To protect the oxygen-sensitive nitrogenase, symbiotic nodules contain leghemoglobin, which binds oxygen with high affinity, maintaining an anaerobic state while delivering sufficient oxygen for bacterial respiration.
Step 1: Understanding the Concept:
Nitrogenase is the multi-subunit enzyme complex responsible for catalyzing biological nitrogen fixation, converting atmospheric dinitrogen (\(N_2\)) into ammonia (\(NH_3\)). Key Formula or Approach:
The balanced chemical equation for the reduction of dinitrogen catalyzed by nitrogenase is:
\[ N_2 + 8H^+ + 8e^- + 16\text{ATP} \rightarrow 2NH_3 + H_2 + 16\text{ADP} + 16P_i \] Step 2: Detailed Explanation:
Let us analyze each of the stated options based on the biochemistry of the nitrogenase enzyme complex:
Sensitivity to Oxygen Environment: The nitrogenase enzyme complex consists of two main proteins: the Fe-protein (dinitrogenase reductase) and the MoFe-protein (dinitrogenase). Both components are extremely sensitive to molecular oxygen (\(O_2\)) and are rapidly and irreversibly denatured upon exposure to it. Therefore, nitrogenase requires a strictly anaerobic microenvironment to function, making options (A) and (D) incorrect.
Cofactor Composition: The core active site of the MoFe-protein contains a specialized metal cluster called the iron-molybdenum cofactor (FeMo-co). It does not contain magnesium as a built-in inorganic activator in its active site structure, although magnesium ions (\(Mg^{2+}\)) are required in the cytosol to bind ATP (\(Mg\text{-ATP}\)) before it can interact with the Fe-protein. Thus, option (B) is incorrect.
Reaction Products: As shown in the balanced biochemical equation, for every molecule of dinitrogen (\(N_2\)) reduced, the enzyme complex utilizes 8 protons and 8 electrons, releasing exactly two molecules of ammonia (\(NH_3\)) and one molecule of hydrogen gas (\(H_2\)) as products. Thus, option (C) is correct. Step 2: Final Answer:
The correct option is (C), which states that nitrogenase releases two \(NH_3\) molecules as products.
