Which of the following statements is incorrect about allosteric enzymes?

A. The activity of an allosteric enzyme can be controlled by a regulatory molecule. This is true. Remember, the regulatory molecule or effector molecule can either help to increase or decrease the rate of the reaction by affecting the active site of the enzyme. So this is true.

Allosteric enzymes have 2 types of binding sites. So this is also true. Remember, there are 2 ways in which we can affect the overall binding sites. We can have positive or negative.

The binding of an allosteric regulator to an enzyme can change the availability of an active site. Yes. A positive regulator can increase the rate of reaction by opening up an active site, whereas a negative one can close up an already present active site as soon as it binds to the allosteric site.

The overall shape of an allosteric enzyme always remains the same. No. Once a regulatory molecule or effector molecule attaches to the allosteric site, this can open up or close an active site. This would cause a change in the overall shape of the enzyme. So here, option d is a statement that's incorrect about allosteric enzymes.