Cell surfaces periplasmic space

Under normal conditions the sinusoidal endothelial cells are flat thin cells lying close against the hepatocyte surface, separated only by the periplasmic space. Cold preservation of the liver causes the endothelial cells to round up and detach, although they are not actually... 

In Gram-negative bacteria which are characterised by a rather complex cell envelope, the CM is also referred to as inner membrane to distinguish it from a second lipid bilayer, termed outer membrane (OM). The space between these two layers is called the periplasm (PP). In the periplasmic space, many proteins are found with a variety of functions. Some are involved in biosynthesis and/or export of cell wall components and surface structures (e.g. pili, flagellae,... 

The fatty acid chains are evidently embedded in the outer membrane as an anchor. About one-third of the lipoprotein molecules are attached covalently to the peptidoglycan through an amide linkage between the side chain amino group of the C-terminal lysine of the protein and a diaminopimelic acid residue of the peptidoglycan (Fig. 8-29). Thus, the protein replaces one of the terminal D-alanine residues of about one in ten of the murein peptides. There are 2.5 x 105 molecules of the bound form of the lipoprotein per cell spread over a surface area of peptidoglycan of 3 pm2. They appear to be associated as trimers located primarily in the periplasmic space.589... 

E. coli does not synthesize vitamin Bi2 and grows well without this nutrient. However, in certain circumstances there is a marginal benefit to the cell to be able to manufacture methionine by a pathway involving the vitamin. For this purpose the required apoprotein is synthesized, and the receptor protein is inserted in the membrane in anticipation of finding Bi2 in the environment (70). Phages BF23 and the E colicins have somehow managed to adapt to the Bi2 receptor (71). Besides the surface receptor, a second protein component in the periplasmic space may be necessary for further transport of the vitamin. 

This topic has been reviewed by Ingledew (55). The major components of the respiratory chain for T. ferrooxidans are a cytochrome oxidase of the Ci type, cytochromes c, and the blue copper protein rusticyanin. Initial electron transfer from Fe(II) to a cellular component takes place at the outer surface of the plasma membrane in the periplasmic space. The rate of electron transfer from Fe(II) to rusticyanin is too slow for rusticyanin to serve as the initial electron acceptor. Several proposals have been made for the primary site of iron oxidation. Ingledew (56) has suggested that the Fe(II) is oxidized by Fe(III) boimd to the cell wall the electron then moves rapidly through the polynuclear Fe(III) complex to rusticyanin or an alternative electron acceptor. Other proposals for the initial electron acceptor include a three-iron-sulfur cluster present in a membrane-bound Fe(II) oxidoreductase (39, 88), a 63,000 molecular weight Fe(II)-oxidizing enzyme isolated from T. ferrooxidans (40), and an acid-stable cytochrome c present in crude extracts of T. ferrooxidans (14). 

Based on the nature of the cytochromes, there are two kinds of photosynthetic bacterial reaction centers. The first kind, represented by that of Rhodobacter sphaeroides, has no tightly bound cytochromes. For these reaction centers, as shown schematically in Fig. 2, left, the soluble cytochrome C2 serves as the secondary electron donor to the reaction center the RC also accepts electrons from the cytochrome bc complex by way ofCytc2- The rate of electron transfer from cytochrome to the reaction center is sensitive to the ionic strength of the medium. Functionally, cytochrome C2 is positioned in a cyclic electron-transport loop. In Rb. sphaeroides, Rs. rubrum and Rp. capsulata cells, the two molecules of cytochromes C2 per RC are located in the periplasmic space between the cell wall and the cell membrane. When chromatophores are isolated from the cell the otherwise soluble cytochrome C2 become trapped and held by electrostatic forces to the membrane surface at the interface with the inner aqueous phase. These cytochromes electrostatically bound to the membrane can donate electrons to the photooxidized P870 in tens of microseconds at ambient temperatures, but are unable to transfer electrons to P870 at low temperatures. 

Figure 43-2. Beta-lactams and bacterial cell wall synthesis. The outer membrane shown in this simplified diagram is present only in gram-negative organisms. It is penetrated by proteins (porins) that are penrie-able to hydrophilic substances such as beta-lactam antibiotics. The peptidoglycan chains (mureins) are cross-linked by transpeptidases located in the cytoplasmic membrane, closely associated with penicillinbinding proteins (PBPs). Beta-lactam antibiotics bind to PBPs and inhibit transpeptidation, the final step in cell wall synthesis They also activate autolytic enzymes that cause lesions in the cell wall. Beta-lactamases, which inactivate beta-lactam antibiotics, may be present in the periplasmic space or on the outer surface of the cytoplasmic membrane. (Reproduced, with permission, from Katzung BG [editor]. Basic Clinical Pharmacology, 8th ed. McGraw-Hill, 2001.)...

The Gram-negative bacterium Escherichia coli is a versatile host and can be used both as a whole cell for biosensor purpose, if the sensing protein is made accessible to the pollutant by exposure on the bacterium surface, and as a factory to yield amounts of protein biomediator to be purified and assembled in a biosensor. The overetqtressed proteins in E. coli, depending on their target signals, can be transported to the outer cell and secreted in the cultivation medium or localised in distinct cell compartments. We intend as the outer cell of E. coli the extracellular space and the cell envelope, which consists of the outer membrane, the periplasm space and the cytoplasmic membrane. 

Many kinds of bacterial cells contain integrated protein complexes that take part in the respiratory electron-transport reaction in the cytoplasmic membrane. It is located near the cell surface beneath the cell wall, which is permeable to substances of relatively low molecular weights. Thus, oxidoreductases existing in the periplasmic space or bound to the cytoplasmic membrane may function as catalysts to oxidize or reduce substances outside the cells using externally added artificial electron acceptors or donors. A scheme of the bacterial cell catalysis is illustrated in Fig. 18. The rate (vceii) of the bacterial cell-catalyzed reaction can be written as (47)... 

In fact, the first degradative enzyme, chondroitin lyase, appears to be located in the periplasmic space between the inner and outer membranes of these gram negative organisms (13). Chondroitin lyase breaks chondroitin sulfate into disaccharides and these disaccharides are further degraded by enzymes which are located in the cytoplasm. None of these enzymes is membrane-bound. However there are probably some membrane proteins involved, e.g. receptors on the cell surface which bring the chondroitin sulfate into contact with the lyase and... 

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