Disaggregating effects of ethanol at low concentration on beta-poly-L-lysines

Protein aggregation is involved in a number of disorders, such as Alzheimer's disease, cystic fibrosis, and prion diseases. Such aggregates are formed by peptides in beta-conformation. The study of the processes of aggregation or its inhibition makes it necessary for the peptide to remain in a monomeric state at the beginning of aggregation assays. Using three poly-L-lysine as a model of beta-peptide, we measured the spectral changes occurring in the visible spectrum of Congo Red (CR), a diazo dye, in two solvent media, namely, an aqueous solution of ethanol 10% (v/v), and an aqueous solution of dimethyl sulfoxide (DMSO) 5% (v/v). Aggregation constants show that the presence of ethanol at low concentration produces a disaggregating effect, regardless of the degree of polymerisation of the peptide. This effect is considered to be due to the direct binding of ethanol molecules to the peptide. This binding undergoes an enhancement of the electrostatic repulsion among charged lysine chains.