Research on substances inactivating the X virus present in sap from potato leaves

The work ofJermoljev andBr?ák (1964) showed that the sap of potato leaves contains substances inactivating X, Y and S viruses and that there was an increasing trend in the content of these substances in varieties resistant to these viruses. In further research it was found that potato tubers of varieties which are resistant and susceptible to the viruses contained the same amounts of inactivating substances. Differences in the power of inactivating the viruses evidently appeared in the leaves. Inactivating substances could be removed by boiling, they did not pass through a dialysing membrane and were adsorbed by animal charcoal. On centrifuging sap from potato leaves in a Spinco L ultracentrifuge for 60 min. at 40,000 r.p.m., the inactivating substances remained in the supernatant. When sucrose gradient centrifugation for 60 min. at 24,000 r.p.m. was employed, the inactivating substances remained in the layer of sap and 10% sucrose. Inhibition of the activity of certain enzyme groups did not affect the power of sap to inactivate X virus. Inactivating substances could be isolated chemically. The best method of isolation, however, was fractionation of sap, after ultracentrifugation, on a Sephadex G 50 column, rinsing the column with McIlvaine buffer at pH 6·5. Inactivating substances can be isolated, concentrated and preserved by lyophilization by this method. It is difficult to say precisely to what chemical group the inactivating substances belong. Some reactions indicate that they may be low molecular proteins.