FRAGMENTATION STUDIES OF SIALYLATED OLIGOSACCHARIDES

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 为了用串联质谱仪(MS)分析天然多聚糖，最好选择使指示分支位置的交叉环裂解丰度最大化的条件。最近，负离子串联质谱仪已被证明与正离子模式相比，在多糖中产生显著更高的此类离子丰度。以前的大部分工作都涉及到去唾液酸聚糖中的碎裂模式。本工作利用负模串联质谱仪对牛乳低聚糖和N-糖链的临界跨环裂解离子的丰度进行了比较。作为比较，研究了去质子化和硝化形成的去质子化离子和唾液酸化聚糖形成的去质子化离子和产物离子。击穿图谱清楚地表明，需要更多的能量来粉碎唾液酸化化合物，其程度与它们的sialo或硝酸盐加成化合物相同。在电离过程中从环羟基中提取质子可以定性地被视为给予离子的能量比从含有酸性基团的分子中提供的能量多得多，因此酸性多糖在气相中更稳定，因为负电荷存在于羧基上。这些结果具有很强的实际意义，因为从哺乳动物蛋白质中释放出的大部分多糖将被唾液酸化。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. For the analysis of native glycans using tandem mass spectrometry (MS), it is desirable to choose conditions whereby abundances of cross-ring cleavages indicative of branch positions are maximized. Recently, negative ion tandem mass spectrometry has been shown to produce significantly higher abundances of such ions in glycans compared to the positive ion mode. Much of this prior work has concerned fragmentation patterns in asialo glycans. The present work compares the abundances of critical cross-ring cleavage ions using negative mode tandem mass spectrometry for milk oligosaccharides and N-linked glycans. For comparison, product ion formation was studied for deprotonated and nitrated ions formed from asialo glycans and deprotonated ions from sialylated glycans. Breakdown profiles demonstrate clearly that more energy was required to fragment sialylated compounds to the same extent as either their asialo or nitrate adducted counterparts. The extraction of a proton from a ring hydroxyl group during the ionization process may be viewed, qualitatively, as imparting significantly more energy to the ion than would that from a molecule bearing an acidic group, so that acidic glycans are more stable in the gas phase, as the negative charge resides on the carboxyl group. These results have strong practical implications because a major portion of glycans released from mammalian proteins will be sialylated.