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三、蛋白质的化学降解~([1,2,3,4]) 在蛋白质一级结构的测定中,化学降解也是一个很重要的手段。一般化学降解的肽段都比较大,适合于在自动液相顺序仪中测定顺序,同时也有利于肽段次序的排列,但因肽段较大,分离困难,往往碰到不溶解和集聚等问题,产率也比较低。蛋白质化学降解常用的方法有。1.用溴化氰`~([5])(CNBr)降解蛋白质中的甲硫氨酸;2.用二甲基亚砜(DMSO)~([6])和卤氢酸等降解蛋白质中的色氨酸;3.用羟氨降解蛋白质中-Asn-Gly-结构;4.用稀酸~([?])部份降解蛋白质中Asp等。现在分述如下: (一)溴化氰降解用溴化氰降解蛋白质中的甲硫氨酸是化学降解中最常用的方法,特别是反应专一,产率比较高。又由于蛋白质中甲硫氨酸数目较少,因此降解后肽段数目也比较少,有利于肽段次序的排列。其反应机理如下:
Third, the chemical degradation of protein ~ ([1,2,3,4]) in the determination of the primary structure of the protein, chemical degradation is also a very important means. General chemical degradation of peptides are relatively large, suitable for automatic liquid-phase sequencer in determining the order, but also conducive to the arrangement of peptide sequences, but the larger peptides, separation difficulties, often encounter insolubilization and aggregation Problems, the yield is relatively low. Common methods of protein degradation are. 1. Degradation of methionine in proteins by cyanogen bromide- [5] (CNBr); 2. Degradation of proteins by dimethyl sulfoxide (DMSO) ~ ([6] Tryptophan; 3. hydroxylamine degradation of protein-Asn-Gly- structure; 4. with dilute acid ~ ([?]) Part of the degradation of protein Asp and so on. Now described as follows: (a) cyanogen bromide degradation with cyanogen bromide degradation of protein methionine is the most commonly used method of chemical degradation, especially the reaction-specific, the yield is relatively high. Since the number of methionine in the protein is small, the number of degraded peptides is relatively small, which is in favor of the arrangement of peptide sequences. The reaction mechanism is as follows: