Accumulation of 99Mo-containing iron-molybdenum cofactor precursors of nitrogenase on NifNE, NifH, and NifX of Azotobacter vinelandii.

The biosynthesis of the iron-molybdenum cofactor (FeMo-co) of nitrogenase was investigated using the purified in vitro FeMo-co synthesis system and 99Mo. The purified system involves the addition of all components that are known to be required for FeMo-co synthesis in their purified forms. Here, we report the accumulation of a 99Mo-containing FeMo-co precursor on NifNE. Apart from NifNE, NifH and NifX also accumulate 99Mo label. We present evidence that suggests NifH may serve as the entry point for molybdenum incorporation into the FeMo-co biosynthetic pathway. We also present evidence suggesting a role for NifX in specifying the organic acid moiety of FeMo-co.