Soluble brain extracts containing 0.1 to 16 mg of
protein from 3 normal human brain and 11 patients with
Alzheimer's disease,
Down's syndrome and other
neurological disorders were assayed for
amyloid enhancing factor (AEF) activity in the mouse bioassay. At the 0.1 mg dosage, five of seven brain extracts from
amyloid-positive samples and only one of four
amyloid-negative samples demonstrated
AEF activity. Marginal
AEF activity was detected in the normal brain extracts at 8 or 16 mg
protein dosage. Alzheimer-
AEF was aggregated by exhaustive dialysis against 0.01 M
phosphate buffer, pH 6 or distilled water and the solubilized aggregate was fractionated on a BioGel P-60 column. Of the two
protein peaks,
AEF activity was present only in the low mol.wt second fraction, which on
sodium dodecyl sulfate-
polyacrylamide gel electrophoresis and
silver staining showed two discrete and three minor
peptide bands between 60 and 66 kDa and one of these was
periodic acid-Schiff positive, and three fuzzy bands near 14 kDa. Pretreatment of the crude and second fraction with 10 mM
phenylmethylsulfonyl fluoride (PMSF) nearly completely abolished the in vivo
AEF bioactivity. It is suggested that (a) a higher
AEF concentration is present in
amyloid-positive brain samples than those negative for
amyloid or normal brain tissues, (b)
AEF-positive fraction contains at least five dominant
peptides ranging between 14 to 66 kDa, and (c) abolition of PMSF-treated Alzheimer-
AEF activity, similar to that of murine
AEF, might be due to its
serine/
thiol proteinase nature. To our knowledge, this is the first time that
AEF activity has been demonstrated in Alzheimer brain samples.