The isolation of a low molecular weight serum factor which enhances the viability of sv3t3 cells

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Abstract
A serum factor which enhances the growth/viability of SV40 transformed 3T3 mouse fibroblasts, but not untransformed 3T3 cells in tissue culture has been partially purified from calf serum. The purification, which involves acidification to pH 2, chromatography on Sephadex G‐100 at pH 2 followed by either Sephadex G‐25 or BioGel P‐2, results in material exhibiting two ninhydrin positive spots on thin layer chromatography and five to six dansylatable bands on SDS gels. This substance, termed Peak III or Serum Factor III, has been found in every serum examined thus far (including calf, rat, mouse, goat, lamb, rabbit, pig, horse, and chicken) and appears to be a low molecular weight, heat‐insensitive molecule. Attempts to characterize it by chemical analyses and specific enzymatic inactivation have been either negative or inconclusive.Its biological mode of action is presently obscure. While it does not affect DNA synthesis, it does greatly increase the viability of SV3T3 cultures growing in low serum (0.15–0.30% calf serum) medium and, when added to “stationary phase” cells, restores healthy proliferation. This and evidence reported by others suggest that Peak III may affect SV3T3 cells in either overcoming a potentially lethal block in G1 or in passage through G2/M.