Question

Physiology and biochemistry of nitrogen fixation biology discussion

Answer 1

biological nitrogen fixation is carried out by some bacte­ria, cyanobacteria and symbiotic bacteria. In symbiotic association, the bacterium provides fixed nitrogen (NH3) to the host and derives carbohydrates and other nutrients from the latter.

Biological nitrogen fixation occurs in the presence of the enzyme nitrogenase which is found inside the nitrogen fixing prokaryote. In addition to this enzyme, a source of reducing equivalents (ferredoxin (Fd) or flavodoxin in vivo), ATP and protons are required.

The overall stoichiometry of biological nitrogen fixation is represented by the following equation:

N2 + 8H+ + 8e– + 16 ATP → 2NH3 + H2 + 16 ADP + 16 Pi

The enzyme nitrogenase is in-fact an enzyme complex which consists of two metallo-proteins.

(i) Fe-protein or iron-protein component (previously called as azo ferredoxin) 

) Fe Mo-protein or iron-molybdenum protein component (previously called as molybdoferredoxin). None of these two components alone can catalyse the reduction of N2 to NH3.

The Fe-protein component of nitrogenase is smaller than its other component and is an Fe-S protein which is extremely sensitive to O2 and is irreversibly inactivated by it. This Fe-S protein is a dimer of two similar peptide chains each with a molecular mass of 30-72 kDa (depending upon the micro-organism). This dimer contains four Fe atoms and four S atoms (which are labile and 12 titrable thiol groups).

The MoFe-protein component of nitrogenase is larger of the two components and consists of two different peptide chains which are associated as a mixed (α2β2 ) tetramer with a total molecular mass of 180 – 235 k Dalton (depending upon the micro-organism). This tetramer contains two Mo atoms, about 24 Fe atoms, about 24 labile S atoms and 30 titrable thiol groups probably in the form of three 24 Fe4 – S4 clusters. This component is also sensitive to O2.

i. Because nitrogenase enzyme complex is sensitive to O2, biological nitrogen fixation requires anaerobic conditions. If the nitrogen fixing organism is anaerobic than there is no such problem. But, even when the organism is aerobic, nitrogen fixation occurs only when conditions are made to maintain very low level of O2 or almost anaerobic conditions prevail inside them around the enzyme nitrogenease.

ii. Apart from N2, the enzyme nitrogenase can reduce a number of other substrates such as N2O (nitrous oxide), N3– (azide), C2H2 (acetylene), protons (2H+) and catalyse hydrolysis of ATP.

iii. Direct measurement of nitrogen fixation is done by mass spectroscopy. However, for comparative studies reduction of acetylene can be measured rather easily by gas chromatography method.

The electrons are transferred from reduced ferredoxin or flavodoxin or other effective reducing agents to Fe-protein component which gets reduced. From reduced Fe-protein, the elec­trons are given to MoFe-protein component which in turn gets reduced and is accompanied by hydrolysis of ATP into ADP and inorganic phosphate (Pi). Two Mg++ and 2 ATP molecules are required per electron transferred during this process.

Binding of 2 ATPs to reduced Fe-protein and subsequent hydrolysis of 2 ATPs to 2 ADP + 2 Pi is believed to cause a conformatorial change of Fe-protein which facilitates redox (reduction-oxidation) reactions. From reduced MoFe-protein, the electrons are finally transferred to molecular nitrogen (N2) and 8 protons, so that two ammonia and one hydrogen molecule are produced

iv. At first glance, it might be expected that six electrons and six protons would be required for reduc­tion of one N2 molecule to two molecules of ammonia. But, the reduction of N2 is obligatorily linked to the reduction of two protons to form one H2molecule also. It is believed that this is necessary for the binding of nitrogen at the active site.

v. The electrons for regeneration of reduced electron donors (ferredoxin, flavodoxin etc.) are provided by the cell metabolism e.g., pyruvate oxidation.

Substantial amount of energy is lost by the micro-organisms in the formation of H2mol­ecule during nitrogen fixation. However, in some rhizobia, hydrogenase enzyme is found which splits H2 to electrons and protons (H2 → 2H+ + 2e–). These electrons may then be used again in reduction of nitrogen, thereby increasing the efficiency of nitrogen fixation.

Although scientists have tried to explain the mechanism of biological nitrogen fixation, but the precise pathway of electron transfer, substrate entry and product release and source of protons during biological nitrogen

it is from net I hope it will be use ful to you pls mark as brainly answer if it is correct

Answer 2

Physiology and biochemistry of nitrogen fixation biology is also known as Biological Nitrogen Fixation.

Explanation:

• This process  Nitrogen Fixation is carried out  in the presence of the enzyme nitrogenase by specific prokaryotes.
• The process uses the nitrogenase enzymes which helps in catalyzing the conversion of nitrogen in the air to ammonia.
• The atmospheric nitrogen is included into the tissues of some plants for the conversion into ammonia.
• They have the capability to gain nitrogen, from the microbes present in the soil.
• legumes available as foliage plants can get nitrogen from the atmosphere.
• Biological nitrogen fixation is carried out by cyanobacteria and symbiotic bacteria.
• In symbiotic association, the bacterium will give fixed nitrogen (NH3) to the host cells.
• They derives carbohydrates and nutrients from the host cells.
• Biological nitrogen fixation is represented by the following equation:
• $N2 + 8H+ + 8e^{-} + 16 ATP ----- 2NH3 + H2 + 16 ADP + 16 Pi$

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