CHEMICAL AND BIOCHEMICAL CHARACTERISTICS OF TOPA QUINONE

2,4,5-Trihydroxyphenylalanine (6-hydroxydopa, abbreviated as topa) is a perhydroxylated derivative of an amino acid, tyrosine, It rarely occ urs in nature as the free amino acid, but is well known as a very stro ng neurotoxic agent, The neurotoxicity is ascribed mainly to its chemi cal reactivity and redox capacity, In addition, the oxidized form of t opa, topa quinone, has been shown to be an active non-N-methyl-D-aspar tate glutamatergic agonist and to produce neuronal cell death, Topa an d topa quinone may be biosynthesized enzymatically and non-enzymatical ly from dopa or from tyrosine through dopa, On the other hand, topa qu inone bound covalently in a protein has been identified in copper amin e oxidase, in which topa quinone serves as an essential cofactor in ca talyzing the oxidation of amines. The topa quinone cofactor is produce d by post-translational modification of a specific tyrosine precursor with the participation of the enzyme-bound copper ion, These physiolog ical and biochemical features of topa quinone as well as its chemical properties revealed by recent model studies are reviewed here.