Final answer:
A Schiff base is formed between the ketone of acetoacetate and a lysine residue in the active site of the enzyme during its catalyzed decarboxylation.
Step-by-step explanation:
In the enzyme-catalyzed decarboxylation of acetoacetate, a Schiff base is formed between the ketone of acetoacetate and a lysine residue in the active site of the enzyme. This type of reaction involves the condensation of lysine with the substrate, where the enzyme active site provides a conducive environment for the reaction to occur more efficiently. The Schiff base formation typically involves the free amino group of lysine reacting with the carbonyl group of acetoacetate to facilitate the decarboxylation process.