The Population-dependent Requirement by Cultured Mammalian Cells for Metabolites Which They Can Synthesize: II. GLUTAMIC ACID AND GLUTAMINE; ASPARTIC ACID AND ASPARAGINE

Abstract

Abstract Cultured mammalian cells can synthesize both glutamic acid and glutamine in amounts sufficient for growth. The necessary conditions are (a) a sufficiently high population density, approaching that of a saturated culture, and (b) glutamine synthetase activity sufficiently high to utilize the newly formed glutamic acid effectively. Three strains of rat tumor cells in culture had widely varying biosynthetic capacities for asparagine, with corresponding differences in the minimum population densities permitting growth and in the precursors necessary. At extremely high population densities the 3-methyl-4-dimethylaminoazobenzene-induced carcinoma cell could grow in the absence of both aspartic acid and asparagine, the carbon skeleton then deriving from glucose and glutamine. The Jensen sarcoma cell could also synthesize aspartic acid; however, exogenous aspartic acid had to be provided in order to permit growth, the minimum effective concentration varying inversely with the population density. Although the Walker 256 cell could also synthesize aspartic acid and could transport an exogenous supply into the cell, the strain here studied would not grow under any conditions in the absence of preformed asparagine, indicative of an almost complete block in asparagine synthesis from aspartic acid and glutamine. Possible determinants of these population-dependent requirements are discussed.