Keratin is an insoluble protein that is the major constituent of the outer layer of the skin, nails, and hair. It contains greater amounts of amino acid called cystine.
Generalic, Eni. "Keratin." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. 1 Apr. 2025. <https://glossary.periodni.com>.
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