The inhibitory effects of MgCl2 on the inactivation kinetics of poliovirus by urea.

By analyzing the inhibitory effects of Mg-2+ on the three-stage urea inactivation curve of poliovirus, it was concluded that urea inactivates poliovirus via a two-step reaction as follows: urea initially converts the native virus into an intermediate state which is still infectious but is now highly sensitive to inactivation. This reaction is unaffected by Mg-2+ and is reversible. In the subsequent reaction, the sensitized virus is either irreversibly inactivated by urea or reversibly stablized by Mg-2+. In addition, the inactivation curve revealed that a fraction of relatively stable virus population was established in the presence of urea and that the size of this persistent virus population depended on the concentration of urea. It was not determined whether urea induced the formation of this stable fraction of virus or merely selected for a preexisting stable population of virus. However, evidence was presented that (1) the persistent virus population was not due to the depletion or inactivation of urea in the sample, (2) whatever stabilized the virus, it could not be removed or reversed by simple dilution as in the case of Mg-2+, (3) no excess stabilizing material was made to stabilize the addition of untreated virus and finally (4) the persistent virus population was resistant to that concentration of urea in which it was observed but could be further inactivated by a higher concentration of urea, only to result in a smaller fraction of persistent virus population.