The free amino acid pool in L-strain fibroblasts

Abstract

L-strain mouse fibroblasts were grown in stationary bottle cultures in a serum-free medium and harvested during the logarithmic growth phase. A qualitative analysis of the intracellular water showed that all the amino acids in the growth medium were present in the free amino acid pool. However, quantitatively it was different from the medium. Grossly, the free intracellular amino acids could be separated into three major groups on the basis of their capacity to be pooled from this medium. Glycine, alanine, aspartic acid, threonine, proline and glutamic acid constitute the first group and are distinguished by their capacity to be concentrated in cell water. Group II amino acids, although present in significant amounts in cell water, are not concentrated. Leucine, isoleucine, valine, methionine, phenylalanine and tyrosine make up this group. Arginine, histidine and lysine comprise group III and can only be found in traces. Quantitative studies indicated that L cells retain cell proteins, nucleic acids and free amino acids to a large extent after three rapid washes with a balanced salt solution. The reduced level of any free amino acid occurs uniformly with losses in protein, nucleic acids or other amino acids; this suggests that these cells are not leaking or utilizing free amino acids to any degree during the washing procedure. The reductions apparently reflect losses of whole cells through handling or breakage.