Q. Which of the following best describes a zymogen?
Answer: An inactive enzyme precursor activated by limited proteolysis
Notes: Zymogens are inactive enzyme precursors activated by specific peptide cleavage, such as trypsin from trypsinogen and pepsin from pepsinogen. This activation mechanism prevents damage from premature enzyme action. Option 1 refers to irreversible inhibition, 3 to metalloenzymes, and 4 to ribozymes like the ribosomal peptidyl transferase, not zymogens.