RuBisCO is the most abundant enzyme in the world because:

📌Concept:
-RuBisCO stands for Ribulose-1,5-biphosphate carboxylase-oxygenase.
-It is a chief enzyme of the Calvin cycle in photosynthesis. It is present in the stroma.
✅Explanation: 

✏️RuBisCO is called the most abundant enzyme in the world because:
-Its active site can bind with both CO2 and O2 i.e. RuBisCO can act as both carboxylase as well as oxygenase.
-It acts as carboxylase at a lower concentration of oxygen and a higher concentration of carbon dioxide. It catalyzes the process of carboxylation of 5C compound Ribulose-1,5-bisphosphate into a 6C compound 3-phosphoglycerate in the Calvin cycle
-It acts as an oxygenase at a higher concentration of oxygen and a low concentration of carbon dioxide. This causes photorespiration in C3 plants which is a wasteful process.
      2. RuBisCO comprises about 15-50% of total chloroplast proteins.
Thus it can be said that RuBisCO is the most abundant enzyme in the world.