Induced formation of leucine decarboxylase in Proteus vulgaris.

1. The serum myeloma protein and urinary Bence-Jones protein of mice carrying the MPC-2 plasma-cell neoplasm have been purified by chromatography on ion-exchange diethylaminoethylcellulose and characterized. 2. The neoplastic plasma cells were found to form both proteins. Biosynthesis was studied by incubating sliced tumour tissue in vitro and following the incorporation of [14C]amino acids into the Bence-Jones protein and myeloma protein isolated by chromatography on diethylaminoethylcellulose and by precipitation with rabbit antisera. The time course of incorporation of radioactive amino acid into the two proteins is consistent with the view that Bence-Jones and myeloma proteins were formed independently by the neoplastic plasma cells and that neither protein was a precursor or breakdown product ofthe other. Approximately two molecules of Bence-Jones protein were formed for each molecule of myeloma protein. 3. The pool of extracellular plus intracellular protein associated with MPC-2 tumour tissue was determined by isotope-dilution techniques employing M3I-labelled Bence-Jones and 131I-labelled myeloma protein. About 3'6 mg. of myeloma protein and 0*4 mg. of Bence-Jones protein were found in 1 g. of tumour tissue (wet weight). This difference is probably caused by the rapid clearance of Bence-Jones protein from the plasma and extracellular fluid by excretion through the urinary tract.