- Volume 141, Issue 12, 1995
Volume 141, Issue 12, 1995
- Physiology And Growth
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Acetyl-CoA carboxylase activity in Helicobacter pylori and the requirement of increased CO2 for growth
More LessA biotinylated acetyl-CoA carboxylase from the microaerophilic bacterium Helicobacter pylori was partially purified and characterized. The approximate molecular mass of the native enzyme was estimated at 235 kDa by native PAGE. A single band corresponding to approximately 24 kDa was detected by SDS-PAGE, suggesting that the native enzyme is a multi-protein complex. The protein was isolated from the soluble fraction of the cell. Catalytic activity was acetyl-CoA-dependent and inhibited by avidin but unaffected by avidin pre-treated with excess biotin. The end-product of the reaction was identified as malonyl-CoA and the reaction was shown to be reversible by NMR spectroscopy. The activity of the enzyme was 0.29 μmol min-1 (mg protein)-1. The V max for bicarbonate was calculated at 0.73 μmol min-1 (mg protein)-1, and the affinity of the enzyme for this substrate was relatively low, with an apparent K m of 16.6 mM. These data provide the first evidence of a possible physiological role for the requirement of high levels of CO2 for growth in vitro of this bacterium.
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Starvation yields a drastic decrease in outer-membrane permeability to a periplasmic foreign protein in Myxococcus xanthus
More LessA recombinant Myxococcus xanthus strain was constructed that constitutively produces two proteins from Escherichia coli, the cytoplasmic -galactosidase and the periplasmic pH 2.5 acid phosphatase (AppA protein). We have previously shown that during vegetative growth, AppA protein is partly accumulated in the periplasm of M. xanthus and partly released into the medium. We demonstrate here that during starvation-induced development, release of periplasmic AppA protein to the medium did not occur over a period of 20 h. This was coincident with, but not caused by, the arrest of the synthesis of the foreign proteins. We have shown that this lack of secretion could be attributed to starvation per se and did not depend on the ability of the cells to undergo development. Our findings suggest that protein secretion which occurs during the first hours of starvation-induced development might therefore take place via a different route from that which occurs in vegetative cells.
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Adaptive response of Schizosaccharomyces pombe to hydrogen peroxide and menadione
More LessThe response of Schizosaccharomyces pombe to oxidative stresses has been examined. On challenging Schiz. pombe for 60 min at early exponential phase with either 40 mM H2O2 or 6 mM menadione (MD), a superoxide-generating agent, less than 10% of the cells survived. Pretreating Schiz. pombe cells with 0.2 mM H2O2 or 0.2 mM MD for 1 h significantly increased survival of these lethal doses of each oxidant, indicating the existence of an adaptive response to oxidative stress. Furthermore, cells pretreated with a low dose of MD became resistant to a lethal dose of H2O2. However, cells pretreated with H2O2 became only partially resistant to a lethal dose of MD. Adaptation was accompanied by the induction of several oxidative defence enzymes. The presence of 0/2 mM H2O2 induced catalase by 2.8-fold and peroxidase by 2.0-fold. The presence of 0.2 mM MD induced catalase by 2.0-fold, glucose-6-phosphate dehydrogenase by 1.9-fold, glutathione reductase by 2.7-fold, peroxidase by 3.0-fold, and superoxide dismutase (SOD) by 2.1-fold. The higher induction of these defence enzymes by MD may explain why MD-pretreated cells were better adapted to lethal doses of oxidants than H2O2-pretreated ones. All these enzymes except SOD and peroxidase increased more than 5.0-fold as cells proceeded into stationary phase. The GSH/GSSG ratio also increased by 60%. These changes accord with the observation that stationary phase cells survive oxidant treatment better than cells in vegetative growth.
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Porin and porin-associated protein (PAP) of Rhodospirillum rubrum FR1
More LessThe porin of Rhodospirillum rubrum FR1 was found in the outer membrane as a complex with a relatively small (32 kDa) porin-associated protein (PAP). The porin moiety of the complex consisted of a trimer which revealed a mainly β-sheet structure, while the porin-PAP complex also contained a significant α-helical portion. Isolated PAP exhibited a mostly α-helical structure. The porin-PAP complex had the same single-channel conductivity (2.8 nS) as the isolated porin, demonstrating that PAP did not affect the porin channel size. Differential extraction of the cell wall fraction with N,N-dimethyldodecylamine N-oxide revealed that PAP stabilized the porin in the outer membrane. EDTA caused dissociation of the porin-PAP complex, indicating that divalent cations were involved in formation of this complex.
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- Systematics
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Assignment of hitherto unidentified 16S rDNA species to a main line of descent within the domain Bacteria
More LessPhylogenetic analysis of the almost complete 16S rDNA sequence of the fimbriate prosthecate bacterium Verrucomicrobium spinosum confirms the unique phylogenetic position of this organism, as previously shown by oligonucleotide cataloguing and partial reverse transcriptase sequencing. Comparative 16S rDNA sequence analysis of V. spinosum with a group of environmental clones, considered to represent a novel phylum, reveals their relatedness, and allows assignment of these clones to a known main line of descent. This phylogenetic relationship is supported by the presence in the 16S rDNA sequence of V. spinosum of signature nucleotides previously considered unique for the environmental clone cluster.
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- Genome Analysis
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Determination of a 17484 bp nucleotide sequence around the 39° region of the Bacillus subtilis chromosome and similarity analysis of the products of putative ORFs
We have determined a 17484 bp nucleotide sequence around the 39° region, located about 480 kb downstream from the zero position of the Bacillus subtilis chromosome physical map. Among the 17 putative ORFs identified, orf1 and orf2 seem to correspond to mtlA and mtlB, encoding mannitol-specific phosphotransferase enzyme II and mannitol-1-phosphate dehydrogenase, respectively. orf4 seems to be another signal peptidase I gene (sipS) of B. subtilis. The putative products of six ORFs were similar to known proteins in data banks, namely a hypothetical 29-7 kDa protein of Escherichia col (Orf7), a lactam utilization protein (Orf8), the urea amidolyase of yeast (Orf12), the IcIR regulatory protein for aceAB of Salmonella typhimurium (Orf13), penicillin-binding protein 2 (Orf16) and aryl-alcohol dehydrogenase (Orf17). The amino acid sequence of Orf3 showed 34% identity with that of LeuC of B. subtilis, though they seem to be functionally different. The remaining seven ORFs did not show similarity to any known proteins.
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- Corrigendum
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- Indexes
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