Affordable Access

Publisher Website

Effect of pH on the oxidation pathway of dopamine catalyzed by tyrosinase

Authors
Journal
Archives of Biochemistry and Biophysics
0003-9861
Publisher
Elsevier
Publication Date
Volume
288
Issue
2
Identifiers
DOI: 10.1016/0003-9861(91)90216-6
Keywords
  • Enzyme Structure
  • Mechanisms
  • And Regulation
  • Cellular Regulation

Abstract

Abstract The oxidation of 3,4-dihydroxyphenylethylamine (dopamine) by O 2 catalyzed by tyrosinase yields 4-(2-aminoethyl) -1,2-benzoquinone ( o-dopaminequinone), which evolves nonenzymatically through two branches or sequences of reactions, whose respective operations are determined by the pH of the medium. The cyclization branch of o-dopaminequinone takes place in the entire range of pH and is the only significant branch at pH ⩾ 6. The hydroxylation branch of o-dopaminequinone only operates significantly at pH < 6, and involves the accumulation of 2,4,5-trihydroxyphenylethylamine (6-hydroxydopamine) and 5-(2-aminoethyl)-2-hydroxy-1,4-benzoquinone ( p-topaminequinone), identified from cyclic voltammetry assays. The kinetic characterization of the hydroxylation branch of o-dopaminequinone has been carried out by spectrophotometric and oxymetric assays. The successful fitting of data to the kinetic behavior predicted by the kinetic analysis at both pH ⩾ 6 and pH < 6 confirms the overall oxidation pathway proposed for the dopamine oxidation catalyzed by tyrosinase. The antitumoral power of dopamine is possibly enhanced by the high cytotoxicity of 6-hydroxydopamine and p-topaminequinone, accumulated at the acidic pH characteristic of melanosomes and melanome cells.

There are no comments yet on this publication. Be the first to share your thoughts.