Question

If the phosphorus atom in 3-phosphoglycerate is radioactively labeled, where will the label be when the reaction that forms 2-phosphoglycerate is over?

Short answer

Isotope labeling of 3-phosphoglycerate will be in the phosphate group attached to the enzyme phosphoglycerate mutase.

Step-by-step solution

Radioactive labeling

Radioactive labeling is a method that is used to determine the reaction mechanism.

In this method, the reactant is labeled by replacing a specific atom with its radioactive isotope; when the reaction has completed, the position of the labeled radioactive isotope is measured.

Step 2: Radioactively labeling of 3-phosphoglycerate 

Phosphoglycerate mutase (PGM) is an enzyme that catalyzes step 8 of glycolysis - the internal transfer of a phosphate group from C-3 to C-2, which results in the conversion of 3-phosphoglycerate to 2-phosphoglycerate through a 2,3-bisphosphoglycerate intermediate.

Thus the phosphorus atom in 3-phosphoglycerate, which is radioactively labeled, the labeled phosphorous will be on the “phosphate group” that is attached to the enzyme phosphoglycerate mutase when the reaction forms 2-phosphoglycerate.