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Metabolite Card

Note

Dopaquinone, also known as o-dopaquinone or L-dopaquinone, is a member of the class of compounds known as L-alpha-amino acids. L-alpha-amino acids are alpha-amino acids which have the L-configuration of the alpha-carbon atom. Dopaquinone is slightly soluble (in water) and a moderately acidic compound (based on its pKa). L-Dopaquinone is a metabolite of L-DOPA and a precursor of melanin. Melanin is synthesized from tyrosine by hydroxylation to dihydroxyphenylalanine (DOPA) and subsequent oxidation to dopaquinone. Both reactions are catalyzed by the enzyme tyrosinase, which is the rate-limiting step. Dopaquinone has an ortho-quinone ring, which is known to be neurotoxic and highly reactive with many other compounds (PMID: 413870). Dopaquinone typically combines with cysteine to form pheomelanin (a pigment-polymer). Alternatively, dopaquinone can be converted to leucodopachrome and eventually to eumelanin (also a pigment-polymer). Dopaquinone can be found in skin and feces. Within the cell, dopaquinone is primarily located in the cytoplasm. Dopaquinone is involved in several metabolic disorders, some of which include transient tyrosinemia, hawkinsinuria, tyrosinemia type I, and alkaptonuria. Chronically high levels of dopaquinone are associated with Parkinson's disease (PD). Many Parkinson's patients are treated with L-DOPA. However, long-term treatment with L-DOPA may actually worsen symptoms or result in neurotic and psychotic symptoms. These may be due to dopachrome and dopaquinone accumulating in the brain of L-DOPA treated patients (PMID: 19131041, PMID: 12373519).