In general, how many times can a single enzyme molecule be used to catalyze a reaction before it is consumed?

• A. It can be used repeatedly for many catalytic cycles because it is not consumed by the reaction (until it is denatured or inhibited).
• B. It can be used exactly twice because enzymes have two active sites that are used once each.
• C. It can be used only once because it is converted into product during catalysis.
• D. It can be used a fixed number of times equal to the reaction stoichiometric coefficient for the enzyme.

Answer: (A)