Paired helical filaments are not the major binding sites for wheat germ and Dolichos biflorus agglutinins in the neurofibrillary tangles of Alzheimer's disease

The isolated paired helical filaments (PHF) that occur in the neurofibrillary tangles of Alzheimer's disease were assayed to determine if they contained N-acetyl-glucosamine and N-acetyl-galactosamine residues. The enzyme-linked lectin assay was used to detect their total content in the PHF preparation. The assay employed biotinylated Dolichos biflorus and wheat germ agglutinins and was developed with avidin-horseradish peroxidase. The total PHF preparation was shown to contain very little of these glycosylated control proteins. Colloidal gold-labeled lectins were used to study the PHF by electron microscopy to assess whether the minor amount of lectin binding in the total preparation was directly associated with the PHF. These studies showed no significant association of the colloidal gold-labeled lectins with the isolated filaments. We conclude that the PHF themselves contain few or no N-acetyl-glucosamine or N-acetyl-galactosamine residues.