This family consists of several Rhizobium FixH like proteins. It has been suggested that suggested that the four proteins FixG, FixH, FixI, and FixS may participate in a membrane-bound complex coupling the FixI cation pump with a redox process catalysed by FixG [1].

1: Rhizobium meliloti fixGHI sequence predicts involvement of a specific cation pump in symbiotic nitrogen fixation. Kahn D, David M, Domergue O, Daveran ML, Ghai J, Hirsch PR, Batut J; J Bacteriol 1989;171:929-939. PMID:2536685