Tropomyosin's end-to-end polymerization is irreversibly lost on exposure to urea or cyanate

Tropomyosin's low-salt viscosity which is due to end-to-end polymerization, is irreversibly lost upon incubation in 8M urea at room temperature. This effect is due to the chemical modification of lysine residues by cyanate in the urea. In the absence of urea, cyanate alone has the same effect. A loss in tropomyosin binding to actin accompanies the loss in viscosity, consistent with the view that tropomyosin's end-to-end interaction is necessary for strong binding to actin. During column chromatography in 8M urea, used to separate the alpha and beta chains of tropomyosin, the loss of viscosity can be minimized by using freshly-prepared urea and by reducing the time during which the protein and urea are in contact.