RuBisCO enzyme catalyzes carboxylation or oxygenation of RuBP in five steps. Following are certain statements regarding the catalysis carried out by RuBisCO:

A. The first step of catalysis is enolization of RuBP.
B. The carbon-carbon bond between C3 and C4 of RuBP is cleaved.
C. Carboxylase activity produces only one molecule of 3-phosphoglycerate.
D. Oxygenase activity produces one molecule of 3-phosphoglycerate and one molecule of 2-phosphoglycolate.

Which one of the following options represents the combination of all correct statements?

Correct option is D

Sol.

• A is correct: The first step in RuBisCO catalysis is the enolization of RuBP, forming an enediol intermediate necessary for subsequent reactions.

• D is correct: The oxygenase activity of RuBisCO produces one molecule of 3-phosphoglycerate and one molecule of 2-phosphoglycolate, leading to photorespiration.

• B is incorrect: The carbon-carbon bond cleavage between C3 and C4 occurs later in the mechanism, not as an initial event, and this statement is less emphasized as “first step.”

• C is incorrect: The carboxylase activity produces two molecules of 3-phosphoglycerate, not just one.

Information Booster:

• RuBisCO’s dual role in carbon fixation and photorespiration is critical for plant metabolism.

• Enolization is a key initial step facilitating the attack on CO₂ or O₂.

• Photorespiration via oxygenase activity reduces photosynthetic efficiency due to production of 2-phosphoglycolate.