Nitrogenase.pptx

PG AND RESEARCH DEPARTMENT OF MICROBIOLOGY,SRI PARAMAKALYANI COLLEGE, ALWARKURUCHI.

1. SRI PARAMAKALYANI COLLEGE Reaccredited with B Grade with a CGPA of 2.71 in the second cycle of NAAC affiliated to manonmanium sundaranar university, Tirunelveli. ALWARKURICHI – 627 412 Post graduate and Research Centre – Department of Microbiology (Government aided) ACADEMIC YEAR 2021 – 2022 I SEM CORE: PHYSIOLOGY AND METABOLISM UNIT IV NITROGENASE ENZYME SUBMITTED BY, K. RAMKUMAR REG NO: 20211232516122 I M.SC MICROBIOLOGY SUBMITTED TO GUIDE: DR.S.VISWANATHAN ASSISTANT PROFESSOR AND HEAD OF DEPARTMENT

2. Synopsis Introduction Classification Structure Nitrogenase Mechanism Organisms synthesize

3. Introduction Nitrogenase are enzymes, that are produced by certain bacteria (such as cyanobacteria and rhizobacteria ). These enzymes are responsible for the reduction of nitrogen (N 2 ) to ammonia (NH 3 ). Nitrogenases are the only family of enzymes known to catalyze this reaction, which is a key step in the process of  Nitrogen fi xation . Nitrogen fixation is required for all forms of life, with nitrogen being essential for the  biosynthesis  of  molecules   ( nucleotides ,  amino acids ) that create plants, animals and other organisms. They are encoded by the  Nif genes  or  homologs . They are related to  protochlorophyllide reductase .

4. Classification Molybdenum nitrogenase (Mo) Vanadium nitrogenase (V) Iron-only nitrogenase.

5. Structure Although the equilibrium of ammonia from molecular hydrogen and nitrogen has an overall negative enthalpy of reaction, the activation energy is very high. Nitrogenase acts as a catalyst. Consists of two components: I. The heterotetrameric MoFe protein, a nitrogenase which uses the electrons provided to reduce II. The homodimeric Fe-only protein, the reductase which has a high reducing power and is responsible for the the supply of electrons.

6. Structure:

7. Nitrogenase The MoFe protein is a heterotetramer consisting of two α subunits and two β subunits, with a mass of approximately 240-250kDa.  The MoFe protein also contains two  iron–sulfur clusters , known as P-clusters, located at the interface between the α and β subunits and two  FeMo cofactors , within the α subunits. The oxidation state of Mo in these nitrogenases was formerly thought Mo(V), but more recent evidence is for Mo(III).  Molybdenum in other enzymes is generally bound to  molybdopterin  as fully oxidized Mo(VI) . The core (Fe 8 S 7 ) of the P-cluster takes the form of two [Fe 4 S 3 ] cubes linked by a central carbon atom. Each P-cluster is  covalently  linked to the MoFe protein by six cysteine residues.

8. Each FeMo cofactor (Fe 7 MoS 9 C) consists of two non-identical clusters: [Fe 4 S 3 ] and [MoFe 3 S 3 ], which are linked by three sulfide ions. Each FeMo cofactor is covalently linked to the α subunit of the protein by one  cysteine  residue and one  histidine  residue. Electrons from the Fe protein enter the MoFe protein at the P-clusters, which then transfer the electrons to the FeMo cofactors. Each FeMo cofactor then acts as a site for nitrogen fixation, with N 2  binding in the central cavity of the cofactor.

9. Mechanism Nitrogenase is an enzyme responsible for catalyzing  nitrogen fixation , which is the reduction of nitrogen (N 2 ) to ammonia (NH 3 ) and a process vital to sustaining life on Earth.  There are three types of nitrogenase found in various nitrogen-fixing bacteria: molybdenum (Mo) nitrogenase,  vanadium (V) nitrogenase , and iron-only (Fe) nitrogenase.  Molybdenum nitrogenase, which can be found in  diazotrophs  such as  legume -associated  rhizobia , is the nitrogenase that has been studied the most extensively and thus is the most well characterized.  T he crystal structure and key catalytic components of molybdenum nitrogenase extracted from  Azotobacter vinelandii . Vanadium nitrogenase and iron-only nitrogenase can both be found in select species of Azotobacter as an alternative nitrogenase. 

10. Function :

11. Equations 1 and 2 show the balanced reactions of nitrogen fixation in molybdenum nitrogenase and vanadium nitrogenase respectively. N 2  + 14 H +  + 12 e −  + 40 MgATP → 2 NH 4 +  + 3 H 2  + 40 MgADP + 40 P i N 2  + 8 H +  + 8 e −  + 16 MgATP → 2 NH 3  + H 2  + 16 MgADP + 16 P i

12. All nitrogenases are two-component systems made up of Component I (also known as dinitrogenase ) and Component II (also known as dinitrogenase reductase). Component I is a MoFe protein in molybdenum nitrogenase, a VFe protein in vanadium nitrogenase, and a Fe protein in iron-only nitrogenase.  Component II is a Fe protein that contains the Fe-S cluster, which transfers electrons to Component I.  Component I contains 2 key metal clusters: the P-cluster, and the  FeMo -cofactor  ( FeMo -co) . Mo is replaced by V or Fe in vanadium nitrogenase and iron-only nitrogenase respectively.  During catalysis, electrons flow from a pair of ATP molecules within Component II to the Fe-S cluster, to the P-cluster, and finally to the FeMo -co, where reduction of N 2  to NH 3  takes place.

13. Picture :

14. Organisms synthesize Symbiotic bacteria – Example: Rhizobium, spirillum, Frankia Non symbiotic bacteria – Example: cyanobacteria, azotobacter, Green s bacteria.