title: Exogenous energy supply to the plasma membrane of dark anaerobic cyanobacterium Anacystis nidulans: thermodynamic and kinetic characterization of the ATP synthesis effected by an artificial proton motive force.
abstract: The net synthesis of ATP in dark anaerobic cells of Anacystis nidulans subjected to acid jumps and/or valinomycin pulses was characterized thermodynamically and kinetically. Maximum initial rates of 75 nmol ATP/min per mg dry weight at an applied proton motive force of -350 mV were obtained, the flow-force relationship (rate of ATP synthesis vs applied proton motive force) being linear between -240 and -320 mV irrespective of the source of the proton motive force. The pulse-induced ATP synthesis was inhibited by uncouplers (H+ ionophores) and F0F1-ATPase inhibitors but not by KCN or CO. In order to obtain maximum rates of pulse-induced ATP synthesis both a favorable stationary delta psi (-100 mV at pHo 9, preceding the acid jumps) and a favorable stationary delta pH (+2 units at pHo 4.1, preceding the valinomycin pulse) of the plasma membrane were obligatory, the effects of delta psi and delta pH being strictly additive. Moreover, the pulse-induced ATP synthesis required a minimum total proton motive force of -200 to -250 mV across the plasma membrane; it also required low preexisting phosphorylation potentials corresponding to -400 mV in dark anaerobic, i.e., energy-depleted, cells. The results are discussed in terms of both a reversible H+-ATPase and a respiratory electron transport system occurring in the plasma membrane of intact Anacystis nidulans.
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D000693:Anaerobiosis; D002462:Cell Membrane / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism*; D003624:Darkness; D004734:Energy Metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008564:Membrane Potentials; D011522:Protons; D013816:Thermodynamics; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D000227:Adenine Nucleotides; D011522:Protons; D014634:Valinomycin; D000255:Adenosine Triphosphate