Ubiquitin-protein conjugates in Alzheimer's lesions.

The ubiquitin-dependent protein degradation system plays a major role in the removal of abnormal and denatured proteins which may form insoluble aggregates in pathological conditions or during other cellular stress. Neuritic plaques and neurofibrillary tangles in sections of Alzheimer's cortex contain insoluble aggregates of proteins and are shown here to specifically immunostain with an antiserum to ubiquitin-protein conjugates. Plaque core amyloid and normal neurons do not immunostain and sodium dodecyl sulphate (SDS)-insoluble tangle preparations are not ubiquitin-positive on slot blots. The possible role and consequences of ubiquitination in tangle and plaque production in Alzheimer's disease are discussed.