Alkaptonuria results from a deficiency of which enzyme?

Alkaptonuria is a metabolic disorder that results from a deficiency of the enzyme homogentisic acid oxidase. This enzyme is crucial in the degradation pathway of the amino acids phenylalanine and tyrosine. In individuals with alkaptonuria, the lack of homogentisic acid oxidase leads to the accumulation of homogentisic acid, which gets excreted in the urine and can also deposit in tissues, causing a condition known as ochronosis, characterized by a bluish-black discoloration of connective tissues.

The other enzymes listed are associated with different disorders. Tyrosinase is vital for melanin production and its deficiency leads to albinism. Phenylalanine hydroxylase is responsible for the conversion of phenylalanine to tyrosine, and its deficiency causes phenylketonuria (PKU). Finally, branched-chain alpha-keto acid dehydrogenase is involved in the metabolism of branched-chain amino acids, and its deficiency can lead to maple syrup urine disease. Understanding the specific role of homogentisic acid oxidase highlights the metabolic pathway involved in alkaptonuria and why its deficiency directly triggers this condition.