Evidence against superoxide involvement in tyrosine hydroxylation by mushroom tyrosinase

Varda Kahn, Avi Golan-goldhirsh, John R. Whitaker

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

The possible involvement of superoxide anions in the hydroxylation of tyrosine by mushroom tyrosinase was studied. Superoxide dismutase and scavengers of superoxide ions of smaller MW than superoxide dismutase, such as nitroblue tetrazolium and copper salicylate, had no direct effect on the monohydroxyphenolase activity of mushroom tyrosinase. The kinetics of tyrosine hydroxylation, but not of DOPA oxidation, by mushroom tyrosinase was atrected by the addition of a xanthine-xanthine oxidase system. In the presence of the xanthine-xanthine oxidase system, the lag period of tyrosine hydroxylation was shortened compared to the lag period in the absence of the xanthine-xanthine oxidase system. The xanthine- xanthine oxidase system alone (without mushroom tyrosinase) had no effect on tyrosine conversion to dopachrome. Superoxide dismutase, catalase and hydroxyl radical scavengers counteracted to some extent the shortening of the lag period of tyrosine hydroxylation by mushroom tyrosinase caused by the xanthin e-xanthine oxidase system. It is suggested that the shortening of the lag period is due mainly to hydroxyl radicals generated by the xanthine-xanthine oxidase system via interaction of O2-. and hydrogen paroxide (a Haber-Weiss type reaction). The data do not support the direct participation of superoxide anions in tyrosine hydroxylation by mushroom tyrosinase.

Original languageEnglish
Pages (from-to)1875-1883
Number of pages9
JournalPhytochemistry
Volume22
Issue number9
DOIs
StatePublished - 1 Jan 1983
Externally publishedYes

Keywords

  • AH, reductant
  • DOPA, 3,4-dihydroxyphenylalanine
  • DTPA, diethylenetriaminepenta-acetic acid.
  • EDTA, ethylenediaminetetra-acetic acid
  • NBT, Nitroblue tetrazolium
  • O., superoxide
  • OH, hydroxyl radical
  • SOD, superoxide dismutase
  • X-oxidase, xanthine oxidase

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Plant Science
  • Horticulture

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