Aerobic photoreactivity of synthetic eumelanins and pheomelanins: generation of singlet oxygen and superoxide anion

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  • Grzegorz Szewczyk
    Department of Biophysics Faculty of Biochemistry, Biophysics and Biotechnology Jagiellonian University Krakow Poland
  • Andrzej Zadlo
    Department of Biophysics Faculty of Biochemistry, Biophysics and Biotechnology Jagiellonian University Krakow Poland
  • Michal Sarna
    Department of Biophysics Faculty of Biochemistry, Biophysics and Biotechnology Jagiellonian University Krakow Poland
  • Shosuke Ito
    Department of Chemistry Fujita Health University School of Health Sciences Toyoake Aichi Japan
  • Kazumasa Wakamatsu
    Department of Chemistry Fujita Health University School of Health Sciences Toyoake Aichi Japan
  • Tadeusz Sarna
    Department of Biophysics Faculty of Biochemistry, Biophysics and Biotechnology Jagiellonian University Krakow Poland

説明

<jats:title>Summary</jats:title><jats:p>In this work, we examined photoreactivity of synthetic eumelanins, formed by autooxidation of <jats:styled-content style="fixed-case">DOPA</jats:styled-content>, or enzymatic oxidation of 5,6‐dihydroxyindole‐2‐carboxylic acid and synthetic pheomelanins obtained by enzymatic oxidation of 5‐<jats:italic>S</jats:italic>‐cysteinyldopa or 1:1 mixture of <jats:styled-content style="fixed-case">DOPA</jats:styled-content> and cysteine. Electron paramagnetic resonance oximetry and spin trapping were used to measure oxygen consumption and formation of superoxide anion induced by irradiation of melanin with blue light, and time‐resolved near‐infrared luminescence was employed to determine the photoformation of singlet oxygen between 300 and 600 nm. Both superoxide anion and singlet oxygen were photogenerated by the synthetic melanins albeit with different efficiency. At 450‐nm, quantum yield of singlet oxygen was very low (~10<jats:sup>−4</jats:sup>) but it strongly increased in the <jats:styled-content style="fixed-case">UV</jats:styled-content> region. The melanins quenched singlet oxygen efficiently, indicating that photogeneration and quenching of singlet oxygen may play an important role in aerobic photochemistry of melanin pigments and could contribute to their photodegradation and photoaging.</jats:p>

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