Alkaptonuria is a rare inherited metabolic disorder characterized by the accumulation of homogentisic acid due to a deficiency of a specific enzyme involved in the breakdown of the amino acids phenylalanine and tyrosine.

Enzyme Deficiency in Alkaptonuria

• The disorder results from the lack of homogentisate 1,2-dioxygenase, also known as homogentisate oxidase.

• This enzyme catalyzes the conversion of homogentisic acid to maleylacetoacetate in the catabolic pathway of phenylalanine and tyrosine.

• Deficiency leads to the accumulation of homogentisic acid in the body, which is excreted in urine and deposited in connective tissues, causing characteristic symptoms.

Symptoms and Biochemical Consequences

• Darkening of urine upon exposure to air due to oxidation of homogentisic acid.

• Deposition of pigmented polymeric material (ochronosis) in cartilage and connective tissues, leading to arthritis and tissue brittleness.

• Other manifestations include dark pigmentation in sclera and skin, kidney stones, and cardiovascular complications.

Correct Enzyme from the Options

Conclusion

The inborn error of amino acid metabolism known as alkaptonuria is due to the deficiency of homogentisate oxidase (homogentisate 1,2-dioxygenase).

Correct answer: (3) Homogentisate oxidase