If a Drug Is Designed to Denature Enzymes Involved in Digesting

If a drug is designed to denature enzymes involved in digesting phenylalanine,why would patients treated with this drug develop phenylketonuria?

A) They lack an enzyme to break down phenylalanine.
B) They lack an enzyme to produce phenylalanine.
C) They produce too much phenylalanine.
D) They lack an inhibitor of an enzyme to break down phenylalanine.
E) They eat more phenylalanine than most people.