Solid phase assay studies on the interaction of tauPRD with F-actin. 50 μl skeletal muscle F-actin (5 μg/ml) was added to solid phase assay wells. Aliquots of different concentrations of tauPRD (○), tau (□) and tauMTBD (△) were incubated with actin in binding buffer. Immunoreactivity was monitored using secondary antibody-labelled HRP. Each point represents the mean of five determinations. Binding parameters were estimated by fitting data using the Hyperbl function in Origin (Table 2).