Question

With regard to the biological nitrogen fixation by Rhizobium in association with soybean, which one of the following statement/statements does not hold true?
A. Nitrogenase may require oxygen for its functioning
B. Nitrogenase is a Mo-Fe protein
C. Leghemoglobin is a pink coloured pigment
D. Nitrogenase helps to convert $N_2$ gas into two molecules of ammonia.

Answer 1

The most important enzyme of nitrogen fixation is the enzyme nitrogenase and it is sensitive to a particular gas present in the atmosphere which is harmless to humans.

Complete answer:
In order to arrive at the correct answer, we must first know the basic definition of some words.
1. Nitrogen fixation-Nitrogen fixation is the process by which nitrogen present in the atmosphere which is primarily molecular nitrogen is converted into ammonia or other nitrogenous compounds in the soil. The fixation helps plants to take up nitrogen for their growth and development.
2.Leghaemoglobin -It is a specific type of compound mainly an oxygen carrier and hemoprotein that is found in the root nodules of leguminous plants that carry out nitrogen fixation. The main function of leghemoglobin is the protection of the enzyme nitrogenase from atmospheric oxygen.
3. Mo-Fe protein-It is a tetrameric protein that consists of two alpha and two beta subunits respectively. It also contains two sulphur clusters respectively.
4. Nitrogenase-The enzyme nitrogenase is an important enzyme found in certain bacteria. It is an important enzyme that reduces nitrogen to ammonia that is a very important step in the biological nitrogen fixation process .It is the only enzyme that catalyzes this type of reaction and functions without the presence of oxygen.

Hence, the correct answer is option (A).

Note: Nitrogen fixation is a very important process in biological systems. It helps in the biosynthesis of all nitrogen containing compounds in the body for example amino acids, proteins and nucleic acids. The enzyme nitrogenase is a very important enzyme that plays a very important part in nitrogen fixation. Leghaemoglobin is present to protect it from the atmospheric oxygen that might lead to its disruption of function.