The low-molecular-weight SH-protease inhibitor in rat skin is epidermal.

The epidermis and dermis of rat skin were separated and the presence of the high-molecular-weight SH-protease inhibitor I1 and the low-molecular-weight inhibitor I2 in both was studied. Gel filtrations of the extracts revealed that 97% of the epidermal inhibitor activity was due to I2 and 89% of the dermal activity to I1. The presence of I2 mainly in the epidermis extract was confirmed by immunodiffusion of specific rabbit anti-I2 serum against purified I2, epidermis and dermis extracts, and rat serum. Most of the immunoreactive protein was seen in the epidermis extract, traces in the dermis extract and none in the rat serum. I2 was localized in rat skin by indirect immunofluorescence using rabbit anti-I2 serum and fluorescein isothiocyanate conjugate of goat anti-rabbit immunoglobulins. Intense fluorescence, much brighter than in the controls treated with rabbit non-immune serum, was seen in the epidermis, being most pronounced in the cytoplasms of cells in the granular layer. The weak fluorescence of the hair follicles, sebaceous glands, connective tissue cells and fibres was unspecific and was also seen in the controls. In view of its epidermal location, the name epidermal SH-protease inhibitor is suggested for I2.