The Use of Labeled Amino Acids in the Study of the Protein Metabolism of Normal and Malignant Tissues: A Review^*

A reactivation of interest in studies on the mechanism of protein synthesis has come about as a result of the availability of C¹⁴-labeled amino acids. Although much information has been gathered, the crucial decisions as to whether phosphate bond energy is directly concerned in synthesis of the peptide chain, and whether the proteolytic enzymes participate, are still lacking. In application of the isotope technics to the cancer problem, no specific reaction has as yet been uncovered in which malignant tissue as a class differs qualitatively or quantitatively from all normal tissues. The dynamic aspects of the protein metabolism of tumors have thus far been the subject of only fragmentary studies. There appears to be a good opportunity for exploration with isotope technics of the property of tumors to continue to build new protein under dietary circumstances in which the remainder of the animal loses weight.