Coulometric titration of proteins with silver(I)

The sulfhydryl groups of some proteins were studied by a coulometric argentometric titration; disulfide groups in the presence of sulfite were titrated by the same technique. Direct procedures and a technique utilizing excess coulometrically generated silver(I) were used. The latter method enabled small samples (20-1000 μg of protein) to be titrated with a precision of less than 4%. The proteins were generally titrated in both the native state and the denatured state (8 M urea). Bovine serum albumin, α-chymotrypsin, glutathione reductase, human hemoglobin, insulin, β-lactoglobulin, and ovalbumin were examined and the results compared to those of previous workers.