Application for Organic Nitrogen compounds - Nitrogenase

 

N2 + 8 H+ + 8 e- + 16 ATP + 16 H2O à 2 NH3 + 16 ADP + 16 Pi + H2 + 16 H+

 

Structure of Nitrogenase:

[Fe]-protein (60 kDa)  +  a2b2  [MoFe] protein (each subunit 60 kDa)

 

• The folding of the enzyme nitrogenase is due to its primary, secondary, tertiary and quartenary structure.
• a-helix and b-pleated sheets can be observed from the picture shown above.
• Other forces of attraction are also involved in stabilising the tertiary structure, eg. electrostatic forces between charged groups and hydrogen bonding between polar groups.
• Each of the polypeptide subunit adopts a tertiary structure to give the characteristics of the protein.

 

Nitrogenases have two component proteins:

• Fe-protein: functions as the e- donor; is a dimeric protein with a M.W. ~ 60 kDa. Has a [4Fe-4S] cluster which 1st receives e-, stores them and finally donates them to the site where N2 is reduced.
• Fe-Mo protein (in cases it is a Fe-only or Fe-V protein): A Fe-Mo cofactor of this protein is the actual site where N2 binds and is reduced.
• A P cluster within this protein is believed to be involved in e- transfer from the reduced [4Fe-4S] cluster of the Fe protein to the Fe-Mo cofactor.

Nitrogenase is the enzyme involved in some organisms to fix atmospheric nitrogen gas. As the N≡N triple bond is very high in energy, dinitrogen is quite inert. With the Fe-Mo cofactor, formation of multiple Fe-N interactions weakens the N≡N triple bond and lowers the activation energy barrier for the reduction. This can generate ammonia gas which is required by fertillisers.

 

Related process that produces ammonia gas from the reaction of nitrogen gas and hydrogen gas is the Haber process.