The histochemical distribution of protein bound sulfhydryl groups in human epidermis by the new staining method.

Recently, we synthesized a new fluorescent thiol reagent, N-(7-dimethylamino-4-methylcoumarinyl)-maleimide (DACM) which is nonfluorescent by itself but will react readily with -SH groups to form highly fluorescent addition products. By the use of this reagent, we studied the localization and concentration of -SH groups and S--S linkages in the human epidermis. The distribution of -SH groups in living layers was abundant in cytoplasm but not in nuclei. The fluorescence was concentrated on the cell membrane or intercellular spaces (MIC parts) and was increased at the spino-granular junction. In the horny layer, the fluorescence of the MIC parts appeared brilliantly in the lower layers and decreased gradually. On the other hand, the fluorescence of cytoplasm in keratinized cells in the stratum corneum was faint. The localization of S--S linkages was not a characteristic of the living layers, but appeared abruptly at the junction of living and horny layers. The fluorescence was localized to the MIC parts and disappeared gradually. The distribution of S--S linkages appeared to be very low in the cytoplasm of keratinized cells. No substantial fluorescence was localized on keratohyalin granules even after reduction.