Ultrastructural localization of superoxide dismutase in human skin

The ultrastructural localization of copper and zinc superoxide dismutase (Cu,Zn-SOD) and manganese superoxide dismutase (Mn-SOD) was investigated in normal human skin by the post-embedding immunogold staining method. Epidermal keratinocytes were positive for both Cu,Zn-SOD and Mn-SOD. The Cu,Zn-SOD was predominantly located in the cytoplasm with a slight labelling on the mitochondria. The basal cells were remarkably positive for Cu,Zn-SOD and the upper spinous or granular cells faintly positive for this enzyme. In contrast to Cu,Zn-SOD labelling, Mn-SOD labelling was mostly restricted to the mitochondria. A similar labelling pattern was observed in dermal fibroblasts, endothelial cells, melanocytes, and in various epidermal appendageal cells (i.e. outer root sheath cells, sweat ducts and eccrine sweat gland cells). Thus the subcellular localization of Cu,Zn-SOD and Mn-SOD in the skin was similar among various cell types. Although no evidence for the peroxisomal localization of Cu,Zn-SOD was obtained in the present study, this could be due to a marked fragility of peroxisome that has not been identified in epidermal keratinocytes.