Fluoridation

Maier, F. J.; Bellack, Ervin

doi:10.1080/10643387109381586

Cited by 10 publications

(4 citation statements)

References 35 publications

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“…In conclusion, a voltage sensitivity can be demonstrated in many types of porin reconstitution [4-7, 17, 18, 29, 371, but not so far in vivo. Nevertheless, permeability studies on porins in planar bilayers show excellent correlations with in vivo studies [7,[36][37][38][39][40][41] and justify the use of such techniques in the study of porin channels.…”

Section: Discussionmentioning

confidence: 99%

The voltage‐dependent activity of Escherichia coli porins in different planar bilayer reconstitutions

Lakey¹,

Pattus²

1989

European Journal of Biochemistry

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Because of conflicting results from differing techniques, the degree of voltage sensitivity of Escherichiu coli porins in planar bilayers is still a matter of debate. In order to provide the first comparative study, OmpF porin was purified in three ways; firstly as native outcr membrane vesicles, secondly as salt-extracted porin trimers in sodium dodecyl sulphate and thirdly as solubilised trimers extracted with octyl-polyoxyethylene (Octyl-POE). These methods represent the major approaches to porin isolation and purification. All three were reconstituted into Schindler-type bilayers. Detergent-solubilised OmpF was also reconstituted into Montal-Mueller-and Mueller-Rudin-type bilayers. In all cases voltage-dependent closing of OmpF was observed. Octyl-POE-extracted PhoE porin was similarly investigated in all three types of planar bilayer. Two membrane-formation techniques appeared genuinely to alter the voltage sensitivity of the porins they contained. Firstly, porins in membranes formed by the Montal-Mueller technique sometimes showed an increase in voltage sensitivity during the first 30 min after bilayer formation. Secondly, membranes formed by the Mueller-Rudin technique on thick polyethylene septa showed both poor solvent drainage and a significantly reduced porin voltage sensitivity. [4]. They showed that OmpF produced water-filled channels with limited selectivity between different ions and that the trimer conductance was around 2.0 nS in 1 M alkali metal chlorides. Bcnz and co-workers used the MuellerRudin ('black film' bilayer formation technique and showed that OmpF had an ohmic current/voltage relationship, indicating that the open state of these channels was not voltagesensitive. On the other hand, Schiiidler and Rosenbusch clearly demonstrated that the channels in their experiments could be closed by incrcasing the applied membranc potential difference. Since thcn published results on many porins have divided into two groups. One group, iiiostly using the socalled Schindler technique of bilaycr formation, show OmpF [5, 61, PhoE [7] and OmpC (our unpublished results) to be voltage-sensitive channels that close at potential differences above 100 mV. The other, much larger, group of publications shows porins in Mucller-Rudin bilayers to close only rarely and even then not because of an applied potential [l, 8 ~ 101 (for a review see [Ill).

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Section: Discussionmentioning

confidence: 99%

The voltage‐dependent activity of Escherichia coli porins in different planar bilayer reconstitutions

Lakey¹,

Pattus²

1989

European Journal of Biochemistry

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“…H 5 98C. As a result, a finer and more homogeneous structure was achieved, resulting in better mechanical properties [17][18][19].…”

Section: Resultsmentioning

confidence: 99%

Changes in the mechanical properties of laser-welded polymer specimens of polypropylene and polycarbonate through different sterilization procedures

Holl

Seul

2016

Polym Eng Sci

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Microorganisms on components should be killed through sterilization in order to ensure the safe use of medical products for patients. Therefore, polymer parts are treated particularly with gamma radiation, ethylene oxide, or superheated steam; such treatment may result in a modified structure or the degradation of the polymer. The present paper shall demonstrate how the mechanical properties of tension bars and welded samples of polypropylene and polycarbonate change during the sterilization procedure. The resulting changes in the structure and the degradation respectively will be analyzed by Fourier transform infrared spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) and structural property relationships shall be derived. The conducted analyses showed that the changes in the mechanical properties depend on the sample, the sterilization procedure, and the corresponding polymer; and that those changes must be considered when designing the respective products. POLYM. ENG. SCI.,

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“…Porins are either regulated in response to general growth conditions of temperature and osmolarity, like the OmpF and OmpC proteins of E. coli K-12, or they are induced in the presence or absence of a particular substrate. Thus, a maltodextrin-specific channel of E. coli [4,51, the 1 receptor, is induced by maltose [6] and a nucleoside-specific channel [7] is induced by nucleosides [8]. Likewise, phosphate starvation induces porins (PhoE porins) in E. coli [9], S. typhimurium [lo], Pseudomonas aeruginosa [l I] and a variety of other gram-negative bacteria [12].…”

mentioning

confidence: 99%

Pore formation by pho‐controlled outer‐membrane proteins of various Enterobacteriaceae in lipid bilayers

Bauer

Schmid

Boos

et al. 1988

European Journal of Biochemistry

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The structural genes of the PhoE porins of Klebsiella pneumonia, Enterobacter cloacae and Escherichia coli C, cloned in multicopy plasmids, were transfered into a porin-deficient E. coli K-12 strain, which was constitutive for the pho regulon, and the PhoE porins were isolated and purified. PhoE of Salmonella typhimurium could not be cloned but was isolated from a pho-constitutive strain. Reconstitution experiments with artificial lipid bilayer membranes showed that the different PhoE proteins formed pores exhibiting a single-channel conductance of about 200 pS at 0.1 M KC1. All PhoE porins formed anion-selective channels in KC1 at neutral pH. The degree of the selectivity was dependent on the PhoE species. The different PhoE porins formed general diffusion pores similar to the general porins but exhibited a considerable advantage for the permeation of phosphate through the outer membrane as compared to the constitutive OmpC and OmpF porins of E. coli K-12. [12]. The synthesis of PhoE makes sense because it has been shown that PhoE of E. coli K-12 forms anion-selective pores in vivo [13, 141 and in vitro [15, 161 and that of S . typhimurium in vitro [lo], whereas the general porins (OmpF and OmpC of E. coli K-12 and OmpF, OmpC and OmpD of S. typhimurium) are cation-selective [17].The study of the primary sequence of OmpF, OmpC and PhoE of E. coli K-12 via amino acid [18] or nucleotide sequence analysis [19-221 has shown that these pore-forming proteins have a high homology. The primary sequence of PhoE contains some additional lysines, which are most probably responsible for the anion selectivity of the pore-forming unit [20 -221. Porins form trimers of identical subunits and most of the polypeptide chain is in the form of an antiparallel P-pleated sheet [23]. PhoE genes of different enterobacterial species were cloned and expressed in E. coli K-12 [24]. Their primary sequences exhibit high homology. Their synthesis is regulated by a complicated regulatory system, thepho regulon Correspondence to R. Benz,

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Fluoridation

Cited by 10 publications

References 35 publications

The voltage‐dependent activity of Escherichia coli porins in different planar bilayer reconstitutions

The voltage‐dependent activity of Escherichia coli porins in different planar bilayer reconstitutions

Changes in the mechanical properties of laser-welded polymer specimens of polypropylene and polycarbonate through different sterilization procedures

Pore formation by pho‐controlled outer‐membrane proteins of various Enterobacteriaceae in lipid bilayers

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