Complexes of albumin and alpha 1-antitrypsin with Fc-fragment of IgA monomer are disulfide-bound to penultimate C-terminal cysteine in the C alpha 3-domain
Vaerman, J.P.; Hagiwara, K.; Kobayashi, K.; Rits, M.
Immunology Letters 15(1): 67-72
Six IgA myeloma sera, containing albumin (ALB)-IgA and alpha 1-antitrypsin (alpha 1-AT)-IgA complexes (CXs), were gel-filtered on Ultrogel AcA22. The CXs were eluted between monomeric and dimeric IgA. The CX-containing fractions were digested with three IgA-proteases: ALB and alpha 1-AT remained bound to Fc alpha-, but not to Fab alpha-fragments. Short (less than 2 h) peptic digestion entirely released free ALB and alpha 1-AT from the CXs, indicating that these proteins are linked to the third constant domain of the alpha-chain. Identical results were obtained with anti-ALB immunosorbent-purified ALB-IgA CXs. Reduction-alkylation of ALB or alpha 1-AT bound to IgA or Fc alpha confirmed disulfide binding. The data support the binding of ALB and alpha 1-AT to the same penultimate C-terminal cysteine of the alpha-chain as that which binds the J-chain.