Nitrogenous enzyme first isolated from

✅Explanation:
-The nitrogenous enzyme referred to in the question is nitrogenase.
-Nitrogenase is responsible for the crucial process of biological nitrogen fixation, converting atmospheric nitrogen (N2) into ammonia (NH3), a form usable by plants.
-Clostridium pasteurianum, an anaerobic bacterium, was the first organism from which the nitrogenase enzyme complex was successfully isolated and characterized. This groundbreaking discovery significantly advanced our understanding of nitrogen fixation.

🔑Key Points:
Biological Nitrogen Fixation (BNF) – 
-Atmospheric nitrogen cannot be absorbed directly by the plants so it is first converted into stable compound ammonia (NH3) in the roots, with the help of symbiotic bacteria this is called biological nitrogen fixation
-N2 → N2H2 → N2H4 → 2NH3
-The enzyme nitrogenase is responsible for the biological nitrogen fixation.
-It is a Mo-Fe protein that catalyses the reduction of atmospheric nitrogen (molecular nitrogen) to ammonia, the first stable product of nitrogen fixation.
-Molybdenum acts as an activator for nitrogenase during nitrogen fixation.
-The enzyme, nitrogenase which is capable of nitrogen reduction is present exclusively in prokaryotes. Such microbes are called N2- fixers. 
-The nitrogen-fixing microbes could be free-living or symbiotic.
-Examples of free-living nitrogen-fixing aerobic microbes are Azotobacter and Beijerinckia while Rhodospirillum is anaerobic and free-living.
🛑Additional Information  
-The enzyme nitrogenase is highly sensitive to molecular oxygen; it requires anaerobic conditions.
-The nodules have adaptations that ensure that the enzyme is protected from oxygen.
-To protect these enzymes, the nodule contains an oxygen scavenger called leg-haemoglobin