Schauenstein E, Sorger S, Reiter M, Dachs F
J Immunol Methods. 1982;50(1):51-6. doi: 10.1016/0022-1759(82)90303-9.
The IgG fraction was isolated from freshly taken blood serum of health persons (male and female) by column chromatography on QAE-Sephadex. After 30 min incubation with DTNB (5,5'-dithio-(2,2'-dinitro)-benzoate) the average photometrically determined quantity of thio-anions was 0.24 +/- 0.02 SH/mole IgG. Since this result remained unchanged even after 24 h incubation with DTNB, interaction with masked thiol groups cannot be assumed. If, however, the serum was incubated with DTNB for 24 h and the IgG fraction then isolated and treated with thioglycolate, an average of 1.51 +/- 0.39 moles of thio-anions were liberated per mole of IgG. This indicates that on 24 h interaction with IgG, DTNB not only reacts with free SH groups, but also opens S-S bonds by a disulfide exchange reaction. The amount of thio-anions resulting from such opened disulfide bonds was calculated as the difference between 1.51 0.24, i.e., 0.64 S-S/mole IgG. This would be accounted for if approximately 54% of the IgG fraction is composed of a subfraction containing 1 labile disulfide bone per mole. The average of 1.51 thio-anions per mole IgG resulted from 130 single values with an essentially normal statistical distribution and standard deviation well within the usual biological range.
