Pressure variation of enzymatic reaction rates: IV. Xanthine oxidase and superoxide dismutase.

Effect of pressure on activities of O-(2)-producing enzyme xanthine oxidase (XO) and O-(2)-scavenging enzyme superoxide dismutase (SOD) has been investigated to 1000 bar. Methods used included spectrophotometric determinations of inhibition by SOD of O-(2)-induced reduction of cytochrome c and oxidation of ascorbic acids. It was found that (1) pressure increases XO activity, the activation volume being delta V not equal to = -45 +/- 5 cm3/mol; and (2) pressure decreases SOD activity, the activation volume being delta V not equal to = 30 +/- 5 cm3/mol. Under the conditions of these experiments, pressure therefore favors an increase in O-(2) activity. This may lead to increased cell damage in organisms in high-pressure situations even if oxygen concentration is held constant.