What is sericin protein CAS#60650-88-6 and what are its functions?
Sericin protein is a natural macromolecular protein that coats the surface of silk fibroin. Secreted primarily by the silk glands of silkworms, it is one of the major proteins forming the silkworm cocoon. Due to its excellent water solubility, ability to promote cell adhesion and proliferation, low immunogenicity, as well as its unique in situ fluorescence, antioxidant properties, and tyrosinase inhibition activity, sericin protein finds broad applications in fabric finishing coatings, cosmetic additives, food, pharmaceuticals, and functional biomaterials.
Properties of Sericin Protein
Amphoteric nature and isoelectric point
Sericin contains free hydroxyl and amino groups, which can interact to form zwitterions, giving it amphoteric properties. At lower pH values, sericin exists in a positively charged state, while at higher pH values it takes a negatively charged form. Its isoelectric point ranges between 3.8 and 4.5.Colloidal characteristics
As a macromolecular compound with a high molecular weight and particle diameter between 1–100 nm, sericin falls within the colloidal particle range. Consequently, it exhibits distinctive properties such as dialysis, coagulation, gelling, and peptization.
Denaturation behavior
When exposed to external physical or chemical factors, sericin undergoes conformational changes without altering its primary structure or breaking covalent peptide bonds. Such changes mainly manifest as variations in physical and chemical properties, loss of biological activity, and most notably, reduced solubility, which significantly limits its application value. The main causes of denaturation include temperature, pH changes, and exposure to organic solvents.
Swelling and solubility
Sericin, as a macromolecule, can absorb liquid upon contact, swell, and soften. With sufficient swelling, it eventually dissolves in the liquid. Unlike silk fibroin, which can swell but not dissolve in water, sericin dissolves readily in hot water. This property is particularly important, as it underpins processes such as silk making, scouring, and degumming.
Separation of Sericin Protein
Citric Acid Method
Sericin protein can be extracted by dissolving silk in boiling citric acid solution, since sericin is soluble in such conditions while silk fibroin remains insoluble. The dissolved sericin is then purified through dialysis and concentration. However, during dialysis, sericin often precipitates out of solution, and the resulting precipitated protein is difficult to re-dissolve.
Sodium Carbonate Method
In this method, silk is treated with an aqueous sodium carbonate solution at a controlled temperature. Under these conditions, sericin dissolves into the sodium carbonate solution, while silk fibroin stays insoluble. The insoluble fibroin is separated by filtration or centrifugation, and the sericin-containing solution is then dialyzed, concentrated, or dried to yield purified sericin protein.
