CATION BINDING BY PAPAYA MOSAIC-VIRUS AND ITS PROTEIN

Hydrogen-ion titration curves of papaya mosaic virus and its protein, with or without added CaCl2 or MgCl2 are presented and analysed. The virus particle contains three cation-binding sites per subunit, half protonated at pH values of 5.6, 7.0, and 8.6, respectively. Long protein rods, which are stable below pH 7, probably contain two cation-binding sites per subunit, while more dissociated protein probably contains only one. We calculate that the electric charge on the virus will be almost zero, and almost independent of pH, in biological fluids containing significant amounts of divalent cations. © 1979.