Heparin induction of tau isoform polymerization. 2 μM tau isoforms were mixed with various heparin concentrations (0 mg/ml to 0.024 mg/ml) and incubated 18 hrs. Polymerization was measured by (A) LLS or (B) ThS fluorescence. Symbols correspond as follows: (open square) 0N3R, (closed square) 0N4R, (open triangle) 1N3R, (closed triangle) 1N4R, (open circle) 2N3R, (closed circle) 2N4R. Data is in arbitrary units and represents an average of 3 trials ± SEM except for 2N4R with 0.006 and 0.018 mg/ml heparin, 1N4R with 0.024 mg/ml heparin, and 0N4R with 0.018 mg/ml heparin which were 2 trials. After 18 hours, heparin induced polymerization reactions were visualized by TEM at 20,000× magnification. Images are as follows: (C) 0N3R, (D) 1N3R, (E) 2N3R, (F) 0N4R, (G) 1N4R, and (H) 2N4R. Each isoform image is representative of polymerized material at 0.006 mg/ml heparin. Scale bars represent 1 μm.