Which type of enzyme inhibition occurs when an inhibitor binds only to the enzyme-substrate complex?

Which type of enzyme inhibition occurs when an inhibitor binds only to the enzyme-substrate complex?

• A. Uncompetitive inhibition
• B. Competitive inhibition
• C. Noncompetitive inhibition
• D. Irreversible inhibition

Answer: (A)

Uncompetitive inhibition occurs when the inhibitor binds only to the enzyme-substrate complex, not to the free enzyme. This binding forms an ESI complex that cannot proceed to product, effectively locking the substrate in place and stopping turnover. Because the inhibitor requires the substrate to be bound first, increasing substrate concentration creates more ES complexes for the inhibitor to bind, so the inhibition becomes stronger at higher substrate levels. Kinetically, both Vmax and Km appear reduced. Vmax drops because fewer enzyme–substrate complexes are able to proceed to product, while Km appears reduced because the inhibitor binding to ES shifts the apparent equilibrium toward ES, making the enzyme seem to have higher affinity for the substrate. On a plot of 1/v versus 1/[S], this results in parallel lines for different inhibitor concentrations, reflecting proportionate decreases in both parameters.

Uncompetitive inhibition occurs when the inhibitor binds only to the enzyme-substrate complex, not to the free enzyme. This binding forms an ESI complex that cannot proceed to product, effectively locking the substrate in place and stopping turnover. Because the inhibitor requires the substrate to be bound first, increasing substrate concentration creates more ES complexes for the inhibitor to bind, so the inhibition becomes stronger at higher substrate levels.

Kinetically, both Vmax and Km appear reduced. Vmax drops because fewer enzyme–substrate complexes are able to proceed to product, while Km appears reduced because the inhibitor binding to ES shifts the apparent equilibrium toward ES, making the enzyme seem to have higher affinity for the substrate. On a plot of 1/v versus 1/[S], this results in parallel lines for different inhibitor concentrations, reflecting proportionate decreases in both parameters.