Members of the PhaF / MrpF family are predicted to be an integral membrane proteins with three transmembrane regions, involved in regulation of pH. PhaF is part of a potassium efflux system involved in pH regulation. It is also involved in symbiosis in Rhizobium meliloti [1]. MrpF is part of a Na+/H+ antiporter complex, also involved in pH homeostasis. MrpF is thought to be an efflux system for Na+ and cholate [2]. The Mrp system in Bacilli may also have primary energisation capacities [3].

1: The pha gene cluster of Rhizobium meliloti involved in pH adaptation and symbiosis encodes a novel type of K+ efflux system. Putnoky P, Kereszt A, Nakamura T, Endre G, Grosskopf E, Kiss P, Kondorosi A; Mol Microbiol 1998;28:1091-1101. PMID:9680201

2: mrp, a multigene, multifunctional locus in Bacillus subtilis with roles in resistance to cholate and to Na+ and in pH homeostasis. Ito M, Guffanti AA, Oudega B, Krulwich TA; J Bacteriol 1999;181:2394-2402. PMID:10198001

3: Mrp-dependent Na(+)/H(+) antiporters of Bacillus exhibit characteristics that are unanticipated for completely secondary active transporters. Ito M, Guffanti AA, Krulwich TA; FEBS Lett 2001;496:117-120. PMID:11356194