Interactions between Immunoglobulin Polypeptide Chains*

1. The dimerization of reduced and alkylated Bence Jones proteins was studied by gel chromatography and circular dichroic (CD) measurements. The association con-stants of two type X proteins, as estimated by gel chromatography, were 105 and 2xlO6M~1 at pH 5.5, 25°C. The changes in the CD spectrum in the aromatic absorp-tion region with protein concentration and those with pH on the alkaline side indicate that the monomeric and dimeric forms of type X proteins are different from each other as regards the environment of tyrosyl residues. 2. The conformation of IgG molecules reconstituted from the alkylated H chain of a myeloma protein and various specimens of alkylated Bence Jones proteins was studied by CD measurements. The CD spectra of the recombinants were different depending on the specimens of L chains used, even if the antigenic type was the same. This indicates that the conformational change observed when H and L chains recombine is mainly associated with the conformational change of the variable portion of the L chain.