Allosteric enzymes can control their output of product by

Conformational change

Explanation:

To understand how allosteroic enzymes work, one has to know how enzymatic reactions are executed. See below:

A ⇒ B

A: Represents the substrate of the reaction

B: Represents the product of the reaction

E: Represents the enzyme that catalyzes this reaction

Enzymatic reactions normally are controlled by the amount of substrate (A) or product (B) present in the environment. One way enzymes can control the reaction rate is through the presence of allosteric sites. These are specialized regions capable of binding molecules called effectors, causing a conformational change in the enzyme which leads to either acceleration or stalling of the reaction (depending on the specific enzyme and/or effector under study). Both substrates (A) and products (B) may act as effectors, resulting in, respectively, acceleration and slowing of the reaction.