29-06-2013, 12:04 PM
NITROGEN FIXATION
[attachment=56212]
Introduction
Important step in nitrogen cycle
Provides Nitrogen for plants in the form of soluble nitrates.
Nitrogen can also be fixed industrially by Haber process.
Biological nitrogen fixation requires nitrogenase enzyme.
Transition elements require Mo and Fe
Nitrogen fixing Microorganisms
Called as vivo nitrogen fixation.
There are two groups of microorganisms.
1 Free bacteria (asymbiotic)
eg. Azatobactor (areobic)
Clostridium pasterianum (anaerobic)
2 Symbiotic microorganisms
eg. Rizobium in root nodules of leguminous plants
Nitrogenase
Enzyme responsible for nitrogen fixation.
Made up of two proteins
1) iron protein (homodimeric)
2)molybdenum iron protein (heterotetrameric)
Activity is due to combined effect of both
Both contains sulphide ions equal to no. of Fe atoms
Present as Fe4S4 clusters which is system for electron storage.
It is anaerobic complex.
Rubredoxin Protein
Originally isolated from Clostridium pasteurianum
One iron atom and four cysteine residue per molecule of protein
Mol. Wt=6000 and 54 amino acid residues.
Oxidized is red and reduced is colourless.
Hydrogenase
Hydrogenases were first discovered in the 1930s.
A hydrogenase is an enzyme that catalyses the reversible oxidation of molecular hydrogen (H2).
Hydrogenases play a vital role in anaerobic metabolism.
Hydrogenases were classified according to the metals thought to be at their active sites.
Iron-only ([FeFe]), nickel-iron ([NiFe]), and "metal-free".
[attachment=56212]
Introduction
Important step in nitrogen cycle
Provides Nitrogen for plants in the form of soluble nitrates.
Nitrogen can also be fixed industrially by Haber process.
Biological nitrogen fixation requires nitrogenase enzyme.
Transition elements require Mo and Fe
Nitrogen fixing Microorganisms
Called as vivo nitrogen fixation.
There are two groups of microorganisms.
1 Free bacteria (asymbiotic)
eg. Azatobactor (areobic)
Clostridium pasterianum (anaerobic)
2 Symbiotic microorganisms
eg. Rizobium in root nodules of leguminous plants
Nitrogenase
Enzyme responsible for nitrogen fixation.
Made up of two proteins
1) iron protein (homodimeric)
2)molybdenum iron protein (heterotetrameric)
Activity is due to combined effect of both
Both contains sulphide ions equal to no. of Fe atoms
Present as Fe4S4 clusters which is system for electron storage.
It is anaerobic complex.
Rubredoxin Protein
Originally isolated from Clostridium pasteurianum
One iron atom and four cysteine residue per molecule of protein
Mol. Wt=6000 and 54 amino acid residues.
Oxidized is red and reduced is colourless.
Hydrogenase
Hydrogenases were first discovered in the 1930s.
A hydrogenase is an enzyme that catalyses the reversible oxidation of molecular hydrogen (H2).
Hydrogenases play a vital role in anaerobic metabolism.
Hydrogenases were classified according to the metals thought to be at their active sites.
Iron-only ([FeFe]), nickel-iron ([NiFe]), and "metal-free".