Q84
General ScienceBiology
The most abundant enzyme in the living world is _____.
- a.Lipase
- b.DNase
- c.Zymase
- d.Rubisco
Answer: (D) Rubisco
RuBisCO (ribulose-1,5-bisphosphate carboxylase-oxygenase) is the enzyme that fixes atmospheric carbon dioxide in the first step of the Calvin ($C_3$) cycle in the chloroplast stroma. Because it works slowly, green plants and algae make it in huge quantities, and it is regarded as the most abundant enzyme, indeed the most abundant protein, on Earth. It can also bind oxygen, which causes wasteful photorespiration; $C_4$ plants such as maize and sugarcane avoid this by first fixing carbon dioxide with PEP carboxylase. The distractors: lipase digests fats, DNase breaks down DNA, and zymase is the yeast enzyme complex that ferments sugar to alcohol. The most abundant protein in animals is collagen.