Microbiology Procedure

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Nitrogen Fixation Nitrogen Fixation Part 1 Structure of Nitrogenase Components Fe Protein Mo-Fe Protein Mechanism of Nitrogenase Action Hydrogen Evolution Factors Affecting Nitrogenase Activity Nitrogen Fixation Genes Nitrification Nitrate Formation - Nitrobacteria Nitrate Reduction Glutamate Synthase Pathway

Fe Protein

	Fe Protein - The Fe protein contains 4 iron and 4 acid labile sulphur atoms. It is a dimer of MW ranging from 57,674 (Clostridium pasteurianum) to 73,000 (Corynebacterium sp). In c.pasteurianum, the two subunits of the Fe protein are identical. The dimer contains one Fe₄S₄^* cluster. All Fe proteins isolated are dimers with 4 Fe atoms. It is likely that two cysteine thiols from each subunit are liganded to the Fe₄S^₄ center. The Fe protein from all organisms examined has (i) MW from 57,000 to 73,000, (ii) 4 iron atoms and 4 labile sulphur atoms (S) (iii) Two identical subunits and extreme sensitivity to oxygen (half life in air is approx. 30 sec.) The amino acid sequence of the Fe protein from Clostridium pasteurianum has been determined. The Fe protein consists of two identical monomers each with 273 amino acid residues. The cysteine residues are in positions 37, 82, 94, 129, 181, and 231 from the NH₂ end in each peptide (monomer).
The Fe₄S^₄ cluster is apparently liganded to two cysteine thiols of each peptide. Other arrangements may, however be possible. The Fe protein does not show any sequence homology with any other iron-sulphur protein.. It has the highest content of Gly-Gly (1139 residues) amongst all proteins examined. Four of the Gly-Gly sequences are predicted to form β-bends. The Fe protein contains several dipeptide and tripeptide sequences. It is noteworthy for the lack of tryptophan. There is an overall negative charge at neutral pH. The isoelectric point is about 4.4. The protein contains eight regions with 5 or more hydrophobic residues. The reduced protein undergoes different types of conformational changes on binding to Mg ATP and Mg ADP. The protein is designed to be flexible. The Fe₄S^₄ cluster can exist in four possible oxidation states (X)^-4, (X)^-3, (X)^-2, and X^-1, where (X) = [Fe₄S^*₄(Cys)₄]. The Fe protein supplies electrons one at a time to the Mo-Fe protein.
This transfer takes place when the Fe protein is complexed with Mg ATP-. The Fe protein, like the 4Fe and 8Fe ferredoxins, operates between the (X)^-2 and (X)^-3 states. The Fe protein has a midpoint potential (Em) of -250 to -295 m V in the absence of Mg ATP- . When complexed with 2Mg ATP-- the Em is about -400m V. Binding of Mg ATP- - to the Fe protein increases its oxygen sensitivity. The binding of Mg ADP is greater than that of Mg ATP.

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Nitrogen Fixation Part 1 Ammonification Denitrification Denitrifying Bacteria Ecological Importance of Denitrification Nitrogen Assimilation Transamination Glutamate Dehydrogenase (GDH) Glutamate Synthase Pathway Glutamine Synthetase (GS) Reaction Glutamate Synthase (GOGAT) Reaction Transaminase Reactions Glutamine Synthtase Adenylylation and Deadenylylation

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