Short communication Gamma radiation interacts with melanin to alter its oxidation–reduction potential and results in electric current production Charles E. Turick a, ⁎, Amy A. Ekechukwu b , Charles E. Milliken a , Arturo Casadevall c , Ekaterina Dadachova d a Biotechnology Section, Savannah River National Laboratory, Bldg 999-W, Aiken, SC 29808, USA b Analytical Programs, Savannah River National Laboratory, Bldg 773-41A, Aiken, SC 29808, USA c Albert Einstein College of Medicine, Jack and Pearl Resnick Campus, 1300 Morris Park Avenue, Bronx, NY 10461, USA d Albert Einstein College of Medicine, Montefiore Medical Park, 1525 Blondell Avenue, Bronx, NY 10461, USA abstract article info Article history: Received 8 February 2011 Received in revised form 23 March 2011 Accepted 4 April 2011 Available online 11 May 2011 Keywords: Melanin Gamma radiation Current production Radioprotection The presence of melanin pigments in organisms is implicated in radioprotection and in some cases, enhanced growth in the presence of high levels of ionizing radiation. An understanding of this phenomenon will be useful in the design of radioprotective materials. However, the protective mechanism of microbial melanin in ionizing radiation fields has not yet been elucidated. Here we demonstrate through the electrochemical techniques of chronoamperometry, chronopotentiometry and cyclic voltammetry that microbial melanin is continuously oxidized in the presence of gamma radiation. Our findings establish that ionizing radiation interacts with melanin to alter its oxidation–reduction potential. Sustained oxidation resulted in electric current production and was most pronounced in the presence of a reductant, which extended the redox cycling capacity of melanin. This work is the first to establish that gamma radiation alters the oxidation– reduction behavior of melanin, resulting in electric current production. The significance of the work is that it provides the first step in understanding the initial interactions between melanin and ionizing radiation taking place and offers some insight for production of biomimetic radioprotective materials. Published by Elsevier B.V. 1. Introduction Melanins are complex polymers found in species of all biological kingdoms with a multifaceted utility related to physiology such as protection from visible and UV light [1,2], decreased oxidative stress [3], energy transduction and Fe(III) reduction [4–6]. However, the most fascinating and the least explored function of melanin is related to its interaction with ionizing radiation. Melanin plays a role in decreasing radiosensitivity of human melanoma cells [7] and melanized microbial species thrive in highly radioactive environments such as cooling pools of nuclear reactors, the stratosphere, space stations and inside the damaged nuclear reactor at Chernobyl [8]. Furthermore, certain melanized microbes seem to dominate the environments characterized by elevated levels of ionizing radiation such as pyomelanin-producing bacteria found in uranium-contaminated soils [9] and melanized fungi in radio-contaminated soils showing directional growth towards radiation sources (radiotrophism) [10]. Recently we demonstrated that ionizing radiation changes the electronic structure of melanin and enhances the growth of several melanized fungal species, suggesting a role for melanin in this process [11], specifically the physico-chemical interaction between melanin and ionizing radiation. Melanin pigments are diverse in structure and function in regard to effects from ionizing radiation [7,12] and offer potential as manufactured radioprotective materials [12]. Melanin pigments are composed of quinone moieties that are believed responsible for its redox behavior (Scheme 1). The polymeric structure of melanins permits oxidation and reduction to occur simultaneously. Perhaps the most interesting aspect of any radio protective material is its requirement to withstand the oxidizing impact of ionizing radiation indefinitely, without bleaching. Here we investi- gated the electrochemical response of the pigment eumelanin to ionizing radiation with a carbon paste/melanin electrode. The results establish that gamma radiation can interact with melanin thus providing key supportive evidence for the initial interactions of this pigment with electromagnetic radiation in such processes as radiosynthesis. 2. Materials and Methods 2.1. Melanin Eumelanin produced by the fungus Cryptococcus neoformans grown in presence of L-DOPA melanin precursor was used in this study. The growth of melanized cells was followed by acid hydrolysis resulting in production of hollow melanin shells dubbed “ghosts” (as they preserve the shape of the cell) was performed as in [2]. Bioelectrochemistry 82 (2011) 69–73 ⁎ Corresponding author. Tel.: + 1 803 819 8407; fax: + 1 803 819 8432. E-mail address: Charles.Turick@srnl.doe.gov (C.E. Turick). 1567-5394/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.bioelechem.2011.04.009 Contents lists available at ScienceDirect Bioelectrochemistry journal homepage: www.elsevier.com/locate/bioelechem