Inhibitory action of carbodiimides on bacterial membrane ATPase

Evidence for bidirectional formic acid translocation in vivo via the Escherichia coli formate channel FocA

Pentameric FocA permeates either formate or formic acid bidirectionally across the cytoplasmic membrane of anaerobically growing Escherichia coli. Each protomer of FocA has its own hydrophobic pore, but it is unclear whether formate or neutral formic acid is translocated in vivo. Here, we measured total and dicyclohexylcarbodiimide (DCCD)-inhibited proton flux out of resting, fermentatively grown, stationary-phase E. coli cells in dependence on FocA. Using a wild-type strain synthesizing native FocA, it was shown that using glucose as a source of formate, DCCD-independent proton efflux was ∼2.5 mmol min-1, while a mutant lacking FocA showed only DCCD-inhibited, FOF1-ATPase-dependent proton-efflux. A strain synthesizing a chromosomally-encoded FocAH209N variant that functions exclusively to translocate formic acid out of the cell, showed a further 20 % increase in FocA-dependent proton efflux relative to the parental strain. Cells synthesizing a FocAT91A variant, which is unable to translocate formic acid out of the cell, showed only DCCD-inhibited proton efflux. When exogenous formate was added, formic acid uptake was shown to be both FocA- and proton motive force-dependent. By measuring rates of H2 production, potassium ion flux and ATPase activity, these data support a role for coupling between formate, proton and K+ ion translocation in maintaining pH and ion gradient homeostasis during fermentation. FocA thus plays a key role in maintaining this homeostatic balance in fermenting cells by bidirectionally translocating formic acid.

Effect of Bioactive Primers on Bacterial-Induced Secondary Caries at the Tooth-Resin Interface

Secondary caries at the tooth-resin interface is the primary reason for replacement of resin composite restorations. The tooth-resin interface is formed by the interlocking of resin material with hydroxyapatite crystals in enamel and collagen mesh structure in dentin. Efforts to strengthen the tooth-resin interface have identified chemical agents with dentin collagen cross-linking potential and antimicrobial activities. The purpose of the present study was to assess protective effects of bioactive primer against secondary caries development around enamel and dentin margins of class V restorations, using an in vitro bacterial caries model. Class V composite restorations were prepared on 60 bovine teeth (n=15) with pretreatment of the cavity walls with control buffer solution, an enriched fraction of grape seed extract (e-GSE), 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide/N-hydroxysuccinimide, or chlorhexidine digluconate. After incubating specimens in a bacterial model with Streptococcus mutans for four days, dentin and enamel were assessed by fluorescence microscopy. Results revealed that only the naturally occurring product, e-GSE, significantly inhibited the development of secondary caries immediately adjacent to the dentin-resin interface, as indicated by the caries inhibition zone. No inhibitory effects were observed in enamel margins. The results suggest that the incorporation of e-GSE into components of the adhesive system may inhibit secondary caries and potentially contribute to the protection of highly vulnerable dentin-resin margins.

The effects of copper (II) ions on Enterococcus hirae cell growth and the proton-translocating FoF1 ATPase activity

Enterococcus hirae grow well under anaerobic conditions at alkaline pH (pH 8.0) producing acids by glucose fermentation. Bacterial growth was shown to be accompanied by decrease of redox potential from positive values (approximately +35 mV) to negative ones (approximately -220 mV). An oxidizer copper (II) ions (Cu(2+)) affected bacterial growth in a concentration-dependent manner (within the range of 0.05 mM to 1 mM) increasing lag phase duration and decreasing specific growth rate. These effects were observed with the wild-type strain ATCC9790 and the atpD mutant strain MS116 (with absent beta subunit of F(1) of the F(o)F(1) ATPase) both. Also ATPase activity and proton-potassium ions exchange were assessed with and without N,N'-dicyclohexylcarbodiimide (DCCD), inhibitor of the F(o)F(1) ATPase. In both cases (DCCD +/-), even low Cu(2+) concentrations had noticeable effect on ATPase activity, but with less visible concentration-dependent manner. Changes in the number of accessible SH-groups were observed with E. hirae ATCC9790 and MS116 membrane vesicles. In both strains Cu(2+) markedly decreased the number of SH-groups in the presence of K(+) ions. The addition of ATP increased the amount of accessible SH-groups in ATCC9790 and decreased this number in MS116; Cu(2+) blocked ATP-installed increase in SH-groups number in ATCC9790. H(+)-K(+)-exchange of bacteria was markedly inhibited by Cu(2+), but stronger effects were detected together with DCCD. Moreover, discrimination between Cu(2+) and other bivalent cation--Ni(2+) was shown. It is suggested that Cu(2+) ions inhibit E. hirae cell growth by direct affect on the F(o)F(1) ATPase leading to conformational changes in this protein complex and decrease in its activity.

