Dictionary of Human Evolution and Biology

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Tripeptide that is a ubiquitous constituent of all cells; several enzymatic reactions utilize glutathione as a co-enzyme. Can act to oxidize free radicals caused by UV radiation. Glutathione reductase reduces its oxidized form GSSH to GSH, the reduced form. In human skin cells, exposure to UV radiation thus temporarily lowers GSH levels (GSH → GSSH), so permitting increased activity of tyrosinase, which converts tyrosine to DOPA to dopaquinone and its eventual derivatives, eumelanin and phaeomelanin, resulting in tanning.

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