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To expand the electron microscopist's options in localization and visualization, a new and general staining technique has been tested. The avidin-biotin complex serves as a coupling between the electron-dense marker, ferritin, and points of interest in biological samples. When specific cellular components are tagged with biotin, those components may be visualized with ferritin-linked avidin. Because of the remarkably strong affinity of avidin and biotin (characterized by an association constant of 10(15) M(-1)), the staining is rapid and stable. The preparation of ferritin-avidin conjugate is described, and examples are presented of the application of this complex to biotin-tagged membranes. The ghosts of Acholeplasma laidlawii have been treated with biotinyl-N-hydroxysuccinimide ester to label protein amino groups. Erythrocyte membrane oligosaccharides have been oxidized by periodate or by galactose oxidase, and the resulting aldehydes labeled with biotin hydrazide. The avidin-biotin complex in electron microscopy seems especially appropriate for seqential staining procedures, as well as for visualization of reaction sites of biotin-labeled, low-molecular-weight reagents.
Heitzmann et al. (Sun,) studied this question.