5062 Benzoquinoneacetic acid Benzoquinoneacetic acid (BQA) is an oxidized form of homogentisic acid. The oxidation of homogentisic acid to BQA is catalyzed by the enzyme polyphenol oxidase. BQA is secreted in high quantities in the urine of patients suffering from cyanosis caused by vitamin C deficiency (Ella H. Fishberg, J. Biol. Chem., Jan 1948; 172: 155 - 163). Cyanosis is the bluish colouration of the skin due to the presence of deoxygenated hemoglobin in blood vessels near the skin surface. When present in sufficiently high levels, BQA can function as an osteotoxin and a renal toxin. An osteotoxin is a substance that causes damage to bones and/or joints. A renal toxin causes damage to the kidneys. Chronically high levels of BQA are associated with alkaptonuria (OMIM: 203500), an inborn error of metabolism. Alkaptonuria is a rare inherited genetic disorder in which the body cannot process the amino acids phenylalanine and tyrosine. It is caused by a mutation in the enzyme homogentisate 1,2-dioxygenase (EC 1.13.11.5), which leads to an accumulation of both homogentisic acid and BQA in the blood and tissues. When excreted in the urine, these compounds give it an unusually dark color. The accumulating BQA causes damage to cartilage (ochronosis, leading to osteoarthritis) and heart valves as well as precipitating as kidney stones and stones in other organs. More specifically, BQA can form polymers that resemble the dark skin pigment melanin. These are deposited in collagen, especially in tissues such as cartilage. This process is called ochronosis (as the tissue looks ochre); ochronotic tissue is stiffened and unusually brittle, impairing its normal function and causing damage. 10275-07-7 C8H6O4 2018-03-21T18:00:09Z 2018-03-21T18:07:51Z true OC(=O)CC1=CC(=O)C=CC1=O C8H6O4 InChI=1S/C8H6O4/c9-6-1-2-7(10)5(3-6)4-8(11)12/h1-3H,4H2,(H,11,12) RAPRJRLALQKSHB-UHFFFAOYSA-N 166.1308 166.02660868 HMDB0002334