The Flexible Nature of the Amino Acid Pool in L Strain Fibroblasts. ∗

Abstract

Summary

Replacement of 199P medium which contins 21 ammo acids with a basal medium containing only the minimum essential ammo acids does not alter the development of a cell population in vitro, but does modify the nature of the free amino acid pool. The non-essential amino acids constitute about 80% of the intracellular pool when the cells are grown in 199P, and most of these amino acids are concentrated by the L cells. In the modified media which contain only the essential amino acids, intracellular levels of the non-essential amino acids decrease while internal levels of the essential amino acids increase. However, the cells retain a selective capacity to concentrate the non-essential amino acids, since steeper gradients for these amino acids are noted between external and internal environments. Intracellular levels of any essential amino acid can be increased by raising the level in the culture medium, but this too does not influence the development of the cell population.