The amino acid requirements of rabbit fibroblasts, strain RM3-56.

Strain RM3-56 of rabbit fibroblasts was found to require arginine, cystine, glutamine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, serine, threonine, tryptophan, tyrosine, and valine for growth in a medium containing 2 per cent dialyzed serum as the only undefined component. The requirement for serine is less specific than that of the other 13 amino acids and it is partially replaced by glycine, or alanine, or by several combinations of so called accessory amino acids. The concentrations of essential amino acids which permit maximal proliferation range from 0.005 to 0.3 mM. Cystine, glutamine, lysine, tryptophan, tyrosine, valine are toxic at concentrations of 5 mM. The rate of proliferation of RM3-56 in a medium containing all 14 essential amino acids is increased significantly by the addition of alanine and to a lesser extent by the addition of aspartic and glutamic acids and glycine. A deficiency of cystine or glutamine results in cellular degeneration within 3 to 5 days, whereas the cells remain in good condition for 2 to 3 weeks in the absence of each of the remaining 12 essential amino acids. The results obtained with RM3-56 are compared with strains HeLa, L, and U12, whose amino acid requirements have been investigated under similar conditions.