Amino Acid Utilization by 929-L Fibroblasts in Chemically Defined Media2

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Abstract
A quantitative study of amino acid utilization by L cells, growing in Way-mouth's medium, MB 752/1, has been made. Glutamine, leucine, and isoleucine were exhausted when cell growth ceased. Most other amino acids were largely unused, and only about one third of the total nitrogen of the medium was incorporated into cell nitrogen. A comparison of amino acid utilization and amino acid composition of cell protein indicated that most amino acids were used in 1.5 to 2.5 times the quantities needed for protein synthesis. However, much more glutamine, more methionine and valine, and much less aspartic acid and glycine disappeared from medium than were needed for protein synthesis. The amounts of essential amino acids used by cells did not vary noticeably with amino acid composition of the medium. However, the nonessential amino acids were utilized if provided by medium, but otherwise were synthesized by cells. A modification of medium MB 752/1, which provided amino acids in the quantities consumed by cells, gave the same cell yield per volume of medium as did MB 752/1. The modified medium gave a 40 percent conversion of medium nitrogen to cell nitrogen. A medium, containing all the amino acids (except glutamine) in twice the amounts consumed by cells in MB 752/1, gave a cell yield twice that of MB 752/1, and 64 percent of the total nitrogen in the medium was incorporated into cells.