Pronase does not reduce the protein content of Hirt supernatant of normal mouse brain

Normal mouse brain has been used as a model in experiments to explain the reduction of infectivity obtained following incubation with Pronase of brain infected with the scrapie infective agent. Incubation of Hirt supernatants of normal mouse brain with Pronase had no effect on the protein content when compared to controls similarly incubated without Pronase. This points to a resistance of the proteins in the brain extract to protease or to the presence of anti-protease activity. Much of the 'RNA' and 'DNA' detected in the Hirt supernatant by the colorimetric procedures for these nucleic acids was alcohol soluble. The nature of the alcohol-soluble 'nucleic acid' in mouse brain and the resistance of the proteins present in Hirt supernatants to Pronase require further investigation. In experiments where Pronase reduced the infectivity of brain preparations containing the scrapie agent, the effect is probably not due to protease activity; another activity of Pronase must be involved.