Involved in the fermentation of L-glutamate via the hydroxyglutarate pathway. HgdC (CompA) has a very low ATPase activity, whose the role is to activate dehydratase HgdA-HgdB complex and then maintain an appropriate redox state via an ATP-dependent electron transfer. The dehydratase requires only catalytic amounts of ATP and substoichiometric amounts of HgdC (CompA) to be functional. ATP + H2O = ADP + H(+) + phosphate Binds 1 [4Fe-4S] cluster per dimer. Inactivated by exposure to air within less than 15 minutes. Amino-acid degradation; L-glutamate degradation via hydroxyglutarate pathway; crotonoyl-CoA from L-glutamate: step 4/5. Homodimer. HgdC (CompA) seems to require NADH to be functional. Belongs to the HgdC family.