Melanin

Lore & Background

Melanin is produced through melanogenesis, a process that begins with the oxidation of tyrosine. There are five basic types: eumelanin, pheomelanin, neuromelanin, allomelanin, and pyomelanin. Eumelanin has two forms—DHI-derived (dark, insoluble) and DHICA-derived (lighter, alkali-soluble)—which often co-polymerize. Pheomelanin contains benzothiazine units and gives red or yellow tints; it is concentrated in lips, nipples, glans of the penis, and vagina. Neuromelanin is found in the brain and binds transition metals like iron, potentially playing roles in Parkinson's disease. Allomelanin and pyomelanin are nitrogen-free forms.

Reader's Guide

Melanin is significant as the primary determinant of human skin color and provides critical photoprotection by dissipating over 99.9% of absorbed UV radiation. Its levels correlate with UV exposure in the epidermis and with age in the retina, where levels diminish 2.5-fold between the first and ninth decades of life. Studies show lower skin cancer incidence in individuals with more concentrated melanin. Research into neuromelanin investigates its efficacy in treating neurodegenerative disorders such as Parkinson's. The discovery of peptidomelanin and selenomelanin expands understanding of melanin's diversity, with selenomelanin offering potential protection against ionizing radiation for space travel.

Did You Know?

• Eumelanin can dissipate over 99.9% of absorbed UV radiation.
• Retinal melanin levels diminish 2.5-fold between the first and ninth decades of life due to oxidative degradation.
• Pheomelanin is found in many vertebrates, including fish, and its origin is not definitively tied to tetrapods.
• Selenomelanin, a selenium analogue of pheomelanin, has been synthesized and may provide better protection against ionising radiation.

Theoretical Roots of Radiosynthesis

I. Kuznetsov. He envisioned a metabolic process he called radiosynthesis, in which cells would absorb and convert the energy carried by ionizing radiation into usable chemical fuel. For decades this remained largely a speculative hypothesis, sitting on the margins of microbiology and biophysics. No one had yet identified a pigment or organism that could demonstrably perform such a conversion. The concept lay dormant until the late twentieth century, when the accidental laboratory of a nuclear disaster would provide the first tangible evidence that Kuznetsov's intuition might have been correct all along.

Fungi in the Shadow of Chernobyl

Starting in the 1990s, scientists investigating the aftermath of the disaster at the Chernobyl Nuclear Power Plant made a startling observation: roughly two hundred distinct species of fungi appeared to thrive in and around the reactor hall and the contaminated soil beyond it. What set these organisms apart was the presence of melanin, a dark pigment, embedded in their cell walls. Researchers began referring to them as radiotrophic fungi because they seemed to flourish precisely where radiation levels were extreme. A parallel pattern emerged in other harsh environments: melanized fungi were also identified in nutrient-starved, high-altitude regions where ultraviolet exposure is intense. The common thread was unmistakable—melanin-rich organisms gravitated toward, and apparently benefited from, environments saturated with energetic radiation.

Proving the Mechanism and Reaching for the Stars

Inspired by the Ukrainian findings, a team at the Albert Einstein College of Medicine of Yeshiva University in New York set out to test whether melanin could genuinely metabolize ionizing radiation. Their experiments confirmed that exposing melanin and melanized fungi to radiation boosted the pigment's capacity to drive a key metabolic reaction. Most strikingly, the fungus Cryptococcus neoformans multiplied at roughly three times its normal rate under irradiation. Microbiologist Ekaterina Dadachova, a central figure in the work, proposed a bold application: if these organisms can turn radiation into growth, they could serve as both a food supply and a source of radiation protection for interplanetary astronauts, who would face persistent exposure to cosmic rays during deep-space missions. The research reframed a humble pigment as a potential key to sustaining human life far from Earth.

Patents, Space Experiments, and Terrestrial Promise

They went further, hypothesizing that this metabolic strategy may have played a role in the earliest life on Earth, allowing melanized fungi to function as autotrophs. Back on the ground, the same organisms carry practical promise: they could offer a biological route for nuclear-waste disposal, serve as a high-altitude biofuel, or provide a novel nutrition source in extreme environments.