The rates of immunoglobulin synthesis have been examined in two MFC-11 cell lines which were independently adapted to tissue culture and in light-chain-producing variants derived from each of them. One cell line synthesized 2.5 pg immunoglobulin/cell/h, while the other synthesized 3.6 pg immunoglobulin/cell/h. The ratio of heavy and light chains in the two cell lines was approximately the same, and the size of the intracellular pool of immunoglobulin was proportioned to the rate of synthesis. Variants which had spontaneously lost the ability to produce heavy chains continued to synthesize light chains at approximately the same rate as their parent cell line.

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