OUTER MEMBRANE OF SALMONELLA-TYPHIMURIUM - ACCESSIBILITY OF PHOSPHOLIPID HEAD GROUPS TO PHOSPHOLIPASE-C AND CYANOGEN-BROMIDE ACTIVATED DEXTRAN IN EXTERNAL MEDIUM
OUTER MEMBRANE OF SALMONELLA-TYPHIMURIUM - ACCESSIBILITY OF PHOSPHOLIPID HEAD GROUPS TO PHOSPHOLIPASE-C AND CYANOGEN-BROMIDE ACTIVATED DEXTRAN IN EXTERNAL MEDIUM
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DOI：
10.1021/bi00657a012
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发表时间：
1976-01-01
期刊：
影响因子：
2.9
通讯作者：
NIKAIDO, H
中科院分区：
文献类型：
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作者：
KAMIO, Y;NIKAIDO, H
用蜡样芽孢杆菌磷脂酶C或cnbr活化的葡聚糖处理鼠伤寒沙门氏菌的全细胞。如果磷脂酰乙醇胺头基团暴露在这些细胞外膜的外表面并可接近，预计这些基团将被前一种药物水解并与后一种药物共价偶联。对于产生S型或Rc型脂多糖的菌株，结果表明外表面不存在任何可接近的头基团。当菌株产生的外膜含有较少的完全脂多糖（Rd或Re型）和较少的蛋白质时，两种方法都清楚地显示出暴露的磷脂酰乙醇胺头基团的存在。这些数据可以通过假设S和Rc菌株的外膜要么在其内部小叶中包含所有磷脂分子，要么在其外表面具有完全覆盖头部基团的蛋白质来最容易地解释。在这两种模型中，Rd或Re突变体外膜蛋白数量的减少都会产生暴露磷脂头基团的膜。cnbr活化葡聚糖制备简单，在接近生理条件下反应效率高。作为一种非穿透性膜标记试剂，它的另一个优点是，由于它的大小，人们可以相当确信它的不渗透性，而大多数其他试剂的不渗透性仅取决于带电基团的存在。
Whole cells of S. typhimurium were treated with Bacillus cereus phospholipase C or with CNBr-activated dextran. If phosphatidylethanolamine head groups are exposed and accessible on the outer surface of the outer membrane of these cells, it was expected that these groups would be hydrolyzed by the former agent and become covalently coupled to the latter agent. With strains producing lipopolysaccharides of S or Rc type, results did not indicate the presence of any accessible head groups on the outer surface. With strains that produce outer membranes containing less complete lipopolysaccharides (Rd or Re type) and reduced amounts of proteins, both methods clearly showed the presence of exposed phosphatidylethanolamine head groups. These data can be most easily explained by assuming that the outer membrane of S and Rc strains either contains all phospholipid molecules in its inner leaflet or has proteins that completely cover up the head groups at its outer surface. In either model, the reduction in the amount of outer membrane proteins in Rd or Re mutants would produce membranes with exposed phospholipid head groups. CNBr-activated dextran can be easily prepared, and reacts with high efficiency under near-physiological conditions. Its additional advantage as a nonpenetrating membrane-labeling reagent is that one can be quite confident on its impermeability because of its size, in contrast with most other reagents whose presumed impermeability is dependent only on the presence of charged groups.