Nitrogenase enzyme is crucial for nitrogen fixation, found in bacteria associated with plant roots like legumes, consisting of large and small protein subunits that require Mg2+ ions for activation. Nif genes are responsible for regulating nitrogen fixation in Klebsiella pneumoniae, comprising 17 genes organized into operons that encode various functions related to the synthesis and processing of the nitrogenase components. Gene expression is regulated by external and internal systems, with the ntr system activating nif genes in response to nitrogen starvation.

1. NITROGENASE ENZYME
LUTOMIA R. DESMOND
MSC IN MICROBIOLOGY
MAHARISHI MARKANDESHWAR UNIVERSITY

2. Nitrogenase enzyme complex
Enzyme that facilitates fixation of nitrogen.
Found in nitrogen fixing bacteria that live in the
roots of plants such as legumes.
Structure:
Made up of two subunits mainly called; larger
MoFe protein (220,000 dalton mol. wt) and
another smaller Fe protein (55,000 dalton
mol.wt).
They need Mg2+ ions for activation.
Converts ATP to ADP during functioning.

4. Regulation of N2 Fixation in Klebsiella pneumoniae by Nif genes
Nif genes are the nitrogen fixation genes.
Organized into regulons of 17 genes consisting of
7 operons each of which is transcribed into a
single, usually polycistronic mRNA.

6. Functions of different Nif genes
Genes K and D encodes for the synthesis of
MoFe protein and H encodes for the synthesis of
Fe protein.
F and J participate in the transfer of electrons to
the Nase subunit of the Nitrogenase enzyme.
N, E and B participate in the synthesis and
processing of Fe-Mo cofactor.
M participates in the processing of the Fe-protein
subunits which are the products of gene H.
S and V are involved in the processing of Mo-Fe
protein subunits.

7.  V influences the specificity of Mo-Fe Protein
subunits.
 A and L are regulatory genes
 A activates the transcription of other genes.
 L represses the transcription of other genes.
 X and Y are found in the gene map of Nif gene
cluster but the functions are not yet known.
 Q participate in the uptake of Mo during the
synthesis of Nase

8. Regulation of Nif gene
 Regulation of Nif gene expression has an external system
designated Ntr and an internal system mediated by NifA and
NifL.
 The Nitr system responds to nitrogen starvation by activating
genes that utilize amino acids as nitrogen source switching on
the Nif genes.
 NtrA is a factor of RNA polymerase which recognizes the Nif
and other regulated genes.
 NtrA allows RNA polymerase to bind at Nif promoter
initiating transcription.