β-Citryl-L-glutamate Acts as an Iron Carrier to Activate Aconitase Activity

Abstract

The compound β-citryl-L-glutamate (β-CG) was initially isolated from developing brains, though its functional roles remain unclear. In in vitro experiments, the [Fe(II)(β-CG)] complex activated aconitase in the presence of reducing reagents, whereas no Fe complex with citrate, glutamate, or deferoxamine displayed such an effect. β-CG and [Fe(II)(β-CG)] both bound to the fourth labile Fe atom (Fe_a) in the [4Fe–4S] cluster of aconitase. Furthermore, [Fe(II)(β-CG)] reactivated aconitase damaged by ammonium peroxodisulfate (APS), while β-CG and citrate had no effect. These findings suggest that [Fe(II)(β-CG)] can transfer Fe to aconitase disassembled by APS. In intact mitochondria, both β-CG and [Fe(II)(β-CG)] bound to Fe_a of aconitase, whereas only [Fe(II)(β-CG)] reactivated the enzyme disassembled by APS. In cultured neuronal cells, β-CG significantly enhanced cell viability by accelerating mitochondrial activity in primary cultures of neurons from newborn mouse cerebrum tissues. Thus, the β-CG plays a role as an Fe-carrier for mitochondrial aconitase, and then activates it. Taken together, these findings suggest that β-CG is an endogenous low molecular weight Fe chaperone for aconitase.