Department of Environmental and Occupational Health, Rutgers University School of Public Health, Piscataway, NJ 08854, United States.
Department of Pharmacology and Toxicology, Ernest Mario School of Pharmacy, Rutgers University, Piscataway, NJ 08854, United States.
Toxicol Appl Pharmacol. 2018 Nov 15;359:102-107. doi: 10.1016/j.taap.2018.09.011. Epub 2018 Sep 15.
NADH cytochrome b reductase mediates electron transfer from NADH to cytochrome b utilizing flavin adenine dinucleotide as a redox cofactor. Reduced cytochrome b is an important cofactor in many metabolic reactions including cytochrome P450-mediated xenobiotic metabolism, steroid biosynthesis and fatty acid metabolism, hemoglobin reduction, and methionine and plasmalogen synthesis. Using recombinant human enzyme, we discovered that cytochrome b5 reductase mediates redox cycling of a variety of quinones generating superoxide anion, hydrogen peroxide, and, in the presence of transition metals, hydroxyl radicals. Redox cycling activity was oxygen-dependent and preferentially utilized NADH as a co-substrate; NADH was 5-10 times more active than NADPH in supporting redox cycling. Redox cycling activity was greatest for 9,10-phenanthrenequinone and 1,2-naphthoquinone, followed by 1,4-naphthoquinone and 2-methyl-1,4-naphthoquinone (menadione), nitrofurantoin and 2-hydroxyestradiol. Using menadione as the substrate, quinone redox cycling was found to inhibit reduction of cytochrome b by cytochrome b reductase, as measured by heme spectral changes in cytochrome b. Under anaerobic conditions where redox cycling is inhibited, menadione had no effect on the reduction of cytochrome b. Chemical redox cycling by cytochrome b reductase may be important in generating cytotoxic reactive oxygen species in target tissues. This activity, together with the inhibition of cytochrome b reduction by redox-active chemicals and consequent deficiencies in available cellular cytochrome b, are likely to contribute to tissue injury following exposure to quinones and related redox active chemicals.
NADH 细胞色素 b 还原酶利用黄素腺嘌呤二核苷酸作为氧化还原辅助因子，将电子从 NADH 转移到细胞色素 b。还原型细胞色素 b 是许多代谢反应中的重要辅酶，包括细胞色素 P450 介导的外来化合物代谢、类固醇生物合成和脂肪酸代谢、血红蛋白还原以及蛋氨酸和磷脂酰醇合成。使用重组人酶，我们发现细胞色素 b5 还原酶介导多种醌的氧化还原循环，产生超氧阴离子、过氧化氢，并且在过渡金属存在下，产生羟基自由基。氧化还原循环活性依赖于氧气，并且优先利用 NADH 作为辅助底物；NADH 比 NADPH 更有效地支持氧化还原循环。9,10-菲醌和 1,2-萘醌的氧化还原循环活性最大，其次是 1,4-萘醌和 2-甲基-1,4-萘醌（维生素 K3）、呋喃妥因和 2-羟基雌二醇。使用维生素 K3 作为底物，发现醌的氧化还原循环抑制细胞色素 b 还原酶还原细胞色素 b，如细胞色素 b 血红素光谱变化所测量的。在抑制氧化还原循环的厌氧条件下，维生素 K3 对细胞色素 b 的还原没有影响。细胞色素 b 还原酶的化学氧化还原循环可能在靶组织中产生细胞毒性活性氧物种中很重要。这种活性，以及化学氧化还原活性物质对细胞色素 b 还原的抑制作用，以及随后细胞色素 b 可用性的缺陷，可能导致接触醌和相关氧化还原活性物质后组织损伤。
