Incorporation of N15-L-aspartic acid into the abnormal serum and urine proteins of multiple myeloma; studies of the inter-relationship of these proteins.

In a consideration of the abnormalities of protein metabolism observed in multiple myeloma, a number of fundamental problems remain unsolved. To state just two of these, it remains to be determined (a) precisely what relationship the abnormal serum globulins of myeloma bear to normal serum gamma globulin, and (b) what is the nature of the possible inter-relationship between the abnormal serum protein and urinary (BenceJones) proteins of myeloma when both are present in a particular case. The electrophoretic homogeneity of these abnormal serum and urinary proteins constitutes one of their major physicochemical features. Using this criterion of electrophoretic homogeneity to identify these abnormal proteins, it has been found (1-3) that approximately one-half of a group of one hundred myeloma patients has both a serum and a urine protein abnormality; another one-third of these cases shows only a serum abnormality, with no characteristic proteinuria, and the remaining one-sixth of the cases exhibits a discrete urine protein peak with no abnormal protein peak demonstrable in the serum. The present study was designed to elucidate the inter-relationship between the serum and urine proteins in the first group of cases, i.e., in those patients with both a serum and a urine abnormality. For this purpose, an isotopically-labelled amino acid was administered to a patient with multiple myeloma and the incorporation and turnover of this label was followed in these two proteins (Ms hereinafter designates the abnormal serum globulin, and Mu the urinary [Bence-Jones] protein). If the time-characteristics of the isotope