Nucleoside diphosphatase (NDPase) activity associated with human beta-protein amyloid fibers.

Nucleoside diphosphatase (NDPase) activity was studied by electron microscope cytochemistry in surgical specimens obtained from aged human cerebral cortices. The presence of NDPase activity on the surface of the microglial cells (MCs) and especially within the endoplasmic reticulum (ER) cisternae that are filled with amyloid fibers and that are in continuity with the extracellular amyloid deposits in plaques suggests a possible role of this enzyme in final elaboration of amyloid protein. The close structural relationship between MCs and amyloid plaques, suggesting the participation of these cells in the synthesis or final elaboration of amyloid fibers, was observed. The comparison of these observations with previously reported data on the distribution of NDPase in MCs and amyloid fibers in scrapie-infected mouse brain suggests that presumably similar mechanisms are acting in both cases. These observations, as compared with the results of other cytochemical and biochemical studies, also suggest that co-localization of NDPase activity with newly formed amyloid fibers in plaques can be associated with glycosyltransferase activities engaged in the amyloid or amyloid precursor protein glycosylation.