ATP binding by an FF ATP synthase ε subunit is pH dependent, suggesting a diversity of ε subunit functional regulation in bacteria.

It is a conjecture that the ε subunit regulates ATP hydrolytic function of the FF ATP synthase in bacteria. This has been proposed by the ε subunit taking an extended conformation, with a terminal helix probing into the central architecture of the hexameric catalytic domain, preventing ATP hydrolysis. The ε subunit takes a contracted conformation when bound to ATP, thus would not interfere with catalysis.