How does the inhibition constant for the free enzyme (KI) differ from the inhibition constant for the enzyme-substrate complex (K'I)?

• A. KI measures the binding affinity of the enzyme-substrate complex for the inhibitor, while K'I measures the binding affinity of the free enzyme for the inhibitor.
• B. KI and K'I both measure the binding affinity of the enzyme-substrate complex for the inhibitor.
• C. KI and K'I both measure the binding affinity of the free enzyme for the inhibitor.
• D. KI measures the binding affinity of the free enzyme for the inhibitor, while K'I measures the binding affinity of the enzyme-substrate complex for the inhibitor.

Answer: (D)