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Frederic Barras Jean Pierre Chambost Marc Chippaux 《Molecular & general genetics : MGG》1984,197(3):486-490
Summary The study of mutants of Erwinia specifically unable to ferment cellobiose indicates that the mutations are clustered between arg and ile on the chromosome of this organism. In vivo cloning of the genes responsible for cellobiose utilization lead to a plasmid, pBEC2, which complements all Erwinia Clb- specific mutants. When introduced into wild-type E. coli it allows this organism to use cellobiose, arbutin and salicin; it also complements bglB and bglC mutants of Escherichia coli indicating that arbutin and salicin utilization is due to the products of the pBEC2 cloned genes. From the characterization of mutants pleiotropically affected in the utilization of various carbon sources, including cellobiose, arbutin and salicin, it is proposed that the three--glucosides are substrates of the phosphoenolpyruvate-dependent phosphotransferase system (PTS). 相似文献
56.
Stimulation of de novo synthesis of δ-aminolevulinate dehydralasc of radishes grown under far-red light .
Density labelling studies of δ-aminolevulinate dehydratase (ALAD) in cotyledons of radish ( Raphanus sativus L. cv. Longue Rave Saumonée) seedlings demonstrate that far-red light stimulates de novo synthesis of ALAD and that the turn-over of this enzyme is very poor. Cycloheximide reduces considerably both the increase of ALAD activity and the incorporation of deuterium in ALAD, which indicates that ALAD synthesis depends upon cytoplasmic ribosomes. 相似文献
Density labelling studies of δ-aminolevulinate dehydratase (ALAD) in cotyledons of radish ( Raphanus sativus L. cv. Longue Rave Saumonée) seedlings demonstrate that far-red light stimulates de novo synthesis of ALAD and that the turn-over of this enzyme is very poor. Cycloheximide reduces considerably both the increase of ALAD activity and the incorporation of deuterium in ALAD, which indicates that ALAD synthesis depends upon cytoplasmic ribosomes. 相似文献
57.
Pierre Lasserre Thierry Tournié 《Journal of experimental marine biology and ecology》1984,74(2):123-139
Metabolic processes occurring at the sea-water-sediment interface were studied using a circulation flow microcalorimeter. A methodology was developed to characterize rapid and global changes in metabolism and energy flow, not easily detectable with reductionist approaches. Sea water was pumped continuously, 5–10 mm above the sediment, in experimental microcosms; a 100-μm filter prevented passage of meiofauna. This “circulating interface” was taken through the microcalorimeter and from there to an oxygen electrode, and was returned to the microcosm. The microcosms were experimentally eutrophicated using peptone (4 mg·ml ?1). The relationship between heat production and oxygen tension in the circulating interface has been compared with ATP production, 14CO2 and [14C]particulate matter turnovers. Initial heat steady-state production rises to a peak of 130 to 180 μW·ml?1 in 6 to 8 h after peptone treatment. The microcalorimetric peak is closely correlated with 14CO2 turnover and partially correlated with micro-events on the pO2 curve. ATP concentration and particulate-14C turnover increase constantly and then stabilize, with the establishment of a new heat production steady state. The approach provides an indication of the temporal behaviour of complex mixtures of microorganisms and ciliates at the water-sediment interface, and gives holistic measurements of energy flow after induced perturbation (eutrophication) of the ecosystem. Although many problems remain to be solved in this field, it is shown here that flow microcalorimetric measurements can be used to monitor the effects of addition of reagents like pollutants and nutrients. 相似文献
58.
Several models have been proposed to interpret the mechanism of proton-pumping associated with the electron transfer reactions in the cytochrome b/f complex. Energetics considerations suggest that the proton pump is coupled to the oxidation of cytochrome b by plastoquinone. Experiments performed in living cells under anaerobic conditions suggest that proton-pumping can occur through two independent mechanisms. When the two b cytochromes are reduced prior to a flash illumination i.e. after a long dark anaerobic incubation (>10 minutes), proton-pumping is very likely associated with the reduction of a semiquinone by cyt b which occurs at a site close to the inner face of the membrane. The electrogenic phase is associated with the tranfer of protons via a transmembrane channel. This process is not inhibited by 2-n-nonyl-4-hydroxyquinoline N-oxide (NQNO). Under repetitive-flash or under aerobic conditions, proton-pumping occurs according to a modified Q-cycle mechanism, which is inhibited by NQNO.Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement 相似文献
59.
Neurofilament (NF) protein kinase, partially purified from NF preparations [Toru-Delbauffe & Pierre (1983) FEBS Lett. 162, 230-234], was found to be distinct from both the casein kinase present in NFs and the cyclic AMP-dependent protein kinase which is able to phosphorylate NFs. NF-kinase phosphorylated the three NF protein components. The amount of phosphate incorporated per molecule was higher for NF 200 than for NF 145 and NF 68. Other proteins present in the NF preparations were also used as NF-kinase substrates. Two of them might correspond to the myelin basic proteins with Mr values of 18,000 and 21,000. Four other substrates in the NF preparation were not identified (respective Mr values 53,000, 55,000, 65,000 and greater than 300,000). NF kinase also phosphorylated two additional brain-cell cytoskeletal elements: GFAp and vimentin. Casein, histones and phosvitin, currently used as substrates for protein kinase assays, were very poor phosphate acceptors. Half-maximal NF-kinase activity was obtained at an NF protein concentration of about 0.25 mg/ml in heated, salt-washed, NF preparations. The specific activity was about 5 pmol of 32P incorporated/min per microgram of NF kinase preparation protein. ATP was a phospho-group donor (Km 8 X 10(-5) M), but GTP was not. NF-kinase activity remained stable at 65 degrees C for more than 1 h. The enzyme was not degraded by storage at -20 degrees C for several months in a buffer containing 50% (w/v) sucrose. Maximal activity was obtained with 5 mM-Mg2+ (Mg2+ could be replaced by Co2+); Zn2+ and Cu2+ inhibited the reaction. NF-kinase was not dependent on cyclic AMP, cyclic GMP, Ca2+ or Ca2+ plus dioleoylglycerol and phosphatidylserine. 相似文献
60.
Cloning of Micrococcus luteus 3-methyladenine-DNA glycosylase genes in Escherichia coli 总被引:1,自引:0,他引:1
The 3-methyladenine-DNA glycosylase (m3ADG) excises 3-methyladenine (m3A) residues formed in DNA after treatment with alkylating agents. In Escherichia coli, the repair of this type of damage depends on the products of the genes tagA and/or alkA, which code for m3ADG I (20 kDa) and II (30 kDa), respectively. The tagA- and alkA--single mutants are sensitive to alkylating agents, the double mutant much more so. We have cloned two genes of Micrococcus luteus that can partly substitute the function of the E. coli tagA- and alkA- genes. An M. luteus genome bank was made by shotgun cloning of EcoRI + BamHI-digested DNA into pBR322. Two hybrid plasmids were identified that confer methylmethane sulfonate (MMS) resistance to the tagA- ada+ mutant and a capacity to reactivate MMS-treated bacteriophage lambda. Each hybrid plasmid directed the synthesis of 21-kDa m3ADG in E. coli tagA- ada-, which were not inhibited by 4 mM m3A. However, the restriction maps of the two cloned genes were different, and they showed no sequence homology as judged by the lack of cross hybridization. 相似文献