PRNP and scrapie: Unlike earlier reports, in which the heparinase III treatment did not affect the conversion activity of a hamster PrPC substrate seeded with 263K hamster adapted scrapie brain homogenate [14], we show that specific depletion of endogenous heparan sulphate inhibits the conversion activity of a mouse PrPC substrate when seeded with the M1000 mouse adapted human prion strain.