Stoichiometry of the aldehyde fuchsin staining reaction for proteins

Model systems of agar films containing known concentrations of bovine serum albumin and alpha-chymotrypsinogen were stained with aldehyde fuchsin after oxidation with acidified permanganate solution. These films were scanned in a scanning microphotometer to determine the mean extinction and the total extinction of predetermined areas. Results indicate that the dye binds quantitatively to the proteins. Blocking the acidic side groups of the proteins inhibited the binding of the dye. The degree of inhibition was directly related to the number of sulfhydryl or carboxyl groups that were blocked. Similar blocking reactions performed on the type "A" neurosecretory cells of the pars intercerebralis of the insect Oncopeltus fasciatus gave similar results. Analysis of the dye protein complexes gave a dye to acidic group ratio of 1:1.