CA2-DEPENDENT BINDING OF HUMAN SERUM AMYLOID-P COMPONENT TO ALZHEIMERS BETA-AMYLOID PEPTIDE()

Serum amyloid P component (SAP), a normal glyco protein, is universall y found in amyloid deposits, including cerebrovascular amyloid of Alzh eimer's disease. This paper describes the Ca2+-dependent binding of hu man SAP to Alzheimer's beta-amyloid peptide (A beta). I-125-SAP binds to synthetic human A beta-(1-40) immobilized on microtiter plates at a dissociation constant of 6.0 x 10(-9) M in 0.01 M Tris-HCl, 0.15 M Na Cl, pH 7.5, containing 2 mM Ca2+, 1% bovine serum albumin, and 0.05% T ween 20. Binding inhibition assay has shown that soluble A beta-(1-40) and A beta-(1-28) also bind to SAP. Since SAP is resistant to proteas es in the presence of calcium, the Ca2+-dependent binding of SAP to so luble A beta and to beta-amyloid fibrils would give pathological effec ts on fibril formation and persistence of beta-amyloid in Alzheimer's disease.