Demonstration of protein-bound sulfhydryl and disulfide groups with fluorescent mercurials

Four mercurials, mercury orange, 4-(p-dimethylamino benzene azo) phenyl mercuric acetate, fluorescein mercuric acetate, and mercurochrome were tested and found to be successful reagents for demonstrating protein-bound SH and SS groups. Of this group, 4-(p-dimethylamino benzene azo) phenyl mercuric acetate gave the weakest fluorescence and mercurochrome gave the most useful contrast by direct microscopy. While no quantitative data are yet available, qualitatively reliable patterns were obtained after one hour in the staining solutions.