Superoxide Dismutase in Epidermis (1)

Abstract

Superoxide dismutase (SOD), which catalytically scavenges superoxide anion (O–2), constitutes an essential defense against the toxicity of oxygen. We investigated the enzyme activity of pig skin epidermis. SOD activity was determined by monitoring the inhibitory effect of SOD on red formazan formation from neotetrazolium, which depends on (O–2) generation. (O–2) was generated by the hypoxanthine‐xanthine oxidase reaction. Pig epidermis contained significant amounts of heat‐labile SOD activity which was proportional to the added epidermal homogenate. The optimal pH of the reaction was between pH 8.2 and 8.5. Metallochelating agents such as cyanide, sodium azide, and diethyldithiocarbamate (DDC) inhibited the epidermal SOD activity in a dose‐dependent manner. It has been known that two types of SOD, a Cu, Zn‐type and a Mn‐type, are present in eukaryotes; that the latter is insensitive to cyanide inhibition. Using this property, the main SOD present in the epidermis was hypothesized to be the Cu, Zn‐type (8.6 ±1.1 unit/mg protein; around 75%); the Mn‐type was a minor component (2.8 ± 0.2 unit/mg protein; around 25%). SOD staining following acrylamide disc gel electrophoresis revealed two epidermal SOD bands, one of which was abolished by the addition of cyanide. These results are consistent with the view that pig epidermis contains two types of SOD, a Cu, Zn‐type and a Mn‐type; the former appears to be predominant.

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