Protein synthesis in stimulated lymphocytes: II. Amino acid requirements

Abstract

The amino acids required for protein synthesis by phytohemagglutinin (PHA) and antigen stimulated lymphocytes have been determined by measuring the kinetics of protein synthesis in amino acid deficient media. Stimulated lymphocytes have a partial requirement for serine in addition to the 13 amino acids which Eagle (1) found to be essential for mammalian cell cultures. Asparagine is not required for the lymphocyte response. This observation supports the suggestion that l-asparaginase inhibits lymphocyte blastogenesis by its action on the membrane rather than by depletion of exogenous asparagine. With the exception of serine, tryptophan, and isoleucine, the omission of an essential amino acid results in complete inhibition of PHA induced protein synthesis. In the absence of either tryptophan or isoleucine, the rate of protein synthesis is unaffected during the first 30 hr of incubation but subsequently declines rapidly to that of unstimulated cultures, suggesting a possible role for tryptophan and isoleucine in the regulation of the lymphocyte cell cycle. The inhibition of protein synthesis by amino acid deficiencies is reversible upon replacement of the missing amino acid.