Biochemistry of Amino Acids - A. Meister 1961

The Role of Amino Acids in Nutrition
Amino Acid Requirements of Cells Grown in Tissue Culture

Until recently, Cell cultivation in tissue culture was carried out using complex media of undefined composition. Fischer and co-workers [100–102] successfully demonstrated the relative requirement of chick embryo myeloblasts for A number of Amino Acids (glutamine, Arginine, cystine, Tryptophan, Histidine, Proline) as growth stimulants. They also established that glutamine is essential for the growth of mammalian Cells in tissue culture [101]. Eagle [103, 104] developed a tissue culture method that makes it possible to determine the requirement of cells for individual amino acids (and Other Compounds). Thus, it became possible to cultivate mammalian cells (including human carcinoma cells) in media consisting predominantly of known chemical components. The COMPOSITION OF THE basal medium used in these studies is given in Table 13. In addition to the listed components, a small amount of dialyzed Blood serum must be added to the medium. However, serum apparently does not play The Role of an amino acid source here. Both mouse fibroblasts and human Cancer cells require the presence of 13 L-amino acids for growth; the corresponding D-isomers are inactive. The simultaneous requirement for cystine and Methionine indicates that these cells are incapable of converting methionine into cystine at a rate meeting growth demands. A similar Conclusion can be drawn regarding The conversion of phenylalanine to Tyrosine. The requirement for glutamine is of particular interest, since in the intact mouse or human Organism this amino acid is not essential for growth and the maintenance of nitrogen balance. For mouse fibroblasts, glutamic acid does not replace glutamine, even upon The addition of ammonium ions and adenosine triphosphate. Glutamic acid slightly enhances the growth of human cancer cells, but much less effectively than glutamine. Obviously, under these conditions, the ability of these cells to synthesize glutamine is limited; in this respect, they resemble certain microorganisms that also exhibit a relative requirement for glutamine (p. 318). Several days after the exclusion of any essential amino acid from the medium, the cells become damaged and soon die. Upon the timely addition of the corresponding amino acid, cell growth rapidly resumes.

Class="center">Table 13 Composition of the basal medium for the cultivation of human carcinoma cells (HeLa) and mouse fibroblasts (103)

Cells grown in tissue culture may lose the capacity for a number of metabolic conversions. It is quite probable, however, that only certain Types of Animal cells carry out such reactions as the Synthesis of Glutamine or the conversion of phenylalanine to tyrosine. Apparently, glutamine is synthesized in specific cells and transported to others via the bloodstream. Interestingly, the minimum concentration of glutamine required for optimal growth of tissue cultures is significantly higher than the required concentrations of Other Amino Acids. The amount of glutamine in the blood also considerably exceeds the content of other amino acids (Table 3).

Evans and co-workers [105, 106] cultivated mouse fibroblasts (strain L-929) in a chemically defined medium devoid of protein. This medium included 25 amino acids (including the 13 amino acids used by Eagle), as well as a number of other compounds (e.g., Inositol, vitamin A, p-aminobenzoate, diphosphopyridine nucleotide, deoxyguanosine); it has not yet been established whether all these compounds are necessary for the growth and survival of these cells. A similar medium was proposed by Healy and co-workers [107].