Beale D, Fazakerley J K
Biochim Biophys Acta. 1981 Sep 29;670(2):230-5. doi: 10.1016/0005-2795(81)90014-3.
The action of trypsin at 55 degree C and pH 8.3 on pig IgM anti-Salmonella has been compared with the action of pepsin at 37 degree C and pH 4.6. Both processes cause the gradual removal of Fab arms and Cmu2 domains to produce eventually an (Fc)5 fragment. However, during tryptic digestion Fab arms are preferentially removed from the same subunit, whereas peptic digestion causes random removal from any subunit. At intermediate stages of digestion both processes produce partially fragmented molecules which consist of an (Fc)5 portion still attached to limited numbers of Fab arms. Both processes cause a gradual decrease in the ability of molecules to agglutinate Salmonella, but complement fixation by the complexes declines much more rapidly. A stage is reached where molecules having four Fab arms can still agglutinate but there is no complement fixation. However, the remaining arms on the tryptic molecules are distributed in pairs on the same subunit, whereas those on the peptic molecules are distributed randomly. Hence the number of remaining Fab arms, rather than their distribution, appears to be the critical factor which influences biological activity. A possible explanation for this is discussed.
已将胰蛋白酶在55摄氏度和pH 8.3条件下对猪抗沙门氏菌IgM的作用与胃蛋白酶在37摄氏度和pH 4.6条件下的作用进行了比较。这两个过程都会导致Fab臂和Cmu2结构域逐渐去除，最终产生一个(Fc)5片段。然而，在胰蛋白酶消化过程中，Fab臂优先从同一亚基上被去除，而胃蛋白酶消化则导致从任何亚基上随机去除。在消化的中间阶段，这两个过程都会产生部分片段化的分子，这些分子由一个仍与有限数量的Fab臂相连的(Fc)5部分组成。这两个过程都会导致分子凝集沙门氏菌的能力逐渐下降，但复合物的补体固定作用下降得更快。会达到这样一个阶段，即具有四个Fab臂的分子仍能凝集，但没有补体固定。然而，胰蛋白酶消化后的分子上剩余的臂在同一亚基上成对分布，而胃蛋白酶消化后的分子上的臂则随机分布。因此，剩余Fab臂的数量而非其分布似乎是影响生物活性的关键因素。对此进行了一个可能的解释。
