed rats at 25 degrees C is 2.77 as compared with 2.97 in control. Similar reduction of delta GP was observed in inverted inner membranes from ethanol-fed rats. Both the temperature dependence of delta GP/delta mu H and the effect of ethanol-feeding cannot be easily explained by the chemiosmotic hypothesis which postulates that delta mu H is the only driving force for ATP synthesis. In contrast, a parallel coupling model, which postulates that intramembrane proton transfer from redox pumps to ATPase is mediated by the formation of dynamic aggregates of the mitochondrial inner-membrane proteins, can easily accommodate these findings. Accordingly, the temperature effect is due to weakening of these fragile aggregates, while the ethanol-feeding effect is the result of reduced concentration of active pumps, which decrease the frequency of formation of functional aggregates.
authors.forename: H
authors.initials: H
authors.lastname: Rottenberg
authors.forename: D E
authors.initials: DE
authors.lastname: Robertson
authors.forename: E
authors.initials: E
authors.lastname: Rubin
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D004579:Electron Transport / Q000187:drug effects; D000431:Ethanol / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D008930:Mitochondria, Liver / Q000187:drug effects*; D008954:Models, Biological; D010085:Oxidative Phosphorylation / Q000187:drug effects*; D006180:Proton-Translocating ATPases / Q000378:metabolism; D011522:Protons; D051381:Rats; D011919:Rats, Inbred Strains; D013696:Temperature; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D008565:Membrane Proteins; D011522:Protons; D014475:Uncoupling Agents; D000431:Ethanol; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases