The histochemical demonstration of protein-bound sulfhydryl groups and disulfide bonds in human hair by a new staining method (DACM staining).

A new fluorogenic maleimide DACM, i.e., N(7-dimethyl amino-4-methyl coumarinyl) maleimide, does not fluoresce by itself. It is specifically combined with --SH groups and becomes fluorescent (lambda ex: 400 nm, lambda em: 485 nm). At this range of excitation the frozen skin section has no native fluorescence because the emission maximum of DACM does not overlap with any of aromatic residues of proteins such as tryptophane. S--S groups can be demonstrated with DACM by inhibiting native --SH and then reducing SS to --SH. --Sh was generally abundant at the bulb region. --SH of hair cortex was more concentrated at keratogenous zone. Further up in the follicle, --SH of hair cortex was gradually decreased, although at the region of isthmus, --SH reaction of the hair cortex was still moderately strong. Outer root sheath had --SH from the upper bulb to the surface of the epidermis. One the other hand, no S--S was demonstrable at the bulb region. At the level of keratogenous zone, however, S--S linkages of hair cortex and inner root sheath began to appear and further up in the follicle S--S linkages were increased gradually. Outer root sheath had no S--S linkages by DACM staining up until it is keratinized along the hair canal in the upper follicle. The concentration of --SH and S--S thus seemed to be reciprocal; --SH is found in non-keratinized tissues, whereas S--S is abundant in keratinized areas. These findings are at some variance with conventional data, which suggest, for example, that --SH groups disappear suddenly above the keratogenous zone.