The Active Fraction of Rous Chicken Sarcoma,

Abstract

Recent attempts to isolate the active agent of the Rous chicken sarcoma have resulted in conflicting views as to the nature of the causative agent. Jobling and Sproul 1 - 2 have reported that repeated injections of a lipid fraction obtained from fresh or dried tumor tissue, together with nonspecific protein, produce sarcomas which appear in the more responsive birds within 3 to 4 months after the third injection. Fraenkel and Mawson, 3 on the other hand, were unable to obtain tumors by injecting acetone extracts of fresh or dried tumor tissue but were successful with the residue.

In 1936 we attempted to isolate lipid fractions from a very active preparation of Rous chicken tumor No. 1 with pentane and chloroform as solvents. With neither were we successful in producing tumors in young birds. The residue of the pentane extract, however, invariably produced tumors after a single injection in spite of 4 extractions of the powder with 100 volumes of solvent (see Table I). The residue from the chloroform extract was inactive, possibly due to denaturing the protein. The whole powder, used as a control, was very active; birds had to be sacrificed 12 days after injection. We then believed that the active fraction was not to be found among the lipids; that it was water soluble and very likely protein in nature.

In view of the recent report of Jobling and Sproul, 2 we repeated our experiments with a portion of the powder previously used. It was kept at about 5°C. for 11 months in a sealed but not evacuated tube. Pentane was used for extraction in one series of experiments; a mixture of equal volumes of chloroform and pentane in another. In each case 0.5 gm. powder was extracted 4 times with 100 volumes of solvent, taking measures that would tend to avoid denaturing the protein.