How does the rate-limiting step of an enzyme-catalyzed reaction affect kcat and the overall reaction rate?

• A. The rate-limiting step increases the overall reaction rate by increasing kcat.
• B. The rate-limiting step only affects the binding affinity of the enzyme.
• C. The rate-limiting step has no effect on kcat or the overall reaction rate.
• D. The rate-limiting step determines kcat, which in turn dictates the maximum possible reaction rate.

Answer: (D)