Question

Rubisco activase is a (an)

(A). Catalytic chaperone
(B). ATP-dependant enzyme
(C). Enzyme that activates Rubisco by promoting the entry of sugar phosphates to its active site
(D). Enzyme that activates Rubisco by increasing its carbamylation

Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A), (B) and (C) only.
• C. (B) and (C) only.
• D. (A) and (D) only.

Hint:

Remember that Rubisco activase acts to clear the active site of Rubisco, allowing the essential activating carbamylation to occur.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Rubisco (Ribulose-1,5-bisphosphate carboxylase-oxygenase) is the primary enzyme responsible for carbon dioxide fixation in photosynthesis, but its active site can easily become blocked by inhibitory sugar phosphates.

Step 2: Detailed Explanation:
- (A) is correct because Rubisco activase (RCA) is a specialized AAA+ protein that acts as a catalytic chaperone, physically remodeling Rubisco to restore its activity.
- (B) is correct because RCA utilizes the energy of ATP hydrolysis to induce structural changes in Rubisco.
- (C) is incorrect because RCA activates Rubisco by promoting the *release* (removal) of tightly bound inhibitory sugar phosphates (like RuBP or carboxyarabinitol 1-phosphate) from the inactive active site, not their entry.
- (D) is correct because removing these inhibitory sugar phosphates exposes the active-site lysine residue (Lys-201). This allows the lysine to react with \( \text{CO}_2 \) and bind \( \text{Mg}^{2+} \) (carbamylation), which is required to form the active enzyme complex.
Thus, statements (A), (B), and (D) are correct.

Step 3: Final Answer:
Hence, the correct option is (A).