Question

Which of the following enzymes is absent in a person suffering from Alkaptonuria?

• A. Tyrosinase
• B. Homogentisic acid oxidase
• C. Catechol dioxygenase
• D. Phenylalanine hydroxylase

Answer 1

The Correct Option is B

Alkaptonuria is a rare metabolic disorder characterized by the accumulation of homogentisic acid. This occurs due to a deficiency in the enzyme that is responsible for breaking down homogentisic acid.

Let's go through the provided options one by one to determine which enzyme is absent in individuals with Alkaptonuria:

1. Tyrosinase: This enzyme is involved in the production of melanin from tyrosine and is not related to the breakdown of homogentisic acid. Therefore, the absence of tyrosinase is not responsible for Alkaptonuria.
2. Homogentisic acid oxidase: This enzyme is crucial in the metabolic pathway of tyrosine degradation. Its primary role is to catalyze the conversion of homogentisic acid into maleylacetoacetic acid. In individuals with Alkaptonuria, the deficiency of homogentisic acid oxidase leads to the accumulation of homogentisic acid, causing the characteristic symptoms of the disorder. Thus, the absence of homogentisic acid oxidase is responsible for Alkaptonuria.
3. Catechol dioxygenase: This enzyme is involved in the breakdown of catechol and unrelated to the metabolism of homogentisic acid. Hence, its absence does not cause Alkaptonuria.
4. Phenylalanine hydroxylase: This enzyme converts phenylalanine to tyrosine and is involved in a different metabolic pathway. Its deficiency leads to a condition known as Phenylketonuria (PKU), not Alkaptonuria.

Based on the above analysis, the correct answer is:

• Homogentisic acid oxidase.

Thus, in Alkaptonuria, the enzyme that is absent and leads to the accumulation of homogentisic acid is homogentisic acid oxidase.