Enzyme deficiency in Alkaptonuria is
**Core Concept**
Alkaptonuria is a rare genetic disorder characterized by the accumulation of homogentisic acid in the body due to a deficiency in the enzyme responsible for its breakdown. This enzyme is a crucial step in the catabolism of tyrosine and phenylalanine.
**Why the Correct Answer is Right**
The correct answer is the enzyme homogentisate 1,2-dioxygenase (HGD). Homogentisic acid is formed from the breakdown of tyrosine and phenylalanine, and HGD is the enzyme that catalyzes the oxidation of homogentisic acid to maleylacetoacetic acid. In Alkaptonuria, the deficiency of HGD leads to the accumulation of homogentisic acid, which is then oxidized to form melanin-like pigments in connective tissues, resulting in dark urine, ochronotic pigmentation, and other systemic complications.
**Why Each Wrong Option is Incorrect**
**Option A:** Tyrosinase - This enzyme is involved in the conversion of tyrosine to melanin, but it is not related to the breakdown of homogentisic acid.
**Option B:** Phenylalanine hydroxylase - This enzyme is involved in the conversion of phenylalanine to tyrosine, but it is not directly involved in the breakdown of homogentisic acid.
**Option C:** Aldehyde dehydrogenase - This enzyme is involved in the metabolism of various aldehydes, but it is not specifically involved in the breakdown of homogentisic acid.
**Clinical Pearl / High-Yield Fact**
Alkaptonuria is often referred to as "black urine disease" due to the characteristic dark color of the urine in affected individuals.
**Correct Answer: C. Homogentisate 1,2-dioxygenase.**