Solvent effect on aggregational properties of β-amyloid polypeptides studied by FT-IR spectroscopy

Aggregation of the beta-amyloid peptides is the major hallmark of the brain in case of Alzheimer's disease. On the basis of some results it is assumed that the toxic centrum of the beta A4 (1-42) amyloid peptide is primarily the (31-35) fragment [N.W. Kowall, A.C. McKee, B.A. Yanker, M.P. Beal, Neurobiol. Aging 13 537-542; B. Penke, L. Toth, K. Soos, J. Varga, E.Z. Szabo, J. Marki-Zay, A. Baranyi, in: H.L.S. Maia (Ed.), Peptides 1994, Proceedings of the 23rd European Peptide Symposium Escom, Leiden, 1995, pp. 101-102; I. Laczko, Z. Konya, J. Varga, K. Soos, M. Hollosi, B. Penke, in: H.L.S. Maia (Ed.), Peptides 1994, Proceedings of the 23rd European Peptide Symposium Escom, Leiden, 1995, pp. 549-550]. Two analogues of beta A4 (1-42) were synthetized: one of them includes the toxic fragment (31-35) unchanged and consists mainly of hydrophilic residues, denoted as MOD-3. The other one does not contain the toxic fragment and has mainly hydrophobic residues, denoted as MOD-4. Peptides were dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol to have deaggregated samples. After the addition of the D2O as second solvent, the aggregation was followed by FT-IR spectroscopy. Changes of the spectra as a function of the composition of the solvent mixtures will be shown and discussed. Based on the results, FT-IR spectroscopy seems to be a suitable analytical control in standardizing the aggregation grade of beta-amyloid peptides. (C) 1999 Elsevier Science B.V. All rights reserved.