ULTRAVIOLET-A-DEPENDENT INHIBITION OF CYTOPLASMIC ACONITASE ACTIVITY OF IRON REGULATORY PROTEIN-1 IN NCTC-2544 KERATINOCYTES

The aconitase activity of the cytoplasmic iron regulatory protein-1 of NCTC 2544 keratinocytes is effectively inhibited by physiological dos es of UVA, The time course of the photoinactivation is biphasic, A fas t step is first observed corresponding to about 50% inactivation after exposure to 5 J/cm(2) of WA followed by a much slower photoinactivati on at higher doses. The water-soluble antioxidant N-acetylcysteine onl y partially inhibits the photoinduced inactivation of the cytoplasmic aconitase function, whereas the lipophilic vitamin E, the iron chelato r, desferrioxamine and the superoxide dismutase inhibitor, diethyldith iocarbamate do not protect at all. As a consequence, reactive oxygen s pecies such as O-2(.-), H2O2 and lipid peroxides and hydroperoxides se em to play a rather minor role in the inactivation induced by the WA p hotooxidative stress although an oxidative stress produced by O-2(.-) and H2O2 is known to inhibit reversibly and effectively cytoplasmic ac onitase activity in mammalian cells.