Stoichiometry of F 1 - Avidin - BHMM Complex

In the course of studies on the ultrastructural localization and functions of contractile proteins in nonmuscle cells, we have found it useful to adapt the avidin-biotin complex technique introduced by Hei tzmann and Richards (7) to the specific labeling of actin and myosin components in these cells. These authors modified cell surfaces by covalent attachment of biotinyl residues, and then visualized these residues in electron microscopy by staining with a ferritin-avidin conjugate, thereby making use of the extraordinarily high binding affinity of biotin for avidin (5). We have used this general procedure to develop two specific fluorescence staining procedures, one for intracellular actin, the other for myosin. The actin procedure involves the successive reaction with biotin-labeled heavy meromyosin (HMM) followed by fluorescein-labeled avidin, which in our hands has given results superior to those obtained with the use of direct fluorescein-labeled HMM as described by Sanger (11). The myosin labeling procedure involves the successive reaction with biotin-labeled antimyosin antibody followed by fluorescein-labeled avidin, which provides an alternative and comparably effective staining procedure to the usual indirect immunofluorescence technique.