Penner M H, Yamasaki R B, Osuga D T, Babin D R, Meares C F, Feeney R E
Arch Biochem Biophys. 1983 Sep;225(2):740-7. doi: 10.1016/0003-9861(83)90085-1.
Periodate treatments of apo human serum transferrin (HST), and apo chicken ovotransferrin (COT) were previously reported to cause a rapid loss of Fe+3 binding capacity, with a loss of 3 to 5 tyrosine residues [P. AZARI AND J. L. PHILLIPS (1970) Arch. Biochem. Biophys. 138, 32-38; K. F. GEOGHEGAN, J. L. DALLAS, AND R. E. FEENEY (1980) J. Biol. Chem. 255, 11429-11434]. The effects of periodate and hydrogen peroxide on human lactotransferrin (HLT), HST, and COT have been compared. All three apotransferrins were rapidly inactivated and lost approximately 4 to 5 tyrosine residues by 5 mM periodate treatment; their iron complexes had little or no inactivation and losses of approximately 1 to 2 tyrosine residues. All three iron transferrins were highly resistant to inactivation by 5 mM periodate in bicarbonate, with or without the addition of phosphate, while in phosphate (with ambient carbonate) Fe2HLT was highly resistant, Fe2COT slightly less resistant, and Fe2HST much less resistant. Similar oxidations of methionines to the sulfoxides were found in both the apo and iron forms. After 150 min of 5 mM periodate treatment HST lost approximately 3 (apo 3.1, iron 2.8) of 9, HLT approximately 3 (apo 2.6, iron 2.9) of 6, and COT approximately 7 (apo 7.2, iron 7.2) of 11 methionines per mole of protein. In the presence of 8 M urea HST had essentially all of its methionine residues oxidized by periodate, but only lost part of its activity on renaturation. Treatment of all apo transferrins with 300 mM hydrogen peroxide resulted in little or no losses (less than 10%) in activity. HST lost approximately one-third of its methionines and no tyrosines during the 300 mM hydrogen peroxide treatment. Therefore the essentiality of tyrosines for all three transferrins was confirmed and the nonessentiality of methionines was demonstrated.
先前有报道称，用高碘酸盐处理脱铁人血清转铁蛋白（HST）和脱铁鸡卵转铁蛋白（COT）会导致Fe+3结合能力迅速丧失，同时有3至5个酪氨酸残基丢失[P. AZARI和J. L. PHILLIPS（1970年）《生物化学与生物物理学报》138卷，32 - 38页；K. F. GEOGHEGAN、J. L. DALLAS和R. E. FEENEY（1980年）《生物化学杂志》255卷，11429 - 11434页]。已比较了高碘酸盐和过氧化氢对人乳铁蛋白（HLT）、HST和COT的影响。通过5 mM高碘酸盐处理，所有三种脱铁转铁蛋白均迅速失活，且大约有4至5个酪氨酸残基丢失；它们的铁复合物几乎没有失活，且大约有1至2个酪氨酸残基丢失。在碳酸氢盐中，无论是否添加磷酸盐，所有三种铁转铁蛋白对5 mM高碘酸盐的失活都具有高度抗性，而在磷酸盐（含环境碳酸盐）中，Fe2HLT具有高度抗性，Fe2COT抗性稍低，Fe2HST抗性则低得多。在脱铁和铁形式中均发现甲硫氨酸类似地氧化为亚砜。经过5 mM高碘酸盐处理150分钟后，每摩尔蛋白质中，HST的9个甲硫氨酸大约丢失3个（脱铁形式为3.1个，铁形式为2.8个），HLT的6个甲硫氨酸大约丢失3个（脱铁形式为2.6个，铁形式为2.9个），COT的11个甲硫氨酸大约丢失7个（脱铁形式为7.2个，铁形式为7.2个）。在8 M尿素存在的情况下，HST的所有甲硫氨酸残基基本上都被高碘酸盐氧化，但复性后仅丧失部分活性。用300 mM过氧化氢处理所有脱铁转铁蛋白后，活性几乎没有损失或损失极小（小于10%）。在300 mM过氧化氢处理过程中，HST大约有三分之一的甲硫氨酸丢失，且没有酪氨酸丢失。因此，证实了酪氨酸对所有三种转铁蛋白的必要性，并证明了甲硫氨酸的非必要性。
