ALZHEIMER AMYLOID PROTEIN-PRECURSOR IS LOCALIZED IN NERVE-TERMINAL PREPARATIONS TO RAB5-CONTAINING VESICULAR ORGANELLES DISTINCT FROM THOSEIMPLICATED IN THE SYNAPTIC VESICLE PATHWAY

In order to localize amyloid protein precursor (APP) in nerve terminal s, we have immunoisolated vesicular organelles from nerve terminal pre parations using antibodies to Rab5 and synaptophysin, These immunoisol ates were then analyzed by electron microscopy and by immunoblotting. The synaptophysin immunoisolates represented a nearly homogeneous popu lation of small synaptic vesicles, with less than 10% contamination by other organelles, and very little APP. In contrast, Rab5 immunoisolat es contained, in addition to small synaptic vesicles, substantial numb ers of large uni- and bilamellar vesicles and high levels of APP. Thus , it appears that nerve terminal APP is contained predominantly in lar ge vesicular organelles, distinct from synaptic vesicles and from the synaptic vesicle recycling pathway.