The Avidin-Biotin Complex in Affinity Cytochemistry

This chapter describes the avidin–biotin complex in affinity cytochemistry. The use of affinity methods for the localization, visualization, and subsequent evaluation of specific cellular components is termed “affinity cytochemistry.” In general, the technique is based upon the preparation of a mixed conjugate, comprising a biologically active molecule attached chemically to a potentially perceptible probe, whereby the resultant product retains both detectability and biological activity. A wide spectrum of biologically active molecules is coupled to the above probes, including antibodies. The use of the high-affinity avidin–biotin complex is shown to circumvent some of the problems relating to ferritin–protein conjugation. In addition, this method is employed to unify and facilitate certain aspects of affinity cytochemical techniques. There are numerous steps involved in this step, such as biotin is attached via an appropriate reactive derivative either directly to cell surface functional groups or to a biologically active molecule. The preparation of ferritin–avidin conjugates is described in the chapter.