The inability of sarcoma RD3 to utilize D-histidine for protein synthesis.

The search for a distinguishing biochemical property of tumor tissue as compared with normal mammalian tissue led Kögl and Erxleben (7) to investigate the nature of the amino acids which make up various tumor tissue proteins. Their find ings indicated that, although most of the protein of tumors was composed of L-amino acids (the "naturally" occurring form), some tumors con tained substantial amounts of the D-form of cer tain amino acids and that a common feature ap peared to be the presence of D-glutamic acid. They were unable to isolate any appreciable amount of D-glutamic acid from the protein of normal tissues. The presence of appreciable amounts of D-amino acid in tumors has not, however, been confirmed, and the controversy has been the subject of two excellent reviews (9, 11). In view of the fact that the mammalian diet does not normally contain appreciable amounts of D-amino acids and that D-amino acids are not de tectable in the body as a result of metabolism, it seems unlikely that D-amino acids would occur in the normal or neoplastic tissues of mammals. How ever, the possibility remains that, if a D-amino acid is administered to a tumor-bearing animal, the tumor might accept the D-amino acid and in corporate it into its proteins, while the normal tissues may not do so. The results of Wiseman (12) show that the rat small intestine in vitro is incapable of actively concentrating D-histidine, while, on the other hand, Ehrlich mouse ascites carcinoma cells can do so (1). The experiments described below, however, show that the injected D-histidine was not incorporated into the protein of the rat RD3 sarcoma, liver, or muscle.