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31.
Extracts of denitrifying bacteria grown anaerobically with phenol and nitrate catalyzed an isotope exchange between 14CO2 and the carboxyl group of 4-hydroxybenzoate. This exchange reaction is ascribed to a novel enzyme, phenol carboxylase, initiating the anaerobic degradation of phenol by para-carboxylation to 4-hydroxybenzoate. Some properties of this enzyme were determined by studying the isotope exchange reaction. Phenol carboxylase was rapidly inactivated by oxygen; strictly anoxic conditions were essential for preserving enzyme activity. The exchange reaction specifically was catalyzed with 4-hydroxybenzoate but not with other aromatic acids. Only the carboxyl group was exchanged; [U-14C]phenol was not exchanged with the aromatic ring of 4-hydroxybenzoate. Exchange activity depended on Mn2+ and inorganic phosphate and was not inhibited by avidin. Ortho-phosphate could not be substituted by organic phosphates nor by inorganic anions; arsenate had no effect. The pH optimum was between pH 6.5–7.0. The specific activity was 100 nmol 14CO2 exchange · min-1 · mg-1 protein. Phenol grown cells contained 4-hydroxybenzoyl CoA synthetase activity (40 nmol · min-1 · mg-1 protein). The possible role of phenol carboxylase and 4-hydroxybenzoyl CoA synthetase in anaerobic phenol metabolism is discussed. 相似文献
32.
Microbial desulfurization of coal by pyrite oxidizing bacterial enrichment cultures has been studied in air-agitated slurry reactors of 4- and 20-L volumes. Batch experiments showed that inoculation with an active bacterial culture is essential to minimize the lag phase, although a considerable number of pyrite oxidizing bacteria was found on the coal prior to desulfurization. For detailed investigations of kinetics, energy requirements, and technical applicability, a bioreactor equipment consisting of a cascade of eight stages was developed and operated continuously. Microbial desulfurization of coal-monitored by measuring the axial profile of dissolved iron concentration, real and maximum oxygen consumption rates, and cell concentration-at pulp densities to 30% was performed over a period of 200 days without any disturbances concerning the aeration system, fluidization, transport of solids and microbial growth. At a pulp density of 20%, a pyrite conversion of 68% was achieved after the third reactor stage at a total residence time of five days in the first three stages. The kinetics of pyrite degradation were found to be well described by a rate equation of first order in pyrite surface area concentration if the pyrite is directly accessible for microbial attack. Rate constants were determined to 0.48 mg pyrite/(cm(2) day) in the first and to 0.24 mg pyrite/(cm(2) day) in the following reactor stages. Kinetic models taking into account adsorption/desorption as well as growth kinetics failed to describe the observed reaction rates. However, a model treating pyrite degradation and microbial growth kinetics formalistically seems to be applicable when backmixing between the reactor stages can be avoided. The advantage of a multistage reactor in comparison to single-stage equipment was shown by calculation. To obtain a pyrite conversion of 68%, a three-stage reactor would require only 58% of the volume of single-stage equipment.Measurement of oxygen consumption rates proved to provide quickly and easily measurable parameters to observe microbial coal desulfurization in technical scale: the real oxygen consumption rate is correlated to the pyrite oxidation rate and the maximum oxygen consumption rate is correlated to the concentration of viable cells. The Y(o/s) coefficient for the amount of oxygen consumed per mass unit of pyrite oxygen was determined to approximately 0.33 in comparison to 1.0 which can be calculated from stoichiornetry. This could yet not be explained. Chemical leaching experiments as well as sulfur analyses of desulfurized coal samples showed that the microorganisms play the main role in degradation of pyrite from coal and that pyrite oxidation by ferric iron can be neglected. 相似文献
33.
