Aminolevulinate dehydratase (ALAD ) is an enzyme that relies on zinc as a coenzyme. A zinc ion binds to the ALAD active site, where it forms favorable interactions with the side chains of three amino acids. Researchers have found that substituting a lead ion for a zinc ion in the ALAD active site causes inhibition of ALAD . Which of the following statements best helps explain how the lead ion causes inhibition of ALAD ?

a. It changes the shape and charge of the substrate so that it becomes more compatible with ALAD’s active site.
b. It changes the amino acid sequence of the ALAD protein so that the enzyme catalyzes a different reaction.
c.It changes the three-dimensional structure of the active site so that ALAD is no longer compatible with its substrate.
d. It changes the enzyme-substrate complex so that the transition state is more stable and the reaction proceeds at a faster rate.

Co-factors are molecules that are required by an enzyme to perform its function of catalysis. If a wrong co-factor binds to the enzyme then it will change the three-dimensional structure of the enzyme and the substrate will no longer fit into the enzyme. Hence, Option C is the best choice that explains the inhibition of ALAD.

Other options are false because :

Option A: The wrong co factor will not affect the substrate nor will it make it compatible for ALAD's active site.

Option B: The wrong factor doesn't change the amino acid sequence of the protein or enzyme, rather it changes the three dimensional structure of the enzyme.

Option D : The wrong co factor won't allow the reaction to proceed at a faster rate, rather it will inhibit the reaction.