Department of Chemistry and Pharmacy, Food Chemistry, Emil Fischer Center, University of Erlangen-Nuremberg, Erlangen, Germany.
Proteomics. 2011 Feb;11(3):420-8. doi: 10.1002/pmic.201000233. Epub 2011 Jan 3.
Milk processing leads to severe protein damage caused by the formation of nonenzymatic posttranslational modifications (nePTMs), such as glycation and glycoxidation. As a result, the technological and nutritional function of milk proteins can be critically altered. The present study investigated the protein-specific distribution of the glycoxidation product N(ε) -carboxymethyllysine (CML) in the proteome of processed milk. For this purpose, raw milk and heated milk were separated by 1-D or 2-DE. The distribution of CML in the milk proteome was examined by immunoblotting. The changes in the protein composition that occurred during heating were monitored by Coomassie staining. Relative modification rates were measured for the major milk protein fractions after 30 and 60 min of heating at 120°C and normalized to the content of the respective protein fraction in the samples. The highest glycoxidation rates were detected in the high molecular weight aggregates that are generated during heating. The casein fraction and the whey protein β-lactoglobulin were affected in a similar manner. The relevance of the results for industrial milk processing was confirmed by analyzing several commercial milk products accordingly. The presented approach allows nonenzymatic posttranslational modification mapping of the entire milk proteome.
牛奶加工会导致严重的蛋白质损伤，这是由非酶翻译后修饰（nePTMs）形成引起的，例如糖化和糖基化。因此，牛奶蛋白质的技术和营养功能可能会受到严重影响。本研究调查了加工牛奶蛋白质组中糖基化产物 N(ε)-羧甲基赖氨酸（CML）的蛋白特异性分布。为此，通过 1-D 或 2-DE 将生奶和加热奶分离。通过免疫印迹法检查 CML 在牛奶蛋白质组中的分布。通过考马斯亮蓝染色监测加热过程中蛋白质组成的变化。在 120°C 加热 30 和 60 分钟后，对主要乳蛋白进行相对修饰率的测量，并根据样品中各蛋白的含量进行归一化。在加热过程中产生的高分子量聚集体中检测到最高的糖基化速率。酪蛋白和乳清蛋白β-乳球蛋白受到类似的影响。通过对相应的几种商业牛奶产品进行分析，验证了这些结果对工业牛奶加工的重要性。本研究提出的方法可用于对整个牛奶蛋白质组进行非酶翻译后修饰图谱绘制。
