Q.25 The most abundant enzyme on Earth is
l. Carbonic anhydrase
2. Ribulose l, 5-bisphosphate carboxylase/oxygenase.
3. Acetylcholine esterase
4. Urease
Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is the most abundant enzyme on Earth, making option 2 correct.
Option Analysis
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Option 1: Carbonic anhydrase. Incorrect. This zinc metalloenzyme catalyzes CO₂ hydration to bicarbonate, abundant in red blood cells and kidneys for pH/respiratory balance, but far less prevalent globally than photosynthetic enzymes.
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Option 2: Ribulose 1,5-bisphosphate carboxylase/oxygenase. Correct. RuBisCO fixes CO₂ in the Calvin cycle of photosynthesis, comprising 20-50% of leaf soluble protein across all photosynthetic organisms; ~0.7 billion tonnes exist planet-wide, produced at ~1000 kg/second.
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Option 3: Acetylcholine esterase. Incorrect. This hydrolyzes ACh at synapses, essential for nerve transmission but limited to neural tissues, not widespread like plant enzymes.
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Option 4: Urease. Incorrect. Nickel-dependent urease hydrolyzes urea (first crystallized enzyme by Sumner), abundant in microbes/plants but negligible compared to RuBisCO’s photosynthetic role.
Introduction to Most Abundant Enzyme
The most abundant enzyme on Earth is Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO), vital for CO₂ fixation in photosynthesis across plants, algae, and bacteria. Comprising ~44 kg per human via food chains, its ubiquity stems from powering the Calvin cycle, key for GATE Life Sciences plant physiology.
Why RuBisCO Dominates
RuBisCO catalyzes RuBP + CO₂ → 3-PGA, enabling ~90% of Earth’s biomass carbon fixation despite low efficiency (also oxygenase causing photorespiration). Present in chloroplasts (15-30% soluble protein), global synthesis supports planetary productivity.
| Enzyme | Abundance Context | Primary Role |
|---|---|---|
| RuBisCO | 0.7 billion tonnes globally | Photosynthesis CO₂ fixation |
| Carbonic anhydrase | High in blood/kidneys | CO₂ transport |
| Acetylcholine esterase | Neural synapses | Neurotransmission |
| Urease | Microbes/plants | Urea hydrolysis |
Biological and Exam Importance
RuBisCO’s abundance reflects photosynthesis’s scale; engineering better variants boosts crop yields. Exams test vs. others like carbonic anhydrase (animal-focused).
