Project Summary A new disease process – chemiexcitation – has been found to contribute to melanoma, prompting the current proposal to understand its chemistry and determine its role in additional skin disorders such as excessive scarring in burn wounds or tissue death after a temporary loss of blood supply. Chemiexcitation is the chemical excitation of an electron to a high-energy quantum state. This process underlies the bioluminescence of a firefly, but it had never been seen in mammals. Recently researchers discovered that, in the skin cells that provide skin and hair color (melanocytes), sunlight's ultraviolet radiation (UV) activates two enzymes to synthesize the free radicals nitric oxide and superoxide. These combine to form peroxynitrite, a strong oxidant that is one of the few biological molecules able to excite an electron to a high energy state. Peroxynitrite then creates a strained dioxetane ring (C–O–O–C) on fragments of melanin pigment. The ring spontaneously breaks to yield two carbonyls (C=O). One carbonyl acquires the energy – the chemiexcitation step – and ends in a quantum "triplet state" that has the energy of a UV photon but transfers this energy directly to DNA. There, the energy creates cyclobutane pyrimidine dimers (CPDs), a type of DNA damage that leads to mutations, cell death, and altered cell behavior. This process can continue for hours after a person leaves the beach, making melanin carcinogenic as well as protective. Yet inflammation and temporary blood loss can also create nitric oxide and superoxide, raising the possibility that chemiexcitation's role in disease extends well beyond sunlight and cancer. The present proposal seeks to solidify biologists' understanding of chemiexcitation events within skin and explore how the same events can be triggered without UV. The project has three aims: 1) Determine the photo-enzymatic signaling steps that initiate chemiexcitation. 2) Elucidate the unsolved biochemical steps in melanocyte chemiexcitation, seek molecules besides melanin that can host chemiexcitation, and identify genes underlying the variation in response between people. 3) Determine whether skin inflammation can substitute for UV and whether chemiexcitation therefore plays a role in hypertrophic scarring and ischemia-reperfusion injury. The results will put chemiexcitation on a firm footing in the setting of skin, and will provide a basis for investigating triplet-state energy quenchers that dissipate the high energy as heat before it can lead to disease.