Pheomelanin Effect on UVB Radiation-Induced Oxidation/Nitration of l-Tyrosine

Abstract

Pheomelanin is a natural yellow-reddish sulfur-containing pigment derived from tyrosinase-catalyzed oxidation of tyrosine in presence of cysteine. Generally, the formation of melanin pigments is a protective response against the damaging effects of UV radiation in skin. However, pheomelanin, like other photosensitizing substances, can trigger, following exposure to UV radiation, photochemical reactions capable of modifying and damaging cellular components. The photoproperties of this natural pigment have been studied by analyzing pheomelanin effect on oxidation/nitration of tyrosine induced by UVB radiation at different pH values and in presence of iron ions. Photoproperties of pheomelanin can be modulated by various experimental conditions, ranging from the photoprotection to the triggering of potentially damaging photochemical reactions. The study of the photomodification of l-Tyrosine in the presence of the natural pigment pheomelanin has a special relevance, since this tyrosine oxidation/nitration pathway can potentially occur in vivo in tissues exposed to sunlight and play a role in the mechanisms of tissue damage induced by UV radiation.

The Multifaceted Opportunities Provided by the Pheomelanin-Inspired 1,4-Benzothiazine Chromophore: A Still-Undervalued Issue

“…As for the natural occurrence, 1,4-benzothiazines represent the main structural units of an important class of natural pigments, that is, pheomelanins [7][8][9][10][11][12][13][14], as recently demonstrated through the use of biomimetic synthetic models [15,16]. These latter ones are the yellow/reddish pigments typical of red-haired individuals of Celtic origin, biosintetically produced as a consequence of a genetically induced switch of the "normal" melanocyte activity, leading to dark photoprotective melanin pigments.…”

Electron and Photon Interactions with Bio (Related) Molecules

“…UV spectroscopy has been used to fully characterize the electronic excited states of bromopyrimidine isomers by absolute photoabsorption cross-section determination [ 16 ]. The effect of the pigment pheomelanin on UVB radiation was shown in the oxidation and nitration of tyrosine processes [ 17 ]. Moreover, enzyme activity can be controlled by treatment with coherent humid air, leading to heat inactivation.…”