Growth and macromolecular synthesis in the 3T6 mouse fibroblast. II. The role of serum.

Serum is necessary for growth of 3 T6 mouse fibroblasts in log phase and for their maintenance in crowded cultures, at or near the stationary phase. Removal of the dialysable components of serum has only a small effect on growth and maintenance of these cells, and has no significant effect on macromolecular synthetic processes. Fractionation of serum by ammonium sulphate precipitation did not reveal a specific association of growth-promoting activity with either of the major protein components: albumin or fetuin. The purest albumin-containing fraction, which was practically devoid of growthpromoting activity, served as a control for the physical effects of protein in the absence of serum. Omission of serum, or its replacement by albumin, caused the cells to die (i.e. disappear from the attached cell layer) at an approximately linear rate; the remainder increased in volume. Protein synthesis, including collagen synthesis, continued at a normal or enhanced rate in the remaining cells, but glucosamine incorporation was reduced.