Gamma radiation interacts with melanin to alter its oxidation–reduction potential and results in electric current production

Abstract

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 oxidationreduction 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.

Synthesis and assembly of fungal melanin

“…Experimental evidence suggests that fungal melanin can convert the energy of radiation to metabolically useful reducing power (Dadachova et al 2007). Additional support for this notion comes from the observation that irradiation of a melanin electrode with gamma rays resulted in the formation of an electric current, thus indicating the potential for this interaction to result in energy transduction (Turick et al 2011). …”

Polyextremotolerant black fungi: oligotrophism, adaptive potential, and a link to lichen symbioses

“…Metabolic responses of melanin-producing fungi to ionizing radiation include increasing rates of electron transfer, measured as reduction of ferricyanide by the reduced nicotinamide adenine dinucleotide (NADH) (Dadachova et al, 2007). Gamma radiation-induced oxidation of melanin resulted in electric current production, especially in the presence of a reducing agent (Turick et al, 2011). The biological significance of this phenomenon is still unclear and some experiments yield contradicting results: gamma radiation, UV, and visible light seem to cause a reduction of ATP levels in melanized cells of the fungus Cryptococcus neoformans (Bryan et al, 2011).…”

Compton Scattering by Internal Shields Based on Melanin-Containing Mushrooms Provides Protection of Gastrointestinal Tract from Ionizing Radiation

“…1 Many fungi, such as human pathogen Aspergillos niger, are black due to melanin presence, but the pigment is widespread among the edible fungi (mushrooms) as well. There are two major classes of melaninmelanins that do not contain sulfur in their structure are called eumelanins, while melanins which incorporate divalent Departments of 1 Radiology, 4 Physiology and Biophysics, 5 Medicine, 6 Pathology, sulfur are called pheomelanins 2 ( Fig. 1A, B).…”

“…Initially, we demonstrated that microbial melanin could function in transducing the energy of c radiation in fungal cells 3 and that the efficacy of the radioprotection of melanized cells by melanin was dependent on its chemical composition and spatial arrangement. 4 The observation that c irradiation of melanin caused changes in melanin chemical structure, paramagnetism, 5 reversible oxidation, and electrical current production 6 provided direct evidence for the ability of c radiation and melanin to interact. In addition to free reactive radical scavenging, radioprotection by melanin involved gradual energy dissipation of Compton recoil electrons through their interaction with the p-electron-rich melanin structural units until the kinetic energy of recoil electrons becomes low enough to be trapped by stable free radicals present in the pigment.…”