Coupling between H⁺Entry and ATP Synthesis in Bacteria

This chapter focuses on the coupling between proton movements and the synthesis of ATP, a reaction catalyzed by the protontranslocating ATPase of bacteria. It discusses that in some cells, such as the streptococci, the ATPase normally couples ATP hydrolysis to the extrusion of protons, establishing both the membrane potential and pH gradient needed for other work functions. In all the experiments, the strategy examines the coupling between proton entry and ATP formation when an electrochemical proton gradient is artificially imposed, for in this way the effects of membrane potentials and pH gradients of known size are studied directly. For several reasons, it has been done using intact cells of Streptococcus lactis, an anaerobe. Such cells are easily depleted of metabolizable reserves, and in washed cells, the electrochemical proton gradient falls to nearly zero. In addition, this gram-positive organism is sensitive to ionophores without special pretreatment, so that the size of the membrane potential is manipulated by varying the ratio of internal to external potassium in the presence of the ionophore valinomycin. Finally, internal buffering power of the intact cell is high, so that net proton fluxes are readily observed in response to applied electrical or chemical gradients.