Demonstration of tyrosinase in the vitiligo skin of human beings by a sensitive fluorometric method as well as by 14C(U)-L-tyrosine incorporation into melanin

J Invest Dermatol. 1982 Mar;78(3):243-52. doi: 10.1111/1523-1747.ep12506603.

Abstract

Tyrosinase activity (Monophenol, dihydroxyphenylalanine: oxygen oxidoreductase EC 1.14.18.1) in vitiligo and normal epidermal homogenates of skin from human beings was measured by estimating beta 3,4-dihydroxyphenylalanine (dopa) by a highly sensitive fluorometric method described in this paper. The tyrosine activity in the vitiligo skin was about 4 to 37% of corresponding normal skin. The activity of tyrosinase in normal human skin from different individuals and from different regions of the body was in the range of 4 to 140 picomoles of beta 3,4-dihydroxyphenylalanine formed per min/mg protein of epidermal homogenate. The enzyme from vitiligo and normal skin was severely inhibited by substance(s) of low molecular weight. The enzyme exhibits a lag of about 4 hr in the absence of added beta 3,4-dihydroxyphenylalanine and 1 hr in presence of 5 microM dopa. Tyrosinase from the normal and vitiligo skin was inhibited by excess concentration of tyrosine. The homogenates from vitiligo skin could synthesize melanin from C14(U)-L-Tyrosine. The rate of tyrosine incorporation into melanin by the epidermal homogenates is increased by 3,4-dihydroxyphenylalanine (dopa) disproportionate to its effect on tyrosinase activity. Based on the data presented in this paper it is concluded that melanocytes are present in the vitiligo skin. A tentative hypothesis is put forward to explain the lack of melanin synthesis by the vitiligo skin under in vivo conditions, although melanocytes are present.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cadaver
  • Carbon Radioisotopes
  • Catechol Oxidase / analysis*
  • Culture Techniques
  • Dihydroxyphenylalanine / biosynthesis
  • Humans
  • Hydroxylation
  • Melanins / biosynthesis
  • Monophenol Monooxygenase / analysis*
  • Monophenol Monooxygenase / metabolism
  • Skin / enzymology*
  • Spectrometry, Fluorescence / methods
  • Tyrosine / metabolism
  • Vitiligo / enzymology*

Substances

  • Carbon Radioisotopes
  • Melanins
  • Tyrosine
  • Dihydroxyphenylalanine
  • Catechol Oxidase
  • Monophenol Monooxygenase