ABSTRACT
This chapter describes the concepts and procedures used in the isolation of a protein which is involved in a specific biological mechanism. It deals with the isolation of proteins and peptides, mainly for the purpose of structural analysis. The chapter also deals with the isolation of opioid peptides and interferons from natural sources. The interferons and the opioid peptides both comprise groups of biologically active polypeptides. Interferons are secreted by cells infected with a virus. An unusual feature of the interferon proteins is the multiplicity of forms that exist. In humans, three separate types of interferon, called alpha, beta, and gamma, are known. The beta interferon is secreted by fibroblasts into the culture medium after challenge with an infectious virus. Gamma-interferon is an extremely basic protein, and adsorbs strongly to the silica surface. The most convenient procedure for measuring interferon activity is called the cytopathic effect inhibition assay.
