Answer: Enzyme-substrate complex is formed a substrate binds to the active site in a free enzyme.
Step-by-step explanation:
Enzyme-substrate complex is a transient intermediate in any enzyme catalyzed reaction. The substrate (S) binds to the catalytic or active site of a free enzyme (E) to form enzyme-substrate complex (ES) which breaks down to yield the free enzyme and the reaction product (P). The enzyme is then free to catalyze reaction of another molecule of the substrate. The equation: E + S <--> ES. The formation of the enzyme-substrate complex is a reversible reaction.