A series of enzymes catalyze the reaction X → Y → Z → A. ...

[Hawke]

A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme.

What is substance X?
A) a coenzyme
B) an allosteric inhibitor
C) a substrate
D) an intermediate
E) the product

[Sandstorm]

Try C. I remember this question on my exam.

[Hawke]

Thanks, it was correct.