Question

During glycolysis, the enzyme phosphoglycerate mutase catalyses the conversion of 3-phosphoglycerate (3PG) to 2-phosphoglycerate (2PG) through formation of 2,3-bisphosphoglycerate (2,3-BPG) intermediate. The phosphoryl group to 3PG for the formation of 2,3-BPG is transferred from which of the followings:

• A. Adenosine triphosphate
• B. Acetyl phosphate
• C. Pyrophosphate
• D. Phospho-histidine residue present at the active site of the phosphoglycerate mutase

Hint:

Occasionally, the 2,3-BPG intermediate can dissociate from the enzyme, leaving it in an inactive, unphosphorylated state. Traces of free 2,3-BPG are required in the cell to re-phosphorylate the active-site histidine and keep the enzyme active.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Phosphoglycerate mutase (PGM) catalyzes the reversible isomerization of 3-phosphoglycerate (3-PG) to 2-phosphoglycerate (2-PG) during glycolysis.
This reaction proceeds through a double-displacement mechanism involving a transient, covalently modified enzyme intermediate.

Step 2: Detailed Explanation:
The active form of phosphoglycerate mutase contains a highly reactive phospho-histidine residue at its catalytic center.
The enzyme operates through a two-step mechanism:
1. First Step: The phosphoryl group attached to the active-site histidine residue is transferred directly to the hydroxyl group at carbon-2 of the incoming 3-phosphoglycerate (3-PG).
This transiently converts the substrate into 2,3-bisphosphoglycerate (2,3-BPG) within the active site.
2. Second Step: The same active-site histidine residue then acts as an acceptor, removing the original phosphoryl group from carbon-3 of the 2,3-BPG intermediate.
This step regenerates the active phospho-histidine residue on the enzyme and releases 2-phosphoglycerate (2-PG) as the final product.
This entire reaction cycle does not require free ATP, acetyl phosphate, or pyrophosphate as a direct donor, as the phosphoryl group is transferred directly from the enzyme's catalytic histidine residue.

Step 3: Final Answer:
The phosphoryl group is transferred from the phospho-histidine residue present at the active site of the phosphoglycerate mutase, which corresponds to option (D).