Homogentisic add

Accumulation of homogentisic add in the blood causes its excretion in urine, after which it gradually darkens upon exposure to air. This sign of alcaptonuria is not present in all patients with the enzyme defidency. The dark pigment also accumulates over years in the cartilage (ochronosis), and most patients develop arthritis in adulthood. 

Conversion of Homogentisic Add lo Maleylacetoacetic, Fumarylacetoacetic, Fumaric, and Acetoacetic Acids... 

I. 13.11.27). Urinary excretion of (2-L-cystein-S-yl-l,4-dihydroxycyclohex-5-en-l-yl)acetic acid, also known as hawkinsin, and of hydroxycyclohexylacetic acid. There is mild hypertyrosinemia and acidosis. Tfeated with low protein diet and ascorbic add supplement. Defective enzyme appears to release reactive intermediates before completion of the conversion of 4-hydroxyphenylpyruvate to homogentisate (see Phenylalanine). [B.Wilcken etal. New Engl. 

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