Site-specific mutants of human Cu,Zn superoxide dismutase (Cu,ZnSOD) have been prepared in which the active-site arginine at position 143 (i.e., SODR143) has been replaced by either lysine (SODK143) or isoleucine (SODI143). As reported previously (W.F. Beyer, Jr., et al. (1987) J. Biol. Chem. 262, 11182-11187), SODK143 and SODI143 have 43 and 11%, respectively, of the catalytic activity of SODR143. H2O2, at low concentrations, acts as an affinity reagent for the inactivation of SODR143. At pH 9.0 and 25 degrees C, the process is characterized by a half-saturation constant for H2O2, K50, of 5.1 mM and a maximum pseudo-first-order rate constant for inactivation, Kmax, of 0.53 min-1. At pH 11.5, the corresponding values are 0.63 mM and 1.23 min-1. The active species in the inactivation is likely HO2-, as previously found with yeast and bovine Cu,ZnSODs (see C.L. Borders, Jr., and I. Fridovich (1985) Arch. Biochem. Biophys. 241, 472-476). SODK143 is also inactivated by HO2- by an affinity mechanism, i.e., one where reversible binding of H2O2 (HO2-) is a prerequisite for inactivation. At pH values of 9.0 and 11.5, the kmax values are 0.92 and 1.08 min-1, respectively; however, the corresponding K50 values increase to 42.5 and 15.8 mM, respectively. SODI143 is also inactivated by H2O2, but no evidence for an affinity mechanism was found; instead, a second-order kinetic mechanism was observed. Inactivation of each of the three enzymes is accompanied by the loss of one histidine per subunit. At elevated concentrations of H2O2, a second nonaffinity mechanism of inactivation of both SODR143 and SODK143 was found, in which a second equivalent of H2O2 reacts with the Cu,ZnSOD.HO2- complex to give a competing second-order inactivation. It appears that the positive charge of arginine-143 plays a role in the binding of HO2- at the active site of human Cu,ZnSOD, and that replacement of the arginine by lysine gives an enzyme with a similar affinity mechanism of inactivation, but with a greatly reduced affinity for HO2-. However, replacement with isoleucine causes an entirely different mechanism of inactivation; this raises the possibility that the mechanism of enzyme catalysis of superoxide dismutation by SODI143 is also different. 相似文献
34.
Bruno Schwarzkopf Brigitte Reuke Andreas Kiener Adelbert Bacher 《Archives of microbiology》1990,153(3):259-263
Growing cultures of Methanobacterium thermoautotrophicum were supplemented with [U-14C]adenosine or [1-14C]adenosine. 7,8-Didemethyl-8-hydroxy-5-deazariboflavin (factor F0) and 7-methylpterin were isolated from the culture medium. Hydrolysis of cellular RNA yielded purine and pyrimidine nucleotides. The ribose side chain of proffered adenosine is efficiently incorporated into cellular adenosine and guanosine nucleotide pools but not into pyrimidine nucleotides. Thus, M. thermoautotrophicum can utilize exogenous adenosine by direct phosphorylation without hydrolysis of the glycosidic bond, and AMP can be efficiently converted to GMP. Factor F0 and 7-methylpterin had approximately the same specific activities as the purine nucleotides. It follows that the ribityl side chain of factor F0 is derived from the ribose side chain of a nucleotide precursor by reduction. The pyrazine ring of methanopterin is formed by ring expansion involving the ribose side chain of the precursor, GTP.Abbreviations Factor F0
8-hydroxy-6,7-didemethyl-5-deazariboflavin
- APRT
adenine phosphoribosyltransferase
- GPRT
guanine phosphoribosyltransferase
- PRPP
phosphoribosylpyrophosphate
- HPLC
high performance liquid chromatography 相似文献
35.
36.
Andreas Kiener William H. Orme-Johnson Christopher T. Walsh 《Archives of microbiology》1988,150(3):249-253
Intracellular levels of F390 (AMP and GMP adducts of the 5-deazaflavin cofactor F420) in Methanobacterium thermoautotrophicum were analysed after gasing fermenter cultures with several consecutive cycles of substrate gas and gas mixtures containing 5% oxygen. No F390 was detected in growing cells, hydrogen starved cells and CO2 starved cells prior to O2 contamination. Also, no F390 was found in hydrogen depleted cells after O2 treatment. Exposure of exponentially growing cells and CO2 starved cells to oxygen lead to the formation of F390 species; the increase in the detected amount of F390 was coupled to a decrease of the F420 level. As soon as anaerobiosis was reestablished F390 cofactors were degraded and growth proceeded. Independent of the physiological condition of Methanobacterium thermoautotrophicum methanopterin was formed upon O2 exposure. After normal growth conditions were restored the level of detected methanopterin decreased again. 相似文献
37.
