Keratins in Invertebrates

Abstract

IF the term ‘keratin’ were applied only to those proteins which contain a high proportion of cystine, which give a keratin-type of X-ray diffraction photograph and which dissolve with ease only in alkaline solutions of reducing agents, then keratins, so far as is known, are confined to the epidermis and epidermal appendages of vertebrates, and are always intracellular. Other so-called keratins from vertebrate egg capsules^1,2, byssus threads of Mytilus², etc., though they contain cystine, can be dissolved by solvents other than alkaline reducing agents, do not give a keratin-type of X-ray photograph and are extracellular structures.