Question

Which enzyme is responsible for albinism?

• A. Beta-hydroxylase
• B. Pyruvate dehydrogenase
• C. Hydroxylase
• D. Tyrosinase

Hint:

Remember: Albinism is due to a tyrosinase deficiency — an enzyme vital for melanin biosynthesis. It’s a classic GPAT question from the Biochemistry section.

Answer 1

The Correct Option is D

• Albinism is a congenital disorder characterized by the partial or complete absence of melanin pigment in the skin, hair, and eyes.
• The biosynthesis of melanin occurs via the tyrosine metabolic pathway, in which the enzyme tyrosinase plays a central role. 
• Tyrosinase catalyzes the conversion of tyrosine to DOPA (dihydroxyphenylalanine) and then to dopaquinone, which are key steps in melanin production.
• Mutations in the tyrosinase gene (TYR) result in defective or absent enzyme activity, leading to oculocutaneous albinism type 1 (OCA1).
• This enzyme is copper-dependent and is found in melanocytes. 

Other options:

(a) Beta-hydroxylase — Involved in catecholamine biosynthesis (e.g., norepinephrine production).

(b) Pyruvate dehydrogenase — Part of carbohydrate metabolism; links glycolysis to the Krebs cycle. 

(c) Hydroxylase — General term for enzymes adding hydroxyl groups, but not specific to melanin synthesis.
 

Answer 2

The question asks which enzyme, when defective, causes albinism, a condition marked by little or no pigment in the skin, hair, and eyes. Let's look at each option:

1. Beta-hydroxylase: This enzyme, more precisely dopamine beta-hydroxylase, converts dopamine into norepinephrine as part of catecholamine synthesis. It has no role in making the pigment melanin.
2. Pyruvate dehydrogenase: This enzyme converts pyruvate into acetyl CoA, linking glycolysis to the citric acid cycle. It is central to energy metabolism, not pigment production.
3. Hydroxylase: This is only a general name for a broad class of enzymes that add a hydroxyl group to a substrate. On its own it does not point to any specific enzyme tied to melanin synthesis or albinism.
4. Tyrosinase: This copper containing enzyme, found in melanocytes, catalyzes the first and rate limiting steps of melanin production, converting tyrosine to DOPA and then to dopaquinone. When the gene coding for tyrosinase is mutated, this pathway stalls and little or no melanin is made, which is the direct cause of oculocutaneous albinism type 1.

Only tyrosinase is directly tied to the biochemical pathway that produces melanin, and its loss of function is what produces the pigment deficiency seen in albinism.

So the correct answer is Tyrosinase.