Pinacyanol as effective probe of fibrillar beta-amyloid peptide: comparative study with Congo Red.
The binding of pinacyanol (PIN), a cationic cyanine dye, to beta-amyloid fibrils (Abeta), which are associated with Alzheimer disease, was quantified by absorption spectrophotometry to measure the concentration of PIN bound to Abeta as a function of the Abeta concentration or by means of the separation of free PIN from bound PIN by centrifugation and subsequent analysis of the supernatant by visible-absorption spectrophotometry. Both methods gave equivalent results. The stoichiometry of PIN binding to Abeta was 1, and the curve representing the concentration effect of Abeta on the concentration of a dye-Abeta complex showed a biphasic curve instead of the hyperbolic curve that is characteristic of weak ligand-macromolecule interactions [e.g., as shown by Congo Red (CR)]). This and the fact that a Scatchard plot could not be fitted to the experimental data suggested that PIN binds tightly to Abeta. A comparison to the interaction of CR with Abeta led us to conclude that PIN is more sensitive than CR.
Departament de Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona, E 08028 Barcelona, Catalonia, Spain.
Raimon
R
Sabaté
Joan
J
Estelrich
D016229:Amyloid beta-Peptides / Q000032:analysis* / Q000737:chemistry; D002232:Carbocyanines / Q000032:analysis* / Q000737:chemistry; D004396:Coloring Agents / Q000032:analysis* / Q000737:chemistry; D003224:Congo Red / Q000032:analysis* / Q000737:chemistry; D015335:Molecular Probes / Q000032:analysis / Q000737:chemistry; D017433:Protein Structure, Secondary; D013053:Spectrophotometry
D016229:Amyloid beta-Peptides; D002232:Carbocyanines; D004396:Coloring Agents; D015335:Molecular Probes; D003224:Congo Red; C019071:quinaldine blue