Harrata A K, Domelsmith L N, Cole R B
Department of Chemistry, University of New Orleans, Lakefront, Louisiana 70148.
Biol Mass Spectrom. 1993 Jan;22(1):59-67. doi: 10.1002/bms.1200220108.
Negative ion and positive ion electrospray mass spectrometry have been employed to characterize the lipid A mixture produced by hydrolysis of lipopolysaccharides from Enterobacter agglomerans, a Gram-negative bacterium commonly found in field cotton. Neutral monophosphoryl lipid A molecules form stable anions via deprotonation, but adduct formation via cation attachment occurs in low yield. Dephosphorylated lipid A molecules, on the other hand, readily form adducts with Na+, whereas deprotonation occurs in low yield. The mass spectra of lipid A produced by E. agglomerans reveal the presence of lipid A ions which differ in the nature of attached fatty acid side chains. At least two heptaacyl forms of lipid A are present, one of which has a structure which appears to be the same as the structure of heptaacyl lipid A produced by Salmonella minnesota. The second structure differs only by the nature of the side chain at position 3' of the disaccharide backbone where a hydroxymyristoyloxymyristoyl group replaces the myristoyloxymyristoyl substituent. Collisionally activated dissociations prior to mass analysis enable the identification of fragment ions which can be distinguished from at least eight intact deprotonated molecules present in crude lipid A.
负离子和正离子电喷雾质谱已被用于表征由成团肠杆菌（一种常见于田间棉花的革兰氏阴性菌）的脂多糖水解产生的脂质A混合物。中性单磷酸化脂质A分子通过去质子化形成稳定的阴离子，但通过阳离子附着形成加合物的产率较低。另一方面，去磷酸化的脂质A分子很容易与Na+形成加合物，而去质子化的产率较低。成团肠杆菌产生的脂质A的质谱显示存在附着脂肪酸侧链性质不同的脂质A离子。至少存在两种七酰基形式的脂质A，其中一种的结构似乎与明尼苏达沙门氏菌产生的七酰基脂质A的结构相同。第二种结构的不同仅在于二糖主链3'位侧链的性质，其中一个羟基肉豆蔻酰氧基肉豆蔻酰基取代了肉豆蔻酰氧基肉豆蔻酰基取代基。在质量分析之前进行碰撞激活解离能够鉴定出可以与粗脂质A中存在的至少八个完整去质子化分子区分开的碎片离子。
