Step 1: Understanding the Question:
We need to identify the enzyme whose defect leads to albinism, a condition where the skin, hair, and eyes lack normal pigment.
Step 2: Key Concept:
Melanin, the pigment responsible for skin and hair color, is made inside melanocytes through a chain of reactions starting from the amino acid tyrosine. Whichever enzyme drives the first step of that chain is the one to look for.
Step 3: Detailed Explanation:
The pathway begins when tyrosine is converted to DOPA, and then DOPA is converted to dopaquinone, both steps driven by the same copper dependent enzyme, tyrosinase. Dopaquinone then goes on to form the pigment melanin. If the gene for tyrosinase carries a mutation, this enzyme either does not work or works poorly, so the pathway stops near its very first step and little or no melanin is produced, giving the pale skin, light hair, and light eyes seen in albinism.
Beta-hydroxylase acts in a completely different pathway, turning dopamine into norepinephrine for the nervous system, and plays no part in skin pigmentation.
Pyruvate dehydrogenase belongs to carbohydrate metabolism, feeding pyruvate into the citric acid cycle for energy production, again unrelated to melanin.
Hydroxylase by itself is too generic a term, since many different hydroxylase enzymes exist across the body for many different reactions, and it does not specifically identify the melanin pathway enzyme.
Step 4: Final Answer:
Tyrosinase is the enzyme responsible for albinism when it is defective.