Periplasmic space

Gram-negative organisms produce ced-bound P-lactamases which reside in the periplasmic space. Thus, for gram-negative bacteria, the antibiotic must penetrate the outer ced membrane/wad before coming in contact with a P-lactamase (80,139,140). 

Porin channels are impHcated in the transport of cephalosporins because ceds deficient in porins are much more impermeable than are ceds that are rich in porins. The porins appear to function as a molecular sieve, adowing molecules of relatively low molecular weight to gain access to the periplasmic space by passive diffusion. In enterobacteria, a clear correlation exists between porin quantity and cephalosporin resistance, suggesting that the outer membrane is the sole barrier to permeabdity. However, such a relationship is not clearly defined for Pseudomonas aeruginosa where additional barriers may be involved (139,144,146). 

Gram-negative bacteria are surrounded by two membranes, an inner plasma membrane and an outer membrane. These are separated by a periplasmic space. Most plasma membrane proteins contain long, continuous sequences of about 20 hydrophobic residues that are typical of transmembrane a helices such as those found in bacteriorhodopsin. In contrast, most outer membrane proteins do not show such sequence patterns. 

Figure 12.19 Schematic diagrams illustrating the arrangement of hacteriochlorophyll molecules in the light-harvesting complex LH2, viewed from the periplasmic space, (a) Eighteen hacteriochlorophyll molecules (green] are hound between the two rings of a (red) and p (blue) chains. The planes of these molecules are oriented perpendicular to the plane of the membrane and the molecules are bound close to the periplasmic space, (b) Nine hacteriochlorophyll molecules (green) are bound between the p chains (blue) with their planes oriented parallel to the plane of the membrane. These molecules are bound in the middle of the membrane.

FIGURE 22.17 The R. viridis reaction center is coupled to the cytochrome h/Cl complex through the quinone pool (Q). Quinone molecules are photore-duced at the reaction center Qb site (2 e [2 hv] per Q reduced) and then diffuse to the cytochrome h/ci complex, where they are reoxidized. Note that e flow from cytochrome h/ci back to the reaction center occurs via the periplasmic protein cytochrome co- Note also that 3 to 4 are translocated into the periplasmic space for each Q molecule oxidized at cytochrome h/ci. The resultant proton-motive force drives ATP synthesis by the bacterial FiFo ATP synthase. (Adapted from Deisenhofer, and Michel, H., 1989. The photosynthetic reaction center from the purple bac-terinm Rhod.opseud.omoaas viridis. Science 245 1463.)... 

Overexpression of apoaequorin (Inouye et al., 1989, 1991). To produce a large quantity of apoaequorin, an apoaequorin expression plasmid piP-HE containing the signal peptide coding sequence of the outer membrane protein A (ompA) of E. coli (Fig. 4.1.12) was constructed and expressed in E. coli. The expressed apoaequorin was secreted into the periplasmic space of bacterial cells and culture medium. The cleaving of ompA took place during secretion thus the... 

An improved method of producing recombinant aequorin was devised based on the fact that the expression of the peak amount of apoaequorin in bacterial cells occurs several hours before the secretion into culture medium (Shimomura and Inouye, 1999). The cells containing apoaequorin in the periplasmic space, before secretion, are extracted under a very mild condition and, at the same time, converted into aequorin. The purification of the extract by two steps of column chromatography yields a high-purity preparation of recombinant aequorin. 

Previously, we have shown that functional secretion of OPH molecules into the periplasmic space induced about 2.8-fold higher specific whole cell OPH activity [10]. From the detail reaction kinetic studies in this work, we showed that this periplasmic space-secretion strategy provided much improved bioconversion capability and efficiency ( 1.8-fold) for Paraoxon as a model organophosphate compound. From these results, we confirmed that Tat-driven periplasmic secretion of OPH can be successfully employed to develop a whole cell biocatalysis system with notable enhanced bioconversion efficiency and capability for environmental toxic organophosphates. 

AGAC-modifying enzymes are active outside the cytoplasmic membrane, in the periplasmic space in Gram-negative bacteria and extracellularly in Gram-positives. Table 9.4 summarizes some of the enzymes involved in AGAC resistance and their spectrum of activity. 

The chlorate reductase has been characterized in strain GR-1 where it was found in the periplasm, is oxygen-sensitive, and contains molybdenum, and both [3Fe-4S] and [4Fe-4S] clusters (Kengen et al. 1999). The arsenate reductase from Chrysiogenes arsenatis contains Mo, Fe, and acid-labile S (Krafft and Macy 1998), and the reductase from Thauera selenatis that is specific for selenate, is located in the periplasmic space, and contains Mo, Fe, acid-labile S, and cytochrome b (Schroeder et al. 1997). In contrast, the membrane-bound selenate reductase from Enterobacter cloacae SLDla-1 that cannot function as an electron acceptor under anaerobic conditions contains Mo and Fe and is distinct from nitrate reductase (Ridley et al. 2006). 

Nagata Y, A Futamura, K Miyauchi, M Takagi (1999) Two different types of dehalogenases LinA and linB, involved in y-hexachlorocyclohexane degradation in Sphingomonas paucimobilis are localized in the periplasmic space without molecular processing. J Bacterial 181 5409-5413. 

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... 

To reach their target enzymes, (3-lactams must enter the bacterial cell and cross the periplasm. A bacterium that contains the gene for a (3-lactamase can contain thousands of copies of this enzyme within the periplasmic space. Hence the antibiotics are effectively neutralized by [3-lactamase-catalyzed hydrolysis to inert species. For example, penicillin is hydrolyzed to the inactive species penicilloic acid (Figure 8.13). 

Fig. 6.11 The distribution in periplasmic space of the major molybdenum (and copper) enzymes except nitrogenase. Note the types of substrate.

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