Antituberculosis drugs: ten years of research

Tuberculosis is today amongst the worldwide health threats. As resistant strains of Mycobacterium tuberculosis have slowly emerged, treatment failure is too often a fact, especially in countries lacking the necessary health care organisation to provide the long and costly treatment adapted to patients. Because of lack of treatment or lack of adapted treatment, at least two million people will die of tuberculosis this year. Due to this concern, this infectious disease was the focus of renewed scientific interest in the last decade. Regimens were optimized and much was learnt on the mechanisms of action of the antituberculosis drugs used. Moreover, the quest for original drugs overcoming some of the problems of current regimens also became the focus of research programmes and many new series of M. tuberculosis growth inhibitors were reported. This review presents the drugs currently used in antituberculosis treatments and the most advanced compounds undergoing clinical trials. We then provide a description of their mechanism of action along with other series of inhibitors known to act on related biochemical targets. This is followed by other inhibitors of M. tuberculosis growth, including recently reported compounds devoid of a reported mechanism of action.

Properties of the N,N'-dicyclohexylcarbodiimide resistant ATPase of Streptococcus cremoris

1. The specific activity of the membrane-bound ATPase of Streptococcus cremoris HA was 1.30 mumol Pi/mg protein/min. 2. Km for ATP as substrate was 0.8 mM. 3. The pH optimum was 8.0 at +37 degrees C. 4. The ATPase was maximally activated with Mg2+/ATP molar ratio of 1:2. 5. Cations activated the enzyme in order: Mg2+ greater than Co2+ greater than Mn2+ greater than Zn2+ greater than Ca2+ greater than K+ greater than Na+. 6. The enzyme was inhibited by oligomycin (27-77%), sodium azide (13-33%) and ouabain (15-22%). N,N'-dicyclohexylcarbodiimide had no effect on the enzyme activity.

In vivo and in vitro incorporation of endogenous nucleotides by the energy-transducing ATPase of Streptococcus faecalis

The soluble ATPase isolated from Streptococcus faecalis membranes containing tightly bound endogenous nucleotides do not exchange in the presence of ATP and Mg+2 added during the purification of the enzyme. In this paper the stoichiometry of endogenous nucleotides in the soluble ATPase obtained from (a) growing cells, (b) nongrowing glycolyzing cells, and (c) isolated cell membranes has been defined. The time course of incorporation was also studied in nongrowing, glycolyzing cells and isolated cell membranes. In all cases, 1-2 mol of nucleotide was bound per mol of enzyme. Maximal incorporation required approximately 1 h at 38 degrees C. Incorporation of cytoplasmic nucleotide into the enzyme occurred by a process of slow exchange for bound nucleotide. N,N'-dicyclohexylcarbodiimide, which inhibits the membrane-bound ATPase and prevents generation of the protonmotive force, had no effect on incorporation of endogenous nucleotides in glycolyzing cells. Treatment of glycolyzing cells with gramicidin D plus K+, which dissipates the protonmotive force but has no effect on ATPase activity, did not inhibit incorporation of nucleotide. These results support the view that the slow exchange-incorporation of endogenous nucleotide(s) is independent of ATP hydrolysis and a protonmotive force. An in vitro system for the study of nucleotide binding at endogenous sites is described.

The effects of carbodiimides on functions associated with the energy-conservation mechanism in beef heart sub-mitochondrial particles

N,N'-di-n-propyl-, N,N'di-n-butyl-, N,N'-di-n-pentyl-, N,N'di-n-hexyl-, N,N'di-n-octoyl, N,N'-dibenzhydryl-, and N,N'-dibenzhydrylcarbodiimides were synthesized. They were all effective inhibitors (2 nmoles carbodiimide per milligram protein) of the ATP-driven reduction of NAD by succinate and the ATP-driven transhydrogenase activities catalyzed by beef heart submitochondrial particles (SMP). They had no effect on the nonenergy-linked transhydrogenase and stimulated the succinate-driven aerobic transhydrogenase activity of beef heart SMP. It was concluded that they exert their effects by reacting with the N,N'-dicyclohexylcarbodiimide-binding protein. Water-soluble carbodiimides were not effective inhibitors.

