PHYSICOCHEMICAL PROPERTIES OF THE VIRUS PARTICLES

Relationship Between Buoyant Uensity in Caesium Chloride and Stability Between pH5 and pH7 

The remarkable difference in buoyant density between the entero- and cardioviruses (l.34g/nil) and FMUV (l.45g/nil) can best be explained by the difference in penetration of the Cs ions and subsequent reaction with the ENA. If we accept values for the density of empty capsids and ENA of I.JOg/ml and 1.91g/ml respectively we can calculate that the density of a particle containing 50% ENA and 7C% protein should be 1.48g/ml. This calculation will only be valid, however, if the ENA and protein react completely with the Os ions. Clearly the ENA in the entero- and cardioviruses must be protected from reaction with the Cs ions by its interaction with the virus protein. Even the FMUV particle has a buoyant density less than the theoretical maximiun. 

It is interesting to note, however, that the apparent density of FMUV particles increases as the time of centrifuging increase (3). Jhen this value exceeds 1.47g/ml the virus particle disintegrates. 

The stability of the virus particles below pH7 can be correlated with their density in caesium chloride. Thus the enteroviruses and cardioviruses are stable at pH3 whereas FMUV is disrupted below pH7. The rhinoviruses, which have a buoyant density of 1.40g/ml, occupy an intermediate position, being stable between pH7 and pH5 but unstable below pH5. 

FMDY is rapidly inactivated by low concentrations ( 2 ig/nil)of proflavine in the presence of visible light. This is due to inactivation of the ENA and eventually the particles disrupt into free ENA and 12S protein subimits (4) In contrast poliovirus is relatively resistant to photodynamically active dyes and any inactivation which occurs is due to oxidation of the protein coat. This observation is yet another manifestion of the porous nature of the FMDV particles compared with those of the other genera. 

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