Inhibition of the growth of mammalian cells in culture by amino acids and the isolation and characterization ofL-phenylalanine-resistant mutants modifyingL-phenylalanine transport

Abstract

Raising the concentration of phenylalanine and other amino acids in MEM leads to the inhibition of growth and in some cases to death of A9, Balb 3T3, SV40 Balb 3T3 (SVT2), CHO, and WI38. All cells tested exhibited some similar sensitivities to certain of the amino acids, but there were some unique differences. Phenylalanine-resistant mutants (Phe r )of A9 were isolated that had modified phenylalanine-transport properties. These mutants can be isolated by a single-step selection procedure. A Lineweaver-Burk plot of initial rates of phenylalanine uptake by A9 and mutants showed a biphasic curve suggesting two transport systems. The Phe r mutants had altered properties of both systems. It is suggested that the selection of clones resistant to high concentrations of several of the natural amino acid may be used as a general method for the isolation of mutants affecting the various amino acid transport systems in mammalian cells.