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The Utilization and Formation of Dicarboxylic Amino Acids by Cell Suspensions of Normal and Malignant Lymphatic Tissues^*

( Division of Protein Chemistry, M. D. Anderson Hospital for Cancer Research, University of Texas, Houston, Texas)

Cell suspensions of rabbit appendix, rat thymus, mouse spleen, and two mouse lymphosarcomas were incubated with acetate-2-C¹⁴, DL-glutamate-2-C¹⁴, succinate-2-C¹⁴, or DL-aspartate-4-C¹⁴. Respiration, oxidation of labeled carbon to CO₂, and incorporation into cell protein were measured. A method was devised to separate free aspartate and glutamate from radioactive contaminants, and the specific activities of these amino acids were determined.

The Mecca lymphosarcoma utilized exogenous acetate less effectively than the other tissues; however, in the presence of glucose, both tumors utilized exogenous succinate more completely than did the normal tissues. Exogenous aspartate was not oxidized or incorporated into protein more rapidly by the tumors than by the normal tissues.

Labeled aspartate and glutamate were formed from each of the substrates, and the Gardner tumor formed proline and glycine from acetate. The ratio of the specific activity of glutamate to aspartate depended on the substrate used and the experimental conditions. After incubation with succinate, the specific activity of aspartate was 2–5 times that of glutamate. Addition of glucose to the medium increased the labeling of glutamate so that it was nearly equal to that of aspartate. When acetate-2-C¹⁴ or acetate* plus succinate were the precursors, glutamate and aspartate were also about equally labeled; however, in the presence of acetate* plus glucose, the free glutamate of the Gardner tumor was considerably more radioactive than aspartate. The possibility was suggested that the low endogenous concentration of free aspartate previously observed in the lymphosarcomas was in part attributable to the high rate of glycolysis of neoplasms.

^* Aided in part by grants from the National Cancer Institute, National Institutes of Health, U.S. Public Health Service (C-1831), and the American Cancer Society.

Received 2/ 8/54.