Characterization of Soluble Protein Extracts from Keratinized Tissues: Identification of Ubiquitin Universally Distributed in Hair, Nail, and Stratum Corneum

This study characterized soluble protein extracts from keratinized tissues such as hair, nail, and stratum corneum, using a method that avoided urea and surfactants. The analysis revealed low-molecular weight protein patterns distinct from whole protein extracts, which are primarily keratin. A significant finding was the identification of a major protein band, approximately 7 kDa, as ubiquitin, a protein involved in non-lysosomal protein degradation, present across all examined tissues. The study demonstrated that partial extraction methods were effective for investigating soluble proteins in keratinized tissues.