Metabolism of Bence Jones Proteins*

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Abstract
The metabolic fate of Bence Jones proteins was investigated in fifteen studies in ten patients. Three different Bence Jones proteins were labeled with I131, and the amount and rate of Bence Jones protein lost in the urine and catabolized in the body were determined. Both catabolism and urinary loss contributed to the removal of Bence Jones protein from the blood. The relative contributions of catabolism and of urinary loss depended on the quantity of Bence Jones protein formed and on the renal status of the subject. The proteinuric rate ranged from 0 to 3.0% of the intravascular pool per hour. The proteinuric rate was highest in patients synthesizing Bence Jones protein. The possibility that Bence Jones proteins or similar gamma-microglobulins are filtered by the glomerulus and reabsorbed by normal renal tubular cells is considered. Labeled Bence Jones protein was catabolized at rates of 1.8 to 42% of the intravascular pool per hour. The catabolic rate correlated with renal functional capacity. In subjects with normal renal function, daily catabolic rates of 10 to 42% per hour were observed. Lower catabolic rates (1.8 to 3.9% per hour) were observed in patients with poor renal function. These observations indicate that the kidneys may play a role in the catabolism of Bence Jones proteins. The demonstration that catabolism contributes significantly to the metabolic fate of Bence Jones protein indicates that the urinary Bence Jones protein is only a portion of the total Bence Jones protein synthesized per day. Factors determining the urinary losses of Bence Jones protein are discussed.