Melatonin-AFMK-AMK Cascade as GSH-Independent Thermal Antioxidant Buffer

Corals are extraordinary animals that survive by hosting tiny algae inside their cells — these algae photosynthesize and feed the coral in exchange for shelter. But when ocean temperatures spike, this partnership breaks down catastrophically in a process called coral bleaching: the algae get expelled, the coral turns white, and if the heat persists, it dies. One key reason this happens is oxidative stress — heat causes a surge of damaging molecules called free radicals, and the coral's main chemical defense, a molecule called glutathione (GSH), gets overwhelmed and crashes. This hypothesis proposes that melatonin — yes, the same hormone humans use for sleep — might offer a backup defense system. Melatonin is actually a powerful antioxidant found in both animals and plants, and when it neutralizes free radicals, it doesn't just disappear. It breaks down through a chain of chemical reactions into related molecules called AFMK and then AMK, each of which can keep neutralizing more free radicals. The idea here is that this melatonin cascade could act as a kind of 'Plan B' antioxidant buffer — one that doesn't rely on glutathione at all — kicking in precisely when the primary defense system collapses under thermal stress. The bridge between plant stress biology and coral biology is clever: plants under heat stress use similar melatonin-based defenses, and the symbiotic algae living inside corals are essentially plant-like organisms. This is a speculative but chemically plausible idea. If the melatonin-to-AFMK-to-AMK cascade is active in thermally stressed coral cells, it could represent an underappreciated survival mechanism — and potentially an exploitable one.

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