Badu-Boateng Charles, Pardalaki Sofia, Wolf Claude, Lajnef Sonia, Peyrot Fabienne, Naftalin Richard J
Cardiovascular Division, British Heart Foundation Centre of Research Excellence and Physiology Department, King's College London, 150 Stamford Street, London SE1 9NH, UK.
APLIPID Sarl, 75016 Paris, France.
Free Radic Biol Med. 2017 Jul;108:94-109. doi: 10.1016/j.freeradbiomed.2017.03.015. Epub 2017 Mar 21.
Ascorbate mobilizes iron from equine spleen ferritin by two separate processes. Ascorbate alone mobilizes ferritin iron with an apparent K ≈1.5mM. Labile iron >2μM, complexed with citrate (10mM), synergises ascorbate-dependent iron mobilization by decreasing the apparent K to ≈270μM and raising maximal mobilization rate by ≈5-fold. Catalase reduces the apparent K for both ascorbate and ascorbate+iron dependent mobilization by ≈80%. Iron mobilization by ascorbate alone has a higher activation energy (E=45.0±5.5kJ/mole) than when mediated by ascorbate with labile iron (10μM) (E=13.7±2.2kJ/mole); also mobilization by iron-ascorbate has a three-fold higher pH sensitivity (pH range 6.0-8.0) than with ascorbate alone. Hydrogen peroxide inhibits ascorbate's iron mobilizing action. EPR and autochemiluminescence studies show that ascorbate and labile iron within ferritin enhances radical formation, whereas ascorbate alone produces negligible radicals. These findings suggest that iron catalysed single electron transfer reactions from ascorbate, involving ascorbate or superoxide and possibly ferroxidase tyrosine radicals, accelerate iron mobilization from the ferroxidase centre more than EPR silent, bi-dentate two-electron transfers. These differing modes of electron transference from ascorbate mirror the known mono and bidentate oxidation reactions of dioxygen and hydrogen peroxide with di-ferrous iron at the ferroxidase centre. This study implies that labile iron, at physiological pH, complexed with citrate, synergises iron mobilization from ferritin by ascorbate (50-4000μM). This autocatalytic process can exacerbate oxidative stress in ferritin-containing inflamed tissue.
抗坏血酸盐通过两个独立过程从马脾铁蛋白中动员铁。单独的抗坏血酸盐以约1.5mM的表观K值动员铁蛋白铁。与柠檬酸盐（10mM）络合的>2μM不稳定铁通过将表观K值降低至约270μM并将最大动员速率提高约5倍来协同抗坏血酸盐依赖性铁动员。过氧化氢酶使抗坏血酸盐和抗坏血酸盐+铁依赖性动员的表观K值降低约80%。单独由抗坏血酸盐进行的铁动员比由抗坏血酸盐与不稳定铁（10μM）介导时具有更高的活化能（E=45.0±5.5kJ/摩尔）（E=13.7±2.2kJ/摩尔）；同样，抗坏血酸-铁介导的动员比单独抗坏血酸盐具有高三倍的pH敏感性（pH范围6.0-8.0）。过氧化氢抑制抗坏血酸盐的铁动员作用。电子顺磁共振（EPR）和自动化学发光研究表明，铁蛋白内的抗坏血酸盐和不稳定铁增强自由基形成，而单独的抗坏血酸盐产生可忽略不计的自由基。这些发现表明，涉及抗坏血酸盐或超氧化物以及可能的亚铁氧化酶酪氨酸自由基的抗坏血酸盐铁催化单电子转移反应，比EPR沉默的双齿双电子转移更能加速铁从亚铁氧化酶中心的动员。这些抗坏血酸盐不同的电子转移模式反映了亚铁氧化酶中心二价铁与氧气和过氧化氢已知的单齿和双齿氧化反应。这项研究表明，在生理pH值下，与柠檬酸盐络合的不稳定铁协同抗坏血酸盐（50-4000μM）从铁蛋白中动员铁。这种自催化过程会加剧含铁血蛋白的炎症组织中的氧化应激。
