This chapter discusses the molecular organization and structural role of outer membrane macromolecules. The outer membrane has been the subject of intensive research over the past two decades. During this time, the image of this layer has matured from a rather simple capsule-like girdle, the lipopolysaccharide (LPS) layer, to that of a sophisticated, unique and multifunctional membrane. A representative molecular model of a section of the outer membrane based on the data presented by several researchers is discussed in this chapter. LPS is a major constituent of the bacterial cell envelope, accounting for 3-8% of the dry weight of the cell. It is an amphipathic molecule consisting of a hydrophilic portion represented by the O-antigenic polysaccharide and core oligosaccharide linked to the glycolipidic Lipid A residue. The molecular weight of individual LPS molecules can vary from about 8000 to 54000 according to the lack or presence of variable numbers of the repeating saccharide units that comprise the O-antigenic polysaccharide.
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