Isolation and Characterization of Intermediate Filaments

This chapter describes procedures developed for the isolation and characterization of intermediate filaments (IFs) and their subunits from different types of tissues and cells grown in culture. IFs represent one of the three major cytoskeletal components of many eukaryote cells. They appear tubular in cross section and are about 10 nm in diameter. For this reason, they are also commonly referred to as “10-nm” or “100-A^o” filaments. Their structure is unaffected by metal ions, high energy phosphates, or reductions in temperature. By both biochemical and immunological criteria, they consist of a very heterogeneous group of subunits. They can be classified into five subgroups based largely on these properties and on their tissue or cell-type of origin: those of epithelial tissues (keratin), fibroblastic cells (vimentin), muscle (desmin), astroglial cells (glial filaments), and neuronal tissues (neurofilaments). In addition, whereas microtubules and microfilaments are composed of essentially globular proteins, IFs are formed from α-helix-rich α-type fibrous proteins of the k-m-e-f class.