Enzyme deficient in alkaptonuria is
**Core Concept**
Alkaptonuria is a rare genetic disorder characterized by the accumulation of homogentisic acid due to a deficiency in the enzyme responsible for its breakdown. This enzyme is a key component in the catabolic pathway of the amino acids tyrosine and phenylalanine.
**Why the Correct Answer is Right**
The correct enzyme deficient in alkaptonuria is homogentisate 1,2-dioxygenase (HGD). HGD catalyzes the conversion of homogentisic acid to 4-maleylacetoacetic acid, which is further broken down to acetoacetic acid and fumaric acid. In the absence of HGD, homogentisic acid accumulates and is eventually oxidized to benzoquinone acetic acid, leading to the characteristic symptoms of alkaptonuria, including dark urine, ochronosis, and arthropathy.
**Why Each Wrong Option is Incorrect**
**Option A:** Phenylalanine hydroxylase is the enzyme deficient in phenylketonuria, not alkaptonuria.
**Option B:** Tyrosine aminotransferase is an enzyme involved in the catabolism of tyrosine, but it is not the enzyme deficient in alkaptonuria.
**Option C:** Aldehyde oxidase is an enzyme involved in the metabolism of various compounds, but it is not the enzyme deficient in alkaptonuria.
**Clinical Pearl / High-Yield Fact**
Alkaptonuria is an autosomal recessive disorder caused by mutations in the HGD gene, which codes for the homogentisate 1,2-dioxygenase enzyme. Early diagnosis and management can help prevent the development of complications such as ochronotic arthritis and cardiovascular disease.
**Correct Answer: B. Tyrosine aminotransferase**