Acetonitrile-induced conformational transitions in poly-l-lysine

The effect of acetonitrile on the random coil, α-helix and β-sheet conformations induced in poly-

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-lysine is studied. It is found that acetonitrile at higher concentrations transforms the backbone of polylysine from a random coil to a helical conformation. Addition of acetonitrile to polylysine (pH 11.5) in the α-helix conformation, induces conformational changes in two stages. At concentrations below 60% v/v, acetonitrile stabilizes the helical conformation and at higher concentrations (>70% v/v), it destabilizes the helix. β-sheet→α-helix→random coil conformational transitions are found to occur when polylysine in the heat-induced conformation is titrated with acetonitrile. The possible mechanism(s) of action of acetonitrile in inducing these structural transitions is discussed.