Dr. Wolfgang Schwabe Andreas Weihe Thomas Börner Manfred Henning Johannes-Günther Kohl 《Current microbiology》1988,17(3):133-137
The plasmid content and toxicity of nine different strains ofMicrocystis aeruginosa have been analyzed. The two toxic strains of the HUB Culture Collection were found to carry each two plasmids, pMA1 and pMA2, of 2.9 kb and 8.5 kb, respectively. In strains PCC 7813 and PCC 7820, also toxic, two different plasmids of 2.6 kb and 16 kb were detected. Hybridization experiments showed that there exists no sequence homology between the pMA plasmids and the plasmids found in the PCC strains; but the pMA plasmids hybridized to chromosomal DNA of the toxic strains PCC 7820, PCC 7813, HUB 063, and the nontoxic strain HUB 5-3. In nontoxic strains no or at most one plasmid of unstable occurrence could be detected. Only one of the toxic strains investigated, SAG 14.85 (NRC-1), contained no plasmid. 相似文献
38.
Bernhard Ronacher Andreas Stumpner 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1988,163(4):517-523
Summary In females of the acridid grasshopperChorthippus biguttulus, thoracic auditory interneurons were investigated with respect to their selectivity for temporal parameters of the conspecific song. Special attention was given to the detection of small gaps in the syllables of the song, since behavioural experiments have shown that the presence or absence of gaps is critical for the female's Innate Releasing Mechanism (cf. Fig. 1).The spiking response of one ascending interneuron, the AN4, shows filtering properties which closely resemble the behavioural reactions (cf. Figs. 1, 3 and 5b). The difference in the AN4's reaction to stimuli with gaps and uninterrupted stimuli is maintained over the behaviourally relevant intensity range (Fig. 4). This reaction is reliable enough that the stimulus type could be inferred by higher centres even from single stimulus presentations. Hence, this neuron is likely to participate in the task of gap detection and probably is a part of the neuronal filter network which determines the characteristics of the Innate Releasing Mechanism of this species. However, this interneuron is not species-specific: A homologue exists in other acridids as well and, inLocusta migratoria, has similar response characteristics (Fig. 6). The inferences of this observation for the evolution of an Innate Releasing Mechanism are discussed.Abbreviations
CNS
central nervous system
-
PST-histogram
post-stimulus-time-histogram
-
SPL
sound pressure level
-
IRM
Innate Releasing Mechanism 相似文献
39.
40.
In isolated papillary muscles of guinea-pig hearts, the inotropic effects of bivalent cations, Ca2+, Ba2+, Sr2+, and Ni2+, were investigated during post-rest adaptation in order to study their individual action on excitation-contraction coupling. Upon exposure to each cation studied, the force of contraction was transiently enhanced, whereas the steady state force was influenced differently: it increased with Ca2+, Ba2+ and Sr2+ and was depressed by Ni2+. The transmembrane action potentials (measured at 90% repolarization) were slightly prolonged by Sr2+ and even more by Ba2+, and were shortened by Ca2+ and Ni2+. After 10 min rest, the post-rest contractions consisted of a late peak (PII) that was enhanced in high Ca2+-solution an by Sr2+. Ni2+ and Ba2+ depressed PII and during adaptation to pre-rest controls an early peak of contraction (PI) prevailed. There was no simple relation between post-rest adaptation of force and the duration of action potential in the presence of the bivalent cations tested. During post-rest adaptation the two components of contraction can be separated. The results are interpreted in terms of a model of excitation-contraction coupling which derives Ca ions for contractile activation from two sources: transmembrane calcium influx and calcium release from cellular stores. From the different effects on post-rest adaptation it is concluded that the individual cations influence excitation-contraction coupling more specifically and not merely by "screening-off" the negative surface charges. 相似文献