L-Cystine, with the CAS number 56-89-3, is a naturally occurring sulfur-containing amino acid, also known as (R,R)-3,3′-Dithiobis(2-aminopropanoic acid). Its molecular formula is C₆H₁₂N₂O₄S₂, and its molecular weight is 240.30 g/mol. It is formed by the oxidation of two L-cysteine molecules linked by a disulfide bond, serving as an essential component of proteins and playing a crucial role in maintaining biological structure and function. Due to its unique sulfur-containing structure and excellent biocompatibility, it is widely applied in pharmaceuticals, food supplements, cosmetics, and biochemistry research fields.
Physically, L-Cystine appears as a white to off-white crystalline powder or needle-like crystals. It has a melting point of approximately 260-261℃ (decomposition) and is slightly soluble in cold water, more soluble in hot water and dilute acids, and slightly soluble in ethanol, while insoluble in non-polar solvents. It is optically active, with a specific rotation [α]²⁰/D of -215° to -225° (in 1 mol/L hydrochloric acid, c=1). It has low hygroscopicity and remains stable under normal temperature and pressure when stored properly, facilitating easy handling, storage, and formulation.
Chemically, the disulfide bond is its core functional group, which is essential for stabilizing protein tertiary structures by forming cross-links between polypeptide chains. It can be reduced to two L-cysteine molecules under reducing conditions, and oxidized back to L-cystine under oxidative environments, participating in the body’s redox balance. It also contains two amino groups and two carboxyl groups, enabling it to participate in peptide bond formation and various biochemical reactions.
Its core applications cover multiple fields. In the pharmaceutical industry, it serves as a raw material for preparing amino acid supplements, drugs for treating cystine deficiency, and liver-protective agents, as it helps maintain the body’s sulfur balance and supports cellular metabolism. In food supplements, it is added to health products to enhance immunity, promote hair, skin, and nail health, and support antioxidant defense.
In cosmetics, it is incorporated into skin care products to nourish the skin, improve skin elasticity, and inhibit melanin formation, contributing to a bright and smooth complexion. In biochemistry research, it is used as a biochemical reagent for studying protein structure, redox reactions, and amino acid metabolism. Safety-wise, it is generally recognized as safe (GRAS), non-toxic and non-irritating under normal handling. It should be stored in a sealed, cool, dry, and dark environment, away from oxidants, moisture, and high temperatures to prevent oxidation and degradation. With its essential physiological functions and versatile applications, it is an important raw material in multiple high-value industries.
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