Exchange of organelle ATP with cytosolic ADP through the ADP/ATP carrier is
a well-characterized feature of mitochondrial metabolism. Obligate intrace
llular bacteria, such as Rickettsia prowazekii, and higher-plant plastids p
ossess another type of adenylate transporter, which exchanges bacterial or
plastidic ADP for ATP from the eukaryotic (host cell) cytoplasm. The bacter
ial and plastidic transporters are similar but do not share significant seq
uence similarities with the mitochondrial carrier. Recent molecular and bio
chemical studies are providing deeper insight into the functional and evolu
tionary relationships between the bacterial and the plant transport protein
s.