Calcium ion binding by isolated tobacco mosaic virus coat protein

Calcium ion titrations were performed on solutions of tobacco mosaic virus coat protein using a calcium-specific ion-exchange electrode. Isolated coat protein was found incapable of binding calcium ions under equilibrium conditions at pH values above its iso-ionic point (pH 4·3 to 4·6). However, calcium ions were found to bind to coat protein under non-equilibrium conditions, which suggests that the isolated coat protein has the proper conformation to bind calcium ions at the iso-ionic point.