Description
The biological catalyst that reduces atmospheric N2
to ammonia is the metalloenzyme nitrogenase which exists in three genetically distinct forms: the conventional
Mo-based system, Mo-nitrogenase, and two more
recently discovered alternative systems, V-nitrogenase
and nitrogenase-3. As early as 1930 (81) molybdenum,
Mo, was believed to be absolutely essential for nitrogen
fixation, even though vanadium, V, was found to be almost
as stimulatory to bacterial growth on N2 (82). The requirement
for Mo was solidified both by the isolation of the
larger of the two component proteins of nitrogenase, the
molybdenum–iron, MoFe, protein (83) having a FeMocofactor
(84), and later by the discovery of nitrogen-fixation
specific (nif) genes involved in Mo-specific functions.
Agricultural Uses
The enzyme nitrogenase fixes inert nitrogen in soils. It
lowers the activation energy required for the conversion
of nitrogen (N) to ammonia (NH3 ).Nitrogen fixation by microorganisms
can be symbiotic and non-symbiotic.
The nitrogenase enzyme complex consists of two
proteins. The first is a larger molybdenum-iron protein of
2 to 2.7 x105 molecular weight, containing 1 or 2 atom
of molybdenum, 17 to 36 atoms of iron and 14 to 28 acid
labile sulphur atoms. The second is an iron-protein
molecule of 55 to 67 x 103 molecular weight, containing
four atoms each of iron and acid labile sulphur.
