FIGURE 5.
Preliminary model of ACS activation by AcsFCh. ApoACS (1), which contains the [4Fe4S] cluster, but no nickel, can form a complex with either one dimer or two monomers of AcsFCh. The apoACS-AcsFCh complex (2) is then able to bind two nickel ions. The nickel ions may bind either sequentially (3) or simultaneously. However, neither the details of the nickel binding mechanism nor the location of the nickel binding site are known. ATP hydrolysis by AcsFCh converts inactive (4) to active ACS (5).