FRAGMENTATION STUDIES OF SIALYLATED OLIGOSACCHARIDES

这个子项目是许多利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 对于使用串联质谱法（MS）分析天然聚糖，期望选择条件，由此使指示分支位置的交叉环裂解的丰度最大化。 最近，与正离子模式相比，负离子串联质谱已显示在聚糖中产生显著更高丰度的此类离子。 许多先前的工作都涉及脱唾液酸聚糖的断裂模式。 本工作比较了使用负模式串联质谱的牛奶低聚糖和N-连接聚糖的关键交叉环裂解离子的丰度。 为了进行比较，研究了脱唾液酸聚糖形成的去质子化和硝化离子以及唾液酸化聚糖形成的去质子化离子的产物离子形成。 击穿曲线清楚地表明，需要更多的能量来使唾液酸化化合物片段化到与它们的脱唾液酸盐或硝酸盐加合物对应物相同的程度。 在离子化过程中从环羟基提取质子可以定性地被视为比从带有酸性基团的分子向离子赋予显著更多的能量，使得酸性聚糖在气相中更稳定，因为负电荷驻留在羧基上。 这些结果具有很强的实际意义，因为从哺乳动物蛋白质释放的大部分聚糖将被唾液酸化。

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.