= IgG chain reduction experiment
{c}
<Gerald M. Edelman> reduced <IgG> <disulfide bonds> and used dissociating <chemical solutions>, including $6\,\mathrm{mol\,L^{-1}}$ <urea>. Ultracentrifugal analysis showed a decrease in <molar mass>, supporting a multichain <protein>. In the comparison reproduced in his lecture, <starch gel electrophoresis> in <urea> separated serum <IgG> and a urinary <protein> from the same patient, alongside their reduced and <alkylation>-treated preparations. The untreated samples provided the treatment comparison; the urinary material provided a chain-identity comparison. The treated serum sample revealed heavy- and light-chain bands. Two-dimensional <peptide mapping> compared the urinary <protein> with the isolated <immunoglobulin light chain>. Together these readouts supported a shared chain identity.<Antibody Structure and Molecular Immunology by Gerald M. Edelman>[Gerald M. Edelman, Antibody Structure and Molecular Immunology, Nobel Lecture dated 12 December 1972, printed pp. 33–34 and Figure 2a–b: dissociation, four comparison lanes and peptide maps]{ref}
The controls address distinct alternatives. Treatment-dependent separation supports chains joined in the starting <protein>; a matching <gel electrophoresis> position alone would not uniquely identify a chain. Agreement of <peptide mapping> adds an independent chemical comparison. Neither readout gives atomic coordinates, and this patient's preparation does not establish a common <protein primary structure> for all <antibodies>.
<Reduction> targets <protein disulfide bonds>, while <protein denaturation> weakens the folded assembly. Neither operation is the <proteolysis> that cuts <peptide bonds>. This explains why chain separation and <Papain digestion of IgG> give different inventories: four intact chain backbones in the first case, three assembled fragments in the second.
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