Evidence for different Aβ40 fibril structures in brain tissue of patients I and II. (A, B) TEM images of Aβ40 fibrils, recorded 36 hr after addition of monomeric Aβ40 to sonicated extract from occipital lobe tissue of patient II. Blue arrows indicate minima in the apparent fibril diameter, associated with a periodic twist that is absent from fibril images in . Aβ40 was uniformly 15N,13C-labeled at F19, V24, G25, S26, A30, I31, L34, and M35. (C) TEM image of fibrils prepared by seeding with sonicated extract from frontal lobe tissue of patient II. (D, E) 2D 13C-13C and 15N-13C solid state NMR spectra of Aβ40 fibrils, seeded with extract from occipital lobe tissue of patient II (blue contours) or patient I (red contours). Black lines and labels show site-specific crosspeak assignments for spectra from patient II. (F, G) 2D 13C-13C and 15N-13C solid state NMR spectra of Aβ40 fibrils, seeded with extract from frontal lobe tissue of patient II, with the same black lines as in panels D and E. See also .