Fibrillar amyloid beta-protein forms a membrane-like hydrophobic domain

Microviscosity of the biological membranes is determined by measuring the f luorescence polarization of diphenylhexatriene (DPH). DPH, a hydrophobic pr obe, has negligible fluorescence in the solution. When DPH is incorporated into the membrane, it is localized in the membrane hydrophobic core and flu oresces strongly. We report here that DPH also fluoresces in the presence o f fibrillar A beta (fA beta). However, it does not fluoresce when it is add ed to the soluble A beta (sA beta). DPH Inserts into A beta fibrils in a ti me-dependent manner, and upon centrifugation, it is sedimented along with f ibrils. The steady state fluorescence polarization of DPH with fA beta1-40 and fA beta1-42 was 0.4592 and 0.4898 respectively. These results suggest t hat fA beta (but not sA beta) forms a hydrophobic domain similar to that of membrane. NeuroReport 12:587-590 (C) 2001 Lippincott Williams & Wilkins.