Metabolism of Bence Jones Proteins.

Bence Jones proteins are molecules of about 40,000 mol wt present in the urine of many patients with plasma cell malignancy. These microglobulins, which are synthesized in plasma-cell tumors (1, 2), share many immunochemical and physicochemical features with the larger 6.6 S y-globulins. That Bence Jones proteins are similar to or identical with components of the larger y-globulins has been suggested (3-5). Evidence has been recently obtained that microglobulin components similar to Bence Jones proteins may be present in normal urine (6-8) and serum (9). The rate of synthesis and metabolic fate of these proteins are poorly understood, both in malignant plasma cell diseases and in the normal state. Putnam and Hardy (10) and Osserman and associates ( 11 ) observed that newly synthesized Bence Jones protein was excreted rapidly by patients with multiple myeloma; they suggested that massive proteinuria (as high as 50 g per day) may be present and that Bence Jones proteins are excretory products of protein metabolism. It was not clear in these studies whether all the newly synthesized Bence Jones protein was excreted or whether only a part was excreted and the remainder catabolized. Evidence that some Bence Jones protein is catabolized was noted by Meyer and Putnam (12), who reported that only a fraction of injected C14-labeled Bence Jones protein appeared in the urine of a single patient with multiple myeloma when he was reinjected with his own labeled Bence Jones protein. Rabbits given the same protein also excreted only a part of the injected protein intact. Perkins, Doherty, and Towbin (13) reported after two studies with intravenously administered I131-labeled Bence Jones protein that only 20% of the injected 1131 was excreted bound to protein, the remaining 80%o being excreted as iodide, presumably representing