Question

Aldolate shows no activity if it is incubated with iodoacetic acid before fructose-1,6-bisphosphate is added to the reaction mixture. What causes this loss of activity?

Short answer

The answer is,

Conformational change due to the addition of a substituent.

Step-by-step solution

Catalysis

The catalysis involves the use of catalyst components to initiate or to increase the rate of a reaction by providing proper orientation to the functional groups present in the compound.

Explanation

The cysteine residues react with iodoacetic acid because a thiol is a good nucleophile and iodine is a good leaving group. If a cysteine residue is at the active site of an enzyme, adding a substituent to the sulfur in this way could interfere with the enzymes being able to bind the substrate or it could interfere with positioning the tyrosine residue that catalyzes the reaction. Adding a substituent to cysteine might also causes a conformational change in the enzyme that could destroy its activity.