When it comes to melanin, melanocytes are mentioned. Melanocytes are dendritic and are located at the bottom of the skin. They synthesize and secrete melanin. Melanosome is a specific organelle in melanocytes. Melanin is synthesized in the black body and finally released by exocytosis.
Melanin is a high molecular polymer, which is divided into brown-black insoluble melanin and red-yellow sulfur-soluble soluble brown melanin. The interaction of two melanin is the reason why different people have different skin tones.
Melanin absorbs and scatters ultraviolet light and protects the skin from ultraviolet radiation (UVR), thereby protecting intracellular DNA. However, when the melanin is excessively deposited, the skin color is dull, affecting the appearance, and even causing an increase in pigmentation.
The melanin synthesis process refers to a process in which L-tyrosine undergoes a series of enzymatic reactions to oxidize to form melanin and brown melanin in an environment containing or not containing cysteine.
Stacey believes that L-phenylalanine in cell fluid is converted to L-tyrosine by phenylalanine hydroxylase (PAH) catalysis, and the catalysis of L-tyrosine in tyrosinase (TYR) Under hydroxylation to form dopa, dopa is then oxidized to dopaquinone under the catalysis of TYR.
If cysteine or glutathione is present in the internal environment, dopaquine reacts with it to form cysteine dopa, eventually forming red/yellow brown melanin;
If cysteine or glutathione is absent, dopaquinone spontaneously cyclizes to form dopachrome. When tyrosine-related protein-2 (TRP2) is absent in the body, dopachrome spontaneously changes to 5,6-dihydroxyindole (DHI); when TRP2 is present, dopachrome is mutually mutated under its catalytic action. The structure is 5,6-dihydroxyindolecarboxylic acid (DHICA), and tyrosine-related protein-1 (TRP1) is oxidized to form brown/black melanin.
Stacey mentioned in the article that tyrosinase is the most important key enzyme in melanin synthesis, and inhibiting the activity of this enzyme can reduce the rate and quantity of melanin synthesis.