Involved in the fermentation of L-phenylalanine via a Stickland reaction. Required for the activation of the (R)-phenyllactate dehydratase complex FldABC. Only in the oxidized state, FldI exhibits significant ATPase activity, which appears to be essential for unidirectional electron transfer. This protein is extremely sensitive towards oxygen. Binds 1 [4Fe-4S] cluster per dimer. Amino-acid degradation; L-phenylalanine degradation. Homodimer.