Nucleotide and divalent cation specificity of in vitro iron-molybdenum cofactor synthesis.

The nucleotide and divalent cation requirements of the in vitro iron-molybdenum cofactor (FeMo-co) synthesis system have been compared with those of substrate reduction by nitrogenase. The FeMo-co synthesis system specifically requires ATP, whereas both 1,N6-etheno-ATP and 2'-deoxy-ATP function in place of ATP in substrate reduction (M. F. Weston, S. Kotake, and L. C. Davis, Arch. Biochem. Biophys. 225:809-817, 1983). Mn2+, Ca2+, and Fe2+ substitute for Mg2+ to various extents in in vitro FeMo-co synthesis, whereas Ca2+ is ineffective in substrate reduction by nitrogenase. The observed differences in the nucleotide and divalent cation specificities suggest a role(s) for the nucleotide and divalent cation in in vitro FeMo-co synthesis that is distinct from their role(s) in substrate reduction.