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.
In one experiment, they found that gamma rays induced a four-fold increase in melanin’s ability to catalyze an oxidation-reduction reaction typical of cell metabolism. They also tested melanin’s response to gamma rays using electron spin resonance, a technique similar to nuclear magnetic resonance spectroscopy. Gammarays changed the distribution of unpaired electrons in the molecule, says Casadevall’s Albert Einstein colleague Ekaterina Dadachova. These findings suggest that gamma rays kick some melanin electrons into excited states, initiating a yet-unknown process that would end up producing chemical energy, Casadevall says. This might be similar to the way in which photosynthesis supplies energy to plants, he adds. He speculates that melanin might collect energy not only from gamma rays but also from lower-energy radiation such as X rays or ultraviolet rays. “I think this is only the tip of the iceberg,” he says. (Source)