Question

Blackening of urine occurs when exposed to air, is a metabolic disorder in human beings. This is due to

• A. Phenylalanine
• B. Tyrosine
• C. Valine replacing glutamine
• D. Glutamine replacing valine
• E. Homogentisic acid

Answer 1

Answer: (E)

Homogentisic acid

Alkaptonuria or ochronosis is a rare inherited metabolic disorder caused by the defects in homogentisic acid oxidase enzyme-producing gene. Homogentisic acid is the degradation product of tyrosine and phenylalanine. This is broken down further to maleylaceticacid by the enzyme homogentisic acid oxidase. This genetic defect causes homogentisic acid to be excreted in the urine. The homogentisic acid in urine turns black when exposed to air.

So, the correct answer is option E.