Li Chaorui, Hu Xiaosong, Zhao Guanghua
Research Center of Fruit and Vegetable Processing, College of Food Science and Nutritional Engineering, China Agricultural University, Haidian District, Beijing, China.
Biochimie. 2009 Feb;91(2):230-9. doi: 10.1016/j.biochi.2008.09.008. Epub 2008 Oct 17.
It was established that ferritin from pea seed is composed of 26.5 and 28.0kDa subunits, but the relationship between the two subunits is unclear. The present study by both MALDI-TOF-MS and MS/MS indicated that the 28.0kDa subunit is distinct from the 26.5kDa subunit although they might share high homology in amino acid sequence, a result suggesting that pea seed ferritin is encoded by at least two genes. This result is not consistent with previous proposal that the 28.0kDa subunit is converted into the 26.5kDa subunit upon cleavage of its N-terminal sequence by free radical. Also, present results indicated that pea seed ferritin contains two different kinds of ferroxidase centers located in the 28.0 and 26.5kDa subunits, respectively. This is an exception among all known ferritins. Therefore, it is of special interest to know the role of the two subunits in iron oxidative deposition. Spectrophotometric titration and stopped flow results indicated that 48 ferrous ions can be bound and oxidized by oxygen at the ferroxidase sites, demonstrating that all of the ferroxidase sites are active and involved in fast Fe(II) oxidation. However, unlike H and L subunits in horse spleen ferritin (HoSF), both the 28.0 and 26.5 subunits lack cooperation in iron turnover into the inner cavity of pea seed ferritin.
已确定豌豆种子中的铁蛋白由26.5 kDa和28.0 kDa的亚基组成，但这两个亚基之间的关系尚不清楚。本研究通过基质辅助激光解吸电离飞行时间质谱（MALDI-TOF-MS）和串联质谱（MS/MS）表明，28.0 kDa亚基与26.5 kDa亚基不同，尽管它们在氨基酸序列上可能具有高度同源性，这一结果表明豌豆种子铁蛋白至少由两个基因编码。该结果与先前的提议不一致，即28.0 kDa亚基在被自由基切割其N端序列后会转化为26.5 kDa亚基。此外，目前的结果表明，豌豆种子铁蛋白分别在28.0 kDa和26.5 kDa亚基中含有两种不同类型的铁氧化酶中心。这在所有已知的铁蛋白中是个例外。因此，了解这两个亚基在铁氧化沉积中的作用具有特殊意义。分光光度滴定和停流结果表明，在铁氧化酶位点上，48个亚铁离子可以被氧气结合并氧化，这表明所有的铁氧化酶位点都是活跃的，并且参与快速的Fe（II）氧化。然而，与马脾铁蛋白（HoSF）中的H和L亚基不同，28.0和26.5亚基在豌豆种子铁蛋白内腔中铁周转过程中缺乏协同作用。
