What role does magnesium play in the reaction catalyzed by phosphoglucoisomerase?

• A. It acts as a competitive inhibitor, slowing down the reaction.
• B. It is a substrate for the enzyme, necessary for the reaction to occur.
• C. It is not involved in the reaction.
• D. It stabilizes the transition state, facilitating the isomerization of glucose 6-phosphate.

Answer: (D)