While it is well known that all cells depend on metabolic energy to accumulate various nutrients, hardly anything is known about the energy coupling mechanism. To elucidate the coupling mechanism at the molecular level it is necessary to identify and characterize the relevant membrane components, especially the protein components. For this purpose we are using a simple homofermentative microbe, Streptococcus faecalis as a model system. There is considerable evidence that the membrane ATPase in the organism is involved in the energized transport of K plus ions and amino acids. The major objective of the project is to fully characterize the ATPase and the membrane proteins with which the enzyme is associated. Recently, we have discovered that the ATPase contains tightly bound forms of ATP and ADP. We will attempt to elucidate the functional significance of these nucleotide ligands in the enzyme.