Chemiexcitation: Mammalian Photochemistry in the Dark.
Douglas E BrashLeticia C P GoncalvesPublished in: Photochemistry and photobiology (2023)
Light is one way to excite an electron in biology. Another is chemiexcitation, birthing a reaction product in an electronically excited state rather than exciting from the ground state. Chemiexcited molecules, as in bioluminescence, can release more energy than ATP. Excited states also allow bond rearrangements forbidden in ground states. Molecules with low-lying unoccupied orbitals, abundant in biology, are particularly susceptible. In mammals, chemiexcitation was discovered as energy transferred directly from excited melanin to DNA, creating the lethal and carcinogenic cyclobutane pyrimidine dimer. That process was initiated by nitric oxide and superoxide, radicals triggered by ultraviolet light or inflammation. Several poorly understood chronic diseases share two properties: inflammation generates those radicals across the tissue, and cells that die are those containing melanin or neuromelanin. Chemiexcitation may therefore be a pathogenic event in noise- and drug-induced deafness, Parkinson's disease, and Alzheimer's; it may prevent macular degeneration early in life but turn pathogenic later. Beneficial results of evolutionary selection for excitable biomolecules may thus have conferred an Achilles heel. This review of recent findings on chemiexcitation in mammalian cells also describes the underlying physics, biochemistry, and potential pathogenesis, with the goal of making this interdisciplinary phenomenon accessible to researchers within each field.
Keyphrases
- drug induced
- liver injury
- electron transfer
- oxidative stress
- nitric oxide
- induced apoptosis
- energy transfer
- hydrogen peroxide
- cell cycle arrest
- optical coherence tomography
- air pollution
- circulating tumor
- genome wide
- single molecule
- sensitive detection
- adverse drug
- nitric oxide synthase
- gene expression
- endoplasmic reticulum stress
- signaling pathway
- dna methylation
- human health
- climate change
- cataract surgery
- light emitting