Normal counterparts to Bence-Jones proteins: free L polypeptide chains of human gamma-globulin.

Bence-Jones proteins are commonly found in patients with multiple myeloma and have been defined classically' as abnormal urinary proteins that have characteristic thermosolubility properties. Structural studies2 have shown that BenceJones proteins are similar or identical to the light (L) polypeptide chains isolated from the myeloma globulin of the same patient. Taken in conjunction with the results of studies of their biosynthesis,3'4 this finding suggests that BenceJones proteins are free L chains that have not been incorporated into the myeloma proteins. Because of their structural similarities to chains of myeloma proteins, it was predicted' that chains of normal y-globulins would also have the properties of Bence-Jones proteins. Subsequently, L chains of 7S 7y-globulin from normal individuals were found to resemble Bence-Jones proteins in both physicochemical2 and antigenic6 characteristics. Recently, y.-globulins of low molecular weight (,yL-globulins) have been isolated from the plasma7 and urine'-" of normal human subjects. These proteins were shown12 to have close antigenic relationships to the S fragment, a split product of human 7S y-globulin that is known to contain L chains.6 It has also been found'2"3 that the 'yL-globulins contain antigenic counterparts to the two main antigenic types'41" Of Bence-Jones proteins. All of the above findings suggested that the YL-globulins are similar to the L chains obtained from dissociated normal 7S y-globulins and prompted the present comparative study. The results indicate that normal 7L components and L chains are alike in antigenic structure, thermosolubility, conformational stability, and molecular weight. They appear to be normal counterparts to Bence-Jones proteins. Materials and Methods.-Jsolation of 'YL-globulins-Plasma 'YL-globulin: 2140 ml of pooled normal plasma was subjected to two successive ultrafiltrations, as described previously.7 The concentrated ultrafiltrate, containing the 'yL-globulin, had a volume of 3.6 ml and a protein content of 73 mg as determined by a modified Folin procedure's with human albumin as standard. It was used for some of the immunochemical experiments. 'yL-globulin was purified further from a 2.2 ml aliquot of the concentrated ultrafiltrate by zone electrophoresis at pH 8.6 on a Pevikon block. 17 As a reference, normal plasma was separated on an adjacent part of the same block. The separated ultrafiltrate contained a post e-globulin fraction and proteins corresponding to all of the main electrophoretic fractions of plasma. Material corresponding to the slow moving part of the reference plasma 'v-globulin zone was concentrated to 1.2 ml by ultrafiltration, using Visking 2 7 2 in. tubing.'8 The concentrated fraction contained 1.7 mg protein'8 representing 6-7% of the total protein recovered from the block. It contained 'YL-globulin, but was free from 7S 'a-globulin as shown by Ouchterlony plate analyses, using antisera to a-globulin and human serum. The preparation also contained a protein that was immunologically unrelated to 'y-globulin. Urinary -YL-globulin: The urinary 'YL-globulin fraction used in the immunochemical experiments was obtained by submitting pooled urine from normal male subjects to two successive ultrafiltrationS 7, 11 The 'vL-globulin preparations used in the other experiments were purified as follows: 10.0 1. of pooled normal urine was concentrated by ultrafiltration, using Visking 2 7% 2 in. tubing of comparatively low permeability.'8 6.9 ml of the urine concentrate, corresponding to 8.2 1. of urine,