ABSTRACT
The import and export of ions and metabolites across cellular and organelle membranes are now understood in terms of Peter Mitchell’s chemiosmotic theory. In its broad outlines the latter states that the translocations across the essentially impermeable barrier of the lipid bilayer are accomplished by proteins that span the membrane and function as transducers of chemical, osmotic, and electrical free energy. Experimental systems for exploring these bioenergetic processes in bacteria include intact cells and cell-free systems prepared from them. In the case of the halobacteria, the intact cells are active in transport and adenosine triphosphate (ATP) synthesis, and have been used in penetrating studies of these two activities, both before and after depletion of their internal substrates by starvation. The conversion of arginine to citrulline by a desaminase in the halobacteria is followed by the production of ornithine and carbamoyl phosphate.
