Table 3. NADH-mediated superoxide production by HoxFU in the presence of O2 a.
| Superoxide production | ||
| Specific activity | Turnover rate | |
| O2 concentration in the assay [µM] | [nmol/min/mg] | [min−1] |
| 300 µM (air-saturated) | 53.5±7.4 | 5.9±0.8 |
| 1428 µM (100% O2) | 465.0±23.9 | 51.2±2.6 |
| 1428 µM (100% O2)+650 Units SODb | 13.0±4.9 | 1.4±0.5 |
a
HoxFU (4.9 pmol) was incubated with 25 µM NADH at two different O2 concentrations. Superoxide production was measured spectrophotometrically on the basis of hydroxylamine oxidation.
b
One Unit of superoxide dismutase (SOD) is defined as the amount of SOD required to inhibit the rate of xanthine oxidase-mediated reduction of cytochrome c by 50% [17]. Values represent the arithmetic means and standard deviations of three independent experiments.