The γA2-subgroup of γA-globulins, previously delineated by antigenic studies, was found to differ strikingly from other immunoglobulins in the manner in which the polypeptide chains are bound together. The heavy and light chains were not linked to each other by disulfide bonds. Instead the light chains were disulfide linked to one another, and were present in the γA2-molecule as disulfide bridged L-L dimers.
Antisera specific for γA2-proteins indicated the occurrence of two different antigenic types in all normal sera as well as saliva and colostrum. Both of these showed the unique interchain disulfide linkage. Quantitative analyses indicated higher levels of γA2-proteins in external secretions.