Andrews S C, Treffry A, Harrison P M
Department of Biochemistry, University of Sheffield, U.K.
Biochem J. 1987 Jul 15;245(2):439-46. doi: 10.1042/bj2450439.
A minor electrophoretically fast component was found in ferritin from iron-loaded rat liver in addition to a major electrophoretically slow ferritin similar to that observed in control rats. The electrophoretically fast ferritin showed immunological identity with the slow component, but on electrophoresis in SDS it gave a peptide of 17.3 kDa, in contrast with the electrophoretically slow ferritin, which gave a major band corresponding to the L-subunit (20.7 kDa). Thus the electrophoretically fast ferritin resembles that reported by Massover [(1985) Biochim. Biophys. Acta 829, 377-386] in livers of mice with short-term parenteral iron overload. The electrophoretically fast ferritin had a lower iron content (2000 Fe atoms/molecule) than the electrophoretically slow ferritin (3000 Fe atoms/molecule). Removal and re-incorporation of iron was possible without effect on the electrophoretic mobility of either ferritin species. On subcellular fractionation the electrophoretically fast ferritin was enriched in pellet fractions and was the sole soluble ferritin isolated from iron-laden secondary lysosomes (siderosomes). The amount and relative proportion of the electrophoretically fast species increased with iron loading. Haemosiderin isolated from siderosomes was found to contain a peptide reactive to anti-ferritin serum and corresponding to the 17.3 kDa peptide of the electrophoretically fast ferritin species. Unlike the electrophoretically slow ferritin, the electrophoretically fast ferritin did not become significantly radioactive in a 1 h biosynthetic labelling experiment. We conclude that the minor ferritin is not, as has been suggested for mouse liver ferritin, 'a completely new species of smaller holoferritin that represents a shift in the ferritin phenotype' in response to siderosis, but a precursor of haemosiderin, in agreement with the proposal by Richter [(1984) Lab. Invest. 50, 26-35] concerning siderosomal ferritin.
除了一种电泳速度较慢的主要铁蛋白外，在铁负荷大鼠肝脏的铁蛋白中还发现了一种电泳速度较快的次要成分，这种主要铁蛋白与对照大鼠中观察到的类似。电泳速度较快的铁蛋白与速度较慢的成分具有免疫同一性，但在SDS中电泳时，它产生了一条17.3 kDa的肽段，这与电泳速度较慢的铁蛋白不同，后者产生了一条对应于L亚基（20.7 kDa）的主要条带。因此，电泳速度较快的铁蛋白类似于Massover [(1985) Biochim. Biophys. Acta 829, 377 - 386]报道的短期经肠外途径铁过载小鼠肝脏中的铁蛋白。电泳速度较快的铁蛋白的铁含量（2000个铁原子/分子）低于电泳速度较慢的铁蛋白（3000个铁原子/分子）。铁的去除和重新掺入是可能的，且不会影响任何一种铁蛋白的电泳迁移率。在亚细胞分级分离中，电泳速度较快的铁蛋白在沉淀级分中富集，并且是从富含铁的次级溶酶体（含铁小体）中分离出的唯一可溶性铁蛋白。电泳速度较快的铁蛋白的量和相对比例随着铁负荷的增加而增加。从含铁小体中分离出的血铁黄素被发现含有一种与抗铁蛋白血清反应的肽段，对应于电泳速度较快的铁蛋白的1 kDa肽段。与电泳速度较慢的铁蛋白不同，在1小时的生物合成标记实验中，电泳速度较快的铁蛋白没有明显的放射性。我们得出结论，这种次要铁蛋白并不像对小鼠肝脏铁蛋白所建议的那样，是“一种全新的较小全铁蛋白物种，代表了铁蛋白表型的转变”以响应铁沉着症，而是血铁黄素的前体，这与Richter [(1984) Lab. Invest. 50, 26 - 35]关于含铁小体铁蛋白的提议一致。
