Effect of glutamine analogs on amino acid incorporation into protein of some normal and neoplastic cells in vitro.

Glutamine is a marked stimulant for protein synthesis by various isolated cellular systems. Thus, Eagle, Piez, and Fleishman ($) report that the incorporation of phenylalanine into protein of nongrowing human tissue cultures is stimulated twofold by glutamine. Similarly, Rychlik and Sorm (15) found that glutamine brings about a several-fold increase in the formation of amylase and proteases by mouse pancreas slices. We had earlier reported (10) that glutamine stimulates the incorporation of several amino acids into Ehrlich ascites tumor cells in vitro, and in the absence of this essential amino acid its analog, methionine sulfoximine, inhibits the incorporation of these other amino acids. This inhibition by methionine sulfoximine was shown to be due to a block in glutamine synthesis and was prevented by low concentrations of glutamine. The results indicated tha t the rate of protein formation by the washed tumor cells was determined by the synthesis of glutamine in these cells. This important role of glutamine led us to investigate the effect of methionine sulfoximine and other glutamine analogs on the incorporation of radioactive amino acids into protein of several other tissues. The incorporation of valine-C 14 and isoleucine-C 14 was used to determine the over-all effect of the analogs on protein synthesis, while the incorporation of glutamine-C ~4 was used to determine the direct effect of the analogs. 1