fig5

Figure 5. Schematic diagram of melanin production. The initial stage of melanogenesis is the production of dopaquinone from L-tyrosine, catalyzed by the rate-limiting enzyme TYR. Subsequently, dopaquinone undergoes a series of redox reactions to produce dopachrome, which forms both DHI and DHICA, eventually yielding brown-black eumelanin. Notably, if cysteine or glutathione is present, the dopaquinone reacts with it to ultimately produce the reddish-yellow pheomelanin^[86]. TYR: Tyrosinase; DHI: 5,6-dihydroxyindole; DHICA: 5,6-dihydroxyindole-2-carboxylic acid; UV: ultraviolet; α-MSH: α-melanocyte-stimulating hormone; MC1R: melanocortin 1 receptor; TYRP1: tyrosinase-related protein 1; TYRP2: tyrosinase-related protein 2.