Figure 6

p-BSQ mimics AECS causing oxidative modification and proteolysis in vitro: prevention by vitamin C. A, Dose-dependent AECS/p-BSQ/p-BQ-induced protein carbonyl formation in BSA in the presence or absence of vitamin C, as measured spectrophotometrically. The incubation mixture was same as in Fig.5A using AECS (50 μl), p-BSQ (90 nmoles) or p-BQ (45 nmoles). Small bars over the points in the graph represent mean ± SD. B, Conversion of p-BSQ to p-BQ by disproportionation reaction or by SOD/cytochrome c catalysed oxidation. p-BSQ (180 nmols) was incubated in 200 μl of 50 mM phosphate buffer, pH 7.4 at 37°C in air with or without the presence of Cu, Zn-SOD (30 μg) and cytochromec (180 nmoles), incubation was carried out in air. Aliquots were taken, diluted with mobile solvent and p-BQ estimated by HPLC. Details are given in Methods. ↓ Indicates addition of vitamin C (200 μM). C, Degradation of guinea pig lung microsomal proteins as a function of p-BSQ concentration. D, E, Degradation of guinea pig lung microsomal proteins by p-BSQ (180 nmoles) and p-BQ (90 nmoles) in the presence and absence of vitamin C (200 μM). Conditions are same as described previously [7]. Similar observations were made in three independent experiments.