Definition: Collective name for a group of proteins that form the intermediate filaments in epithelial cells. Keratins have a molecular weight between 40 kD and 68 kD and are separated one from another by electrophoresis and isoelectric focusing; thus separated, they are sequentially numbered from 1–20, and also subdivided into low, intermediate, and high molecular weight proteins. According to their isoelectric mobility they are either acidic or basic. In general, each acidic keratin protein has its basic equivalent with which it is paired to form the intermediate filaments; some keratin proteins, however, occur unpaired. Various epithelial cells contain different keratin proteins, in a tissue-specific manner. Antibodies to keratin proteins are widely used for histologic typing of tumors, and are especially useful for distinguishing carcinomas from sarcomas, lymphomas, and melanomas.
[G. keras (kerat-), horn, + -in]