Question

The mechanism involved in the reaction catalyzed by phosphoglyceromutase is known to involve a phosphorylated enzyme intermediate. If 3 -phosphoglycerate is radioactively labeled with "P, the product of the reaction, 2-phosphoglycerate, does not have any radioactive label. Design a mechanism to explain these facts.

Short answer

The phosphate group from 3-phosphoglycerate is transferred to the enzyme, which then provides a non-radioactive phosphate to form 2-phosphoglycerate.

Step-by-step solution

- Identify the Substrate

The initial substrate in the reaction catalyzed by phosphoglyceromutase is 3-phosphoglycerate, which is radioactively labeled with phosphorus-32 (P-32).

- Enzyme Phosphorylation

Phosphoglyceromutase has a phosphorylated enzyme intermediate, meaning the enzyme itself temporarily acquires a phosphate group during the reaction process.

- Transfer of Phosphate Group to the Enzyme

3-phosphoglycerate transfers its radioactive phosphate group to the enzyme. This results in the enzyme being phosphorylated and the formation of glycerate-3 without any radioactive label.

- Formation of the Intermediate

A non-radioactive phosphate from the enzyme is then transferred to the previously formed glycerate-3, creating the intermediate 2,3-bisphosphoglycerate.

- Removal of Phosphate from the Intermediate

2,3-bisphosphoglycerate then donates one of its phosphate groups back to the enzyme, leaving behind 2-phosphoglycerate, which is not radioactively labeled because it received a non-radioactive phosphate.

- Product Formation

The final product of the reaction is 2-phosphoglycerate, which does not contain any radioactive label as all the radiolabeled phosphate groups were returned to the enzyme during the process.

Key concepts

phosphorylated enzyme intermediate

Phosphoglyceromutase catalyzes the conversion of 3-phosphoglycerate to 2-phosphoglycerate. A key aspect of this process is the formation of a phosphorylated enzyme intermediate.
This occurs when the enzyme temporarily holds onto a phosphate group. In our reaction, the enzyme initially gains the radioactive phosphate from 3-phosphoglycerate. This step is crucial as it activates the enzyme for the next stages of the conversion process.
It is this ability of the enzyme to be phosphorylated that enables it to facilitate the transfer of phosphate groups efficiently, without the radioactive label being part of the final product.

• Important for the enzyme’s function.
• It helps in the transfer of phosphate groups.
• This intermediate stage is temporary yet essential.

radioactive labeling

In the given mechanism, radioactive labeling helps to track the phosphate group within the reaction. Here, 3-phosphoglycerate is labeled with a radioactive isotope of phosphorus, phosphorus-32 (P-32).
This label allows us to trace the movement of the phosphate group as the reaction proceeds. Although the substrate starts radioactive, the final product, 2-phosphoglycerate, does not have any radioactive label.

• Radioactive labeling is a tracking method.
• Helps in studying the phosphate group transfer.

phosphate group transfer

Phosphate group transfer is a fundamental event in the reaction catalyzed by phosphoglyceromutase. During this process:

• The radioactive phosphate group from 3-phosphoglycerate is first transferred to the enzyme.
• The enzyme then provides a non-radioactive phosphate group to form 2,3-bisphosphoglycerate.
• This intermediate then loses one of its phosphate groups, which is returned to the enzyme, leaving behind non-radioactive 2-phosphoglycerate.

These steps ensure the correct rearrangement of phosphate groups without retaining the radioactive label. It highlights the enzyme’s role in shifting phosphates without directly transferring the radioactive tag to the final product.

2-phosphoglycerate

2-phosphoglycerate is the end product of the reaction catalyzed by phosphoglyceromutase. It is formed after the intermediate 2,3-bisphosphoglycerate donates one of its phosphate groups back to the enzyme.
This final phosphate transfer leaves behind a molecule of 2-phosphoglycerate, which lacks the radioactive label because the phosphate it receives from the enzyme is non-radioactive.

2,3-bisphosphoglycerate

2,3-bisphosphoglycerate is a crucial intermediate in the reaction catalyzed by phosphoglyceromutase. After the enzyme receives the radioactive phosphate from 3-phosphoglycerate, the enzyme donates a non-radioactive phosphate group to form 2,3-bisphosphoglycerate.
This intermediate holds two phosphate groups until one is returned to the enzyme, leaving a single phosphate group on the resulting 2-phosphoglycerate molecule.
Understanding this intermediate step is key to grasping how the enzyme manages phosphate groups without transferring the radioactive label to the final product.