摘要：

Avidin activity has been observed in the eggs as well as oviducts of many species of birds and in the egg jelly of frogs, and it has been used in the study of several different aspects of biotinyl enzymes. This chapter describes the purification and covalent chemistry, physical and binding properties, subunit structure and biosynthesis of avidin. The chapter focuses on the chemistry and binding properties of avidin. The unusually high isoelectric point of avidin and the availability of cellulose ion exchangers has led to the development of an improved procedure based on adsorption of the basic proteins on CM-cellulose at high pH, followed by elution of avidin with ammonium carbonate. The avidin–biotin complex is resistant to proteolysis by the enzymes of the digestive tract and free avidin is not inactivated by trypsin or by Pronase. Two notable features of the primary structure of avidin, both absent from streptavidin, are a single disulfide bond and an oligosaccharide linked via one of its acetylglucosamine residues to Asn. Biotinyl enzymes avidin has been used to measure changes in the availability of biotin in the presence of various ligands and to measure the binding of these ligands by the enzyme. Avidin is synthesized in the goblet cells of the epithelium of the oviduct, whereas the other major proteins of egg white are synthesized in the underlying tubular gland cells.

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