Structure and evolutionary relationships of F- and V-type ATPases. Orthologous subunits are shown by the same color and shape, and unrelated but functionally analogous subunits of the central stalk are shown by different colors and shapes. The subunits that show structural analogy but might not be homologous are shown by different but similar colors. The minimal, prokaryotic sets of subunits are depicted both for the F- and V-type ATPases. In the case of those V-ATPase subunits that are denoted by different letters in prokaryotes and eukaryotes, double notation is used: eukaryotic/prokaryotic. For further details, see ref. .