Albumin isoforms - (Oct/03/2016 )

protein a should bind the igg by the tail, leaving the antigen binding sites (fab) free. if there is no tail (fc) then the fragment shouldn't bind to protein a.

if you release the bound antigen from the protein a with sds-page sample buffer, then you should also obtain the igg light chains (the remainder of the molecule is crosslinked to the protein a). it will also prevent you from reusing the bound igg. i wouldn't recommend this.

the urea/thiourea and dtt may also strip the light chains from the igg, thereby rendering the beads ineffective.

my recommendation would be to solubilize the pellet in a non-denaturing medium, bind to the protein a beads, release by reducing (or raising, if necessary) the pH, then introducing the 2d lysis buffer to the released protein. assuming no proteases to fragment the protein a or igg, you should not see any igg fragments in the gels (also assuming that there is no igg in the synovial fluid which may bind to any free protein a on the beads).

Thank you mdfenko. Invaluable advice as always.