Jones T, Spencer R, Walsh C
Biochemistry. 1978 Sep 19;17(19):4011-7. doi: 10.1021/bi00612a021.
Dihydroflavins reductively release iron rapidly and quantitatively from purified horse spleen or horse heart ferritin. The NAD(P)H:flavin oxidoreductase from Beneckea harveyi is used to generate a constant concentration of dihydroflavin permitting a continuous assay for complete iron release. Sepharose-linked dihydroflavins are not competent to release ferritin iron, demonstrating that the dihydroflavin must pass through the channels of the protein shell prior to iron reduction. Several experiments fail to show any specific flavin binding site, though dihydroflavins do display saturation kinetics with very high apparent Km's. The rates of iron release by a number of dihydroflavin analogues show that the electron transfer is significantly rate determining in iron release by dihydroriboflavin, while diffusion of the dihydroflavin through the protein channel is slow in the release of iron by dihydroFMN. The rate of iron release is also dependent on the initial content of iron, having a maximum at 1200 iron atoms per ferritin.
二氢黄素能快速且定量地从纯化的马脾或马心铁蛋白中还原释放铁。来自哈维氏贝内克氏菌的NAD(P)H：黄素氧化还原酶用于生成恒定浓度的二氢黄素，从而能够对铁的完全释放进行连续测定。与琼脂糖连接的二氢黄素无法释放铁蛋白中的铁，这表明二氢黄素在还原铁之前必须通过蛋白质外壳的通道。尽管二氢黄素确实表现出具有非常高表观Km值的饱和动力学，但多项实验未能显示出任何特定的黄素结合位点。多种二氢黄素类似物的铁释放速率表明，电子转移在二氢核黄素释放铁的过程中是显著的速率决定因素，而二氢黄素通过蛋白质通道的扩散在二氢黄素单核苷酸释放铁的过程中较慢。铁的释放速率还取决于铁的初始含量，每个铁蛋白含有1200个铁原子时达到最大值。
