May catalyze the NADPH oxidation in the SfrAB NADPH-Fe(3+) oxidoreductase enzymatic complex. Probably involved in acetate metabolism and not in the reduction of Fe(3+) chelates. May serve as a major route for NADP regeneration. Binds 1 [4Fe-4S] cluster. Heterotetramer with 2 alpha subunits. PubMed:17906154 suggests that SfrAB is involved in acetate metabolism and does not participate directly in the reduction of Fe(3+) chelates, as was initially proposed in PubMed:11443080.