Catalase protein and enzymatic activity in ascorbic acid resistant and susceptible cells. (A) Immunoblots and densitometric analyses of catalase protein, and (B) enzymatic activity in ascorbic acid resistant cancer cell lines (BT-20, 23132/87, SKOV-3) and ascorbic acid susceptible cancer cell lines (U-251, U-87). The protein level of catalase in ascorbic acid resistant BT-20 cells is significantly different (p < 0.001) to the levels in 23132/87, SKOV-3 and the ascorbic acid susceptible cell lines U-251, U-87. There is a correlation between catalase activity and resistance to the ascorbic acid mediated cytotoxic effect. The results shown are representative for 3 independent analyses. Values are expressed as mean ± standard deviation and significant differences (p ≤ 0.01) are shown (**) compared to U-251 and U-87, respectively.