Influence of bentonite, magnesium, and polyamines on degradation and aggregation of tobacco mosaic virus

Tobacco mosaic virus (TMV) aggregated irreversibly when incubated for 16 hours at 40° at pH 8.0 in 0.01 M MgCl2, 0.01 M bis(3-aminopropyl)amine, or 0.01 M bis(2-aminopropyl)amine. It also aggregated in salts of monovalent cations at 0.1 to 0.2 ionic strength at pH 6.5 or 8.0, but this aggregation was partly reversible. Aggregation was more rapid in some salts of monovalent cations than in others, suggesting a specific ion effect. The electrophoretic mobility was low in all buffers in which aggregation was rapid. A high surface charge may have inhibited aggregation by preventing collisions. Low concentrations of TMV degraded more rapidly in the presence of bentonite than in its absence in buffers of pH 7.0–9.0. Magnesium and polyamines inhibited the degradation. Degradation of TMV in some preparations to RNA and protein was complete at pH 8.5 in presence of bentonite and EDTA. In bentonite at pH 9.0, TMV degraded to short rods whose length depended on the Mg2+ or polyamine concentration in the range of 10−2 to 10−4 M. Rods of average length of 190 mμ that formed in bentonite and 0.0005 M MgCl2 had a full complement of RNA and 10–100% of the specific infectivity of 300 mμ rods. Excess TMV protein inhibited the aggregation of TMV under some conditions. Magnesium and polyamines had a similar effect on TMV, but differed in their reaction with chelating agents. The effect of magnesium could be counteracted by EDTA or citrate, but that of the polyamines could not.