Open AccessCell Envelope and Shape of Escherichia coli K12
Author(s) -
Henning Ulf,
Höhn Barbara,
Sonntag Ingeborg
Publication year - 1973
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1973.tb03099.x
Subject(s) - cell envelope , bacterial outer membrane , cytoplasm , inner membrane , escherichia coli , membrane , cell wall , membrane protein , biochemistry , integral membrane protein , biology , molecular mass , trypsin , gel electrophoresis , peptidoglycan , cell membrane , phospholipid , band 3 , biophysics , enzyme , gene
Rod‐shaped “ghosts” can be isolated from Escherichia coli (and a number of other gram‐negative organisms) which are devoid of murein, are surrounded by a unit membrane and have lost all intracellular material except for some internal membrane which is derived from the cytoplasmic membrane. Ghosts consist of about 25% phospholipid, 25–30% lipopolysaccharide and 45–50% protein. Dodecylsulfate‐gel electrophoresis resolves the protein into four main bands with the apparent molecular weights: I, 40000, II, 28000, III, 18000 and IV, 10000. The proteins of all four bands are predominantly located in the outer membrane of the cell wall. Band IV has been identified as the lipoprotein, part of which is bound covalently to murein [1]. Band II very likely represents a homogeneous polypeptide chain and is derived by the action of trypsin on ghosts from a protein II* which has a molecular weight of about 40000. The molar ratio of polypeptides I, II* and IV in ghosts is about 1:1:8–10. Protein of band III is present in smaller amounts which, in contrast to I, II* and IV, were found to vary from preparation to preparation. Proteins I, II* and IV comprise 7–10% of the total cellular protein and they are most likely arranged in the outer membrane of the cell envelope as repeating subunits. Several lines of evidence indicate that proteins of all four bands are also present in the cytoplasmic membrane, although in considerably lower quantities than in the outer membrane. The synthesis of these cell wall proteins does not require DNA or murein synthesis. The phospholipid in ghosts is not required for their macroscopic structural integrity or for the unit membrane appearance of either of their membrane systems. A phospholipid bilayer is therefore not the basic structure of the ghost membranes.