Question

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

• A. Phenylalanine
• B. Tyrosine
• C. Valine replacing glutamine
• D. Homogentistic acid
• E. Glumine replacing valine

Answer 1

The correct option is D Homogentistic acid

Alkaptonuria is an inherited condition that causes urine to turn black when exposed to air. Mutations in the HGD gene cause alkaptonuria. Homogentisic acid, which is produced when phenylalanine and tyrosine are broken down, accumulates in the body. Excess homogentisic acid is deposited in connective tissues, which causes cartilage and skin to darken. Over time, a buildup of this substance in the joints leads to arthritis. Homogentisic acid is also excreted in urine, making the urine turn dark when exposed to air.