Plasma 3 S γ1 -Globulin: Identity with Erythrocyte Carbonic Anhydrase B

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Abstract
The 3 S γ1 , 2 S γ2 , and 0.5 S γ2 fractions of human plasma are heterogeneous in protein composition. Although each fraction contained a relatively small amount of protein antigenically related to the immunoglobulin light chains, most of the proteins were unrelated to immunogloublin G or its light chains. Of the 3 S γ1 -globulins the greater part was immunochemically identical to carbonic anhydrase B and had carbonic anhydrase activity. These findings explain earlier reports of an immunochemical similarity between 3 S γ1 -globulins and immunoglobulin light chains in spite of marked differences in amino acid and peptide composition between the two. Apparently not all plasma γ-globulins are necessarily immunoglobulins.