Role of fatty acids in growth‐promoting effect of serum albumin on hamster cells in vitro

Dialyzed serum albumin had considerable growth‐promoting effect on cultivated hamster cells. This effect was virtually lost on removal of the fatty acids, and it was completely restored by recombination of the fatty acid‐free albumin with the isolated and purified fatty acids. The role of albumin itself appeared to be largely that of a carrier of fatty acids, protecting the cells against toxic effects of fatty acids in free solution. This conclusion was based on two observations: Fatty acids in the absence of albumin were growth‐inhibitory except in extremely dilute solutions, and betalactoglobulin, a protein possessing, like albumin, the ability to bind and release fatty acids, could replace albumin in the presence of fatty acids with similar growth‐promoting effect. Examination of individual molecular types of fatty acids showed that all unsaturated acids tested were growth‐promoting, whereas the saturated acids were growth‐inhibiting, with the exception of stearic acid in low concentrations. Although the possibility of a mitotic triggering effect was not excluded, the fatty acids presumably stimulated growth by providing substrate for cellular metabolism, since there was a direct relationship between the degree of growth stimulation and the duration of exposure of cells to the fatty acids.