Step 1: Understanding the Question:
The question asks to identify the enzyme that is missing or non-functional in individuals suffering from the genetic disorder Phenylketonuria (PKU).
Step 2: Key Formula or Approach:
PKU is an inborn error of metabolism involving the amino acid phenylalanine.
Step 3: Detailed Explanation:
In a healthy individual, the amino acid phenylalanine is converted into the amino acid tyrosine by the enzyme phenylalanine hydroxylase (PAH).
In PKU patients, a mutation in the PAH gene leads to a deficiency of this enzyme. This causes:
1. Accumulation of phenylalanine in the blood.
2. Conversion of phenylalanine into phenylpyruvic acid (a ketone) and other derivatives.
3. These substances accumulate in the brain, leading to intellectual disabilities if not managed with a strict diet.
Step 4: Final Answer:
The deficient enzyme is Phenylalanine hydroxylase.