The effect of various metal ions and chelating agents on the formation of noncovalently and covalently linked IgM polymers.

The influence of various concentrations of Mg2+, Ca2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, EDTA, or 8-hydroxyquinoline-5-sulfonic acid on the formation in vitro of polymeric IgM from reduced and dissociated IgM has been investigated. 4-200muM Zn, Cd, or Hg ions in the dialysis buffer used for reassociation resulted in the formation of a homogeneous polymer peak sedimenting as 19S IgM, whereas the other metal ions resulted in the formation of polymers sedimenting mostly as tetramers, pentamers (19S IgM), and hexamers. Dialysis in the presence of 1 and 3mM EDTA or 8-hydroxyquinoline-5-sulfonic acid gave slight polymer formation; 10 mM of the agents gave none. Ca, Mg, Fe, Ni, Zn, Cd, or Hg ions regularly gave only noncovalently linked polymers, whereas Cu ions in particular, but also Co and, to a minor extent, Mn ions catalyzed the formation of covalently linked polymers. Experiments performed with Mg, Ca, Ni, and Zn ions or with Cu and Zn ions in the same buffer during reassociation showed that Zn ions inhibit the effect of the other ions on polymer assembly and covalent stabilization.