Bacterial membranes inner

I realize that I will have to skip the chapter on the mitochondria and oxidative phosphorylation which has been developed to such a high degree by Packer and others. This chapter is well known to everybody. Its further interpretation may have been facilitated by the finding that the bacterial membrane (inner membrane) functions in many ways like the mitochondrial membrane and that it can perform active transport. Mitchell s electrochemical model of oxidative phosphorylation has been greatly strengthened by studies on active transport of nutrients in bacterial strains, some of which have defective membrane ATPases. Heppel and his coworkers have provided us with some important guidelines based on experiments carried out by themselves as well as by other laboratories. 

Poly-(3-hydroxybutanoic acid) (PHB), belongs to the large family of poly-(hydroxyalkanoates) (PHAs), high molecular weight natural polymers produced by various microorganisms and stored in cell cytoplasm (200). Low molecular weight PHB, also present in bacteria and are primarily involved in transport of ions and DNA across inner bacterial membrane (201). PHB could be developed as a valuable biocompatible material with possible applications in gene delivery after cytotoxic, safety, and efficacy evaluations. 

TSome microbial pathogens have lectins that mediate bacterial adhesion to host cells or toxin entry into cells. The bacterium believed responsible for most gastric ulcers, Helicobacter pylori, adheres to the inner surface of the stomach by interactions between bacterial membrane lectins and specific oligosaccharides of membrane glycoproteins of the gastric epithelial cells... 

Membranes contain many largely a-helical proteins. Cell surface receptors often appear to have one, two, or several membrane-spanning helices (see Chapter 8). The single peptide chain of the bacterial light-operated ion pump bacteriorhodopsin (Fig. 23-45) folds back upon itself to form seven helical rods just long enough to span the bacterial membrane in which it functions.189 Photosynthetic reaction centers contain an a helix bundle which is formed from two different protein subunits (Fig. 23-31).190 A recently discovered a,a barrel contains 12 helices. Six parallel helices form an inner barrel and 6 helices antiparallel to the first 6 form an outer layer (see Fig. 2-29).191-193... 

Most of the proteins of mitochondria are encoded in nuclear DNA and are synthesized on cytoplasmic ribosomes. Mitochondria do not utilize proteins homologous to those of the bacterial Sec system but have their own set of transport proteins.603-605 These proteins, which include an outer membrane complex (Tom) and an inner membrane complex (Tim), are discussed in Chapter 18 (see Fig. 18-4). Perhaps these specialized mitochondrial proteins are needed because transport into the mitochondrial matrix is in an opposite direction to the transport out through bacterial membranes. 

Principles to stabilize lipid bilayers by polymerization have been outlined schematically in Fig. 4a-d. Mother Nature — unfamiliar with the radically initiated polymerization of unsaturated compounds — uses other methods to-stabilize biomembranes. Polypeptides and polysaccharide derivatives act as a type of net which supports the biomembrane. Typical examples are spectrin, located at the inner surface of the erythrocyte membrane, clathrin, which is the major constituent of the coat structure in coated vesicles, and murein (peptidoglycan) a macromolecule coating the bacterial membrane as a component of the cell wall. Is it possible to mimic Nature and stabilize synthetic lipid bilayers by coating the liposome with a polymeric network without any covalent linkage between the vesicle and the polymer One can imagine different ways for the coating of liposomes with a polymer. This is illustrated below in Fig. 53. 

However, it is already clear that the mechanisms responsible for membrane protein integration into the ER membrane and the inner bacterial membrane do place certain constraints on the allowable structures... 

Chloroplasts have an outer (host) membrane and an inner (bacterial) membrane. 

In the previous two sections we discussed the electrodeformation and electroporation of vesicles made of single-component membranes in water. In this section, we consider the effect of salt present in the solutions. The membrane response discussed above was based on data accumulated for vesicles made of phosphatidylcholines (PCs), the most abundant fraction of lipids in mammahan cells. PC membranes are neutral and predominantly located in the outer leaflet of the plasma membrane. The inner leaflet, as well as the bilayer of bacterial membranes, is rich in charged lipids. This raises the question as to whether the presence of such charged lipids would influence the vesicle behavior in electric fields. Cholesterol is also present at a large fraction in mammalian cell membranes. It is extensively involved in the dynamics and stability of raft-hke domains in membranes [120]. In this section, apart from considering the response of vesicles in salt solutions, we describe aspects of the vesicle behavior of fluid-phase vesicles when two types of membrane inclusions are introduced, namely cholesterol and charged lipids. 

The name uncouplers arose from their ability to separate respiration from ATP production. Even when ATP production is inhibited, the oxidation of carbohydrates, etc., can continue if an uncoupler is present. Although the uncouplers are biocides, in principle toxic to all life-forms, many valuable pesticides belong to this group. However, few of them are selective, and they have many target organisms. The inner mitochondrial membranes are their most important sites of action, but chloroplasts and bacterial membranes will also be disturbed. 

Bacterial membranes contain respiratory enzymes resembling those found in inner mitochondrial membrane (Haddock and Jones, 1977), which oxidize NADH to NAD+ and H20. C.freundi grown aerobically, possess a particularly active membrane-bound NADH-oxidase activity (1.0—1.5 pmol/min-mg of protein at 30°C. Since these membranes alone or in the presence of NAD+ do not oxidize substrates such as L-alanine, L-lactate, or ethanol, they act as indicators of the activity of lactate dehydrogenase, alanine dehydrogenase, or alcohol dehydrogenase ... 

Membrane surfaces facing a shaded area are cytosolic faces surfaces facing an unshaded area are exopiasmic faces. Endocytosis of a bacterium by an ancestral eukaryotic cell would generate an organelle with two membranes, the outer membrane derived from the eukaryotic plasma membrane and the inner one from the bacterial membrane. The Fi subunit of... 

ATP synthase, localized to the cytosolic face of the bacterial membrane, would then face the matrix of the evolving mitochondrion (left) or chloroplast (right). Budding of vesicles from the inner chloroplast membrane, such as occurs during development of chloroplasts in contemporary plants, would generate the thyiakoid vesicles with the Fi subunit remaining on the cytosolic face, facing the chloroplast stroma. 

Additional work with closed vesicles derived from B. megaterium membranes demonstrates that NBD analogs of PE, PG, and PC can translocate across the membrane with a /i/2 of 30 s at 37°C (S. Hraffnsdottir, 1997). Similar types of experiments conducted with closed vesicles isolated from E. coli inner membrane reveal that NBD phospholipids traverse the bilayer with a of 7 min at 37°C (R. Huijbregts, 1996). This latter process is insensitive to protease and A-ethylmaleimide treatments and does not require ATP. Collectively, the data indicate that transbilayer lipid movement is rapid and does not require metabolic energy in bacterial membranes that harbor the biosynthetic enzymes for phospholipids. The basic characteristics of lipid translocation in the intact cell appear to be retained in isolated membranes. 

The polymer efficiently permeabilises anionic vesicles with compositions which mimic those of bacterial membranes. The polymer binds to anionic phospholipid vesicles but not zwitterionic vesicles, which causes phase separation in anionic phospholipid mixtures, clustering the negative charge. The polymer permeabilises the outer membrane of Escherichia coli ML-35p in a biphasic manner low polymer concentrations permeabilise the inner membrane of Escherichia coli ML-35p, whereas high concentrations of the polymer can block the active transport of or onitrophenyl-P-n-galactoside in wild-type Escherichia coli K12 [17]. 

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