Enzyme deficient in Alkaptonuria?

Ans. C. Homogentisic acid oxidase. (Ref. Harper's Illustrated Biochemistry 26 edition /pg. 255)Metabolic diseases of tyrosine catabolism include tyrosinosis, Richner-Hanhart syndrome, neonatal tyrosinemia, and alkaptonuria. Alkaptonuria The defect is tack of homogentisate oxidase. The urine darkens on exposure to air due to oxidation of excreted homogentisate. Late in the disease, there is arthritis and connective tissue pigmentation (ochronosis) due to oxidation of homogentisate to benzoquinone acetate, which polymerizes and binds to connective tissue." DiseaseDeficient enzyme1Alkaptonuria (ochronosis)Homogentisic acid oxidase2Type I, classic phenylketonuria or PKUPhenylalanine hydroxylase3HomocystinuriaCystathionine synthase4AlbinismTyrosinaseAlkaptonuria (ochronosis)# Congenital deficiency of homogentisic acid oxidase in the degradative pathway of tyrosine.# Resulting alkapton bodies cause urine to turn black on standing.# Also, the connective tissue is dark.# Benign disease, but may have debilitating arthralgias."The probable metabolic defect in type I tyrosinemia (tyrosinosis) is at fumarylacetoacetate hydrolase. Therapy employs a diet low in tyrosine and phenylalanine. Untreated acute and chronic tyrosinosis leads to death from liver failure. Alternate metabolites of tyrosine are also excreted in type II tyrosinemia (Richner-Hanhart syndrome), a defect in tyrosine aminotransferase, and in neonatal tyrosinemia, due to lowered p-hydroxyphenylpyruvate hydroxylase activity. Therapy employs a diet low in protein.