Laboratory of Food Chemistry, Wageningen University, Wageningen, The Netherlands.
J Agric Food Chem. 2011 Jan 12;59(1):444-9. doi: 10.1021/jf104298y. Epub 2010 Dec 16.
The peroxidase-mediated oxidation of calcium-depleted bovine α-lactalbumin generates a mixture of covalently bound protein oligomers with interesting foaming properties. Here, we isolated the initially formed covalent α-lactalbumin dimer and studied its mode of cross-linking. Liquid chromatography-Fourier transform mass spectrometry (LC-FTMS) of proteolytic digests revealed the unambiguous identification of a peroxidase-catalyzed covalent link between Tyr18 and Tyr50. This shows that, although the radical reaction is often regarded as a random reaction, the initial product formation is specific. Protein structural modeling indicates that the conjugation reaction between these tyrosines is sterically favored and involves initial noncovalent protein complex formation through charge compensation, facilitating intermolecular cross-linking. The identification of the Tyr18-Tyr50 cross-link supports the view that the peroxidase-mediated oxidation of apo α-lactalbumin is a sequential process, involving the formation of linear trimers and higher order oligomers.
钙缺失牛α-乳白蛋白在过氧化物酶介导下发生氧化，生成具有有趣泡沫性质的共价结合蛋白低聚物混合物。在这里，我们分离出最初形成的共价α-乳白蛋白二聚体，并研究了其交联方式。经蛋白酶消化的液相色谱-傅里叶变换质谱（LC-FTMS）分析揭示了过氧化物酶催化的 Tyr18 和 Tyr50 之间共价键的明确鉴定。这表明，尽管自由基反应通常被认为是随机反应，但初始产物的形成是特异性的。蛋白质结构建模表明，这些酪氨酸之间的缀合反应在空间上是有利的，并且涉及通过电荷补偿的初始非共价蛋白质复合物形成，从而促进分子间交联。Tyr18-Tyr50 键的鉴定支持了这样一种观点，即脱辅基α-乳白蛋白的过氧化物酶介导氧化是一个顺序过程，涉及线性三聚体和更高阶低聚物的形成。
