Which of the following is NOT a characteristic of enzymes?
A. They change shape when they bind their substrates.
B. They can catalyze reactions in both forward and reverse directions.
C. Their activity is sensitive to changes in temperature.
D. They are always active on more than one kind of substrate.
Enzymes are substrate-specific. Most enzymes catalyze only one biochemical reaction. Their active sites are specific for a certain type of substrate and do not bind to other substrates and catalyze other reactions.
Therefore, the Correct Answer is D.