6,8-Dihydroxypurine: a novel growth factor for mammalian cells in vitro, isolated from a commercial peptone

A substance promoting the growth of mammalian cells in vitro has been isolated from Bacto-peptone (Difco Labs., Detroit) and identified as 6,8-dihydroxypurine. This compound, which is isomeric with xanthine(2,6-dihydroxypurine), enhances the growth of one Chinese hamster and some other cell lines; xanthine itself is inactive. The biological action of the compound is discussed.