Membrane ATPase of Bacillus subtilis. I. Purification and properties

The membrane ATPase (EC 3.6.1.3) of Bacillus subtilis can be solubilized by a shock-wash process. Two procedures for purifying the solubilized enzyme are reported. A protease inhibitor, phenylmethane sulfonylfluoride, was introduced in the solubilization and purification step. The resultant ATPase purified by density gradient centrifugation has a molecular weight of 315 000, an s20,w of 13,4 and an amino acid composition very similar to bacterial ATPases already studied. After exposure to polyacrylamide gel electrophoresis in presence of sodium dodecyl sulphate (SDS), or 8 M urea or SDS-urea, the purified ATPase can be dissociated in two non-identical subunits of molecular weights 59 000 (alpha) and 57 000 (beta) with different charges. Kinetic studies showed that Ca2+ or Zn2+ are required for ATPase activity, although Mg2+ was uneffective. At optimal Ca2+ concentration, the Mg2+ has an inhibitory effect. The Km for ATP is 1.3 mM. Inhibitors of the oxydative phosphorylation, of the mitochondrial ATPase and of the (Na+ + K+)-ATPase are studied.

Bacillus megaterium mutant deficient in membrane-bound adenosine triphosphatase activity

An adenosine triphosphatase (ATPase) mutant of Bacillus megaterium was isolated and characterized. This mutant (designated A37) was unable to grow on nonfermentable carbon sources and possessed less than 5% of the wild-type ATPase activity. Oxygen uptake by the mutant was comparable to that in the wild type. Sporulation in the wild type occurred in both glucose- and nitrogen-limiting media; however, A37 sporulated only in the nitrogen-limiting medium. The inability of A37 to sporulate in glucose-limiting medium seemed to be due to insufficient adenosine 5'-triphosphate (ATP) levels during the sporulation stages. Fructose, which can generate ATP via substrate-level phosphorylation, is equally efficient in stimulating ATP synthesis in the wild type and A37. Malate-stimulated ATP synthesis in the wild type was shown to have many characteristics associated with oxidative phosphorylation and was absent in the mutant. These data suggest that the ATPase deficiency results in the loss of oxidative phosphorylation.

Localization and possible role of an adenosine triphosphatase in Chlorobium thiosulfatophilum

1. Evidence is presented that the ATPase activity detected in cell extracts of Chlorobium thiosulfatophilum is bound to the cytoplasmic membrane rather than to the chlorobium vesicles. 2. The activity of this ATPase is inhibited in vitro by various carbodiimides, phloridzin and sodium azide. 3. The apparent Km for ATP is approximately 0.2 mM and the enzyme shows product inhibition by ADP. 4. Photophosphorylation, characterized in vivo, is inhibited by many of the compounds that inhibit the ATPase.

Effect of dicyclohexylcarbodiimide on growth and membrane-mediated processes in wild type and heptose-deficient mutants of Escherichia coli K-12

The effects of N,N'-dicyclohexylcarbodiimide (DCCD) on the growth of Streptococcus faecalis, and on the growth, beta-galactosidase synthesis, and various membrane-mediated processes, were studied in wild-type Escherichia coli JE1011 and its lipopolysaccharide-defective mutant NS1. DCCD (0.1 mM) completely inhibited the growth of S. faecalis and E. coli NS1 but had little effect on strain JE1011. The same amount of DCCD with E. coli NS1, but not with E. coli JE1011, inhibited the induction of beta-galactosidase, increased the permeability of the cells to o-nitrophenyl-beta-d-galactoside without causing extensive cell lysis or release of ultraviolet-absorbing materials, and inhibited the oxidation of certain intermediates of the tricarboxylic acid cycle. Inhibition of the oxidation of malate, fumarate, and alpha-ketoglutarate by DCCD appeared to be at the level of the transport system for these compounds. Inhibition of the membrane-bound adenosine triphosphatase by DCCD was not entirely responsible for these effects, since oxidation of these substances, and transport of [(14)C]succinate and [(14)C]fumarate, was inhibited by DCCD in a mutant, N(144), which lacked adenosine triphosphatase activity. It is concluded that lipopolysaccharide forms a barrier to DCCD in wild-type E. coli, and that DCCD can inhibit several processes in the cell.

Conservation and transformation of energy by bacterial membranes

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