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111.
Michael P. Wilkie Chris M. Wood 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》1996,113(4):665-673
The Lake Magadi Tilapia (MT; Oreochromis alcalicus grahami, the Lahontan cutthroat trout (LCT; Oncorhynchus clarki henshawi) and the tarek (Ct; Chalcalburnus tarichi) have evolved unique strategies that allow them to overcome problems associated with ammonia excretion (JAmm) and acid-base regulation in their alkaline environments. In Lake Magadi, Kenya (pH 10), the MT circumvents problems associated with JAmm by excreting virtually all (>90%) of its waste-nitrogen as urea. Base excretion appears to be facilitated by modified seawater-type gill chloride cells, through apical Cl−/HCO3− exchangers and an outwardly directed OH−/HCO3−/CO3= excretion system. The LCT avoids potentially toxic increases in internal ammonia by permanently lowering ammonia production rates following transfer into alkaline (pH 9.4) Pyramid Lake, Nevada, from its juvenile freshwater (pH 8.4) environment. Greater apical exposure of LCT gill chloride cells, presumably the freshwater variety, probably facilitates base excretion by elevating Cl−/HCO3− exchange capacity. In Lake Van, Turkey (pH 9.8) high ammonia tolerance enables C. tarichi to withstand the high internal ammonia concentrations that it apparently requires for the facilitation of JAmm. It also excretes unusually high amounts of urea. We conclude that adjustments to nitrogenous waste metabolism and excretion patterns, as well as modifications to gill functional morphology, are necessary adaptations that permit these animals to thrive in environments considered unsuitable for most fishes. 相似文献
112.
R. O. D. Dixon 《Plant and Soil》1987,100(1-3):149-156
Summary The apparent Km(hydrogen) for uptake of hydrogen by pea root nodules was determined. This enabled the concentration gradient necessary for the evolution
of hydrogen to be calculated for nodules with no hydrogenase activity. This indicated that hydrogen inhibition of nitrogenase
is not likely to be the cause of the low relative efficiency of legume root nodules. The factors that affect electron allocation
between protons and nitrogen in nitrogenase are reviewed and it is concluded that there must be some as yet unknown factor
that affects electron distribution inRhizobium nitrogenase. One possibility is put forward and considered. A strain ofRhizobium was used that was found to possess hydrogenase activity in combination with pea variety Feltham First but not with variety
Meteor. The control of this enzyme is briefly discussed. 相似文献
113.
Urate was taken up at a negligible rate by Chlamydomonas reinhardtii cells grown on ammonium and transferred to media containing urate plus ammonium or urate plus chloral hydrate or cycloheximide. Addition of ammonium to cells actively consuming urate produced a rapid inhibition of urate uptake whereas the intracellular oxidation of urate was unaffected. Methylammonium but not glutamine or glutamate inhibited urate uptake. Addition of l-methionine-dl-sulfoximine to cells actively consuming urate provoked ammonium excretion, which was accompanied by a rapid inhibition of urate uptake. In cells growing on urate and exhibiting noticeable levels of nitrite-reductase activity, nitrite caused a sudden inhibition of urate uptake whereas nitrate required a time to induce nitrate reductase and to exert its inhibitory effect on uptake. The urate-uptake system did not require urate for induction since the urate-uptake capacity appeared in nitrogen-starved cells. From these results it is concluded that, in Chlamydomonas reinhardtii, ammonium inhibits urate uptake and also acts as co-repressor of the uptake system. 相似文献
114.
Summary Labelling experiments with15N glutamate and15N alanine were conducted using slices from oat leaves to investigate photorespiratory nitrogen metabolism. It is concluded from the labelling kinetics of glutamine that the refixation of photorespiratory ammonia primarily occurs by glutamine synthetase in the chloroplast. The labelling kinetics of glutamine with15N glutamate indicate that the chloroplastic and cytoplasmic glutamate pools do not exchange easily in oat leaf cells. Alanine was shown to be an important amino donor for photorespiratory glycine formation. This result is discussed with regard to a possible role of alanine in photorespiration. A modification to the scheme of photorespiratory nitrogen metabolism is proposed. 相似文献
115.
Ammonia reversibly inhibits the nitrogenase activity not only in purple nonsulfur bacteria but in purple (Thiocapsa roseopersicina) and green (Chlorobium limicola forma thiosulfatophilum) sulfur bacteria as well.The complete inhibition of nitrogenase activity (acetylene reduction) is observed about 30 s after addition of NH
4
+
(2.5×10-6 M) to cell suspensions. The pattern of ammonia inhibition of acetylene reduction in T. roseopersicina does not differ from the action of tetrabutylammonium and tetraphenylphosphonium (3 · 10-6-5·10-5 M) on nitrogenase activity of this bacterium.Simultaneously with the switch-off effect of NH
4
+
a considerable increase of ATP in cells of Rhodobacter sphaeroides and C. limicola f. thiosulphatophilum was observed. 相似文献
116.
本文测定了浑球红假单胞菌(Rhodobacter sphaeroides)菌株601谷氨酰胺合成酶(GS)、谷氨酸合酶(GOGAT)、谷氨酸脱氢酶(GDH)和丙氨酸脱氢酶(ADH)的活性。低氨时,GS/GOGAT活力高,GDH活力低,高氨时,GS/GOGAT活力低,GDH活力高。在以分子氮或低浓度氨为氮源的培养条件下,加入GS抑制刑MSX(L—methionine—DL—sulphoximine),细菌生长受到抑制。但是,生长在以谷氨酸为氮源的细菌则不受影响。上述结果表明,浑球红假单胞菌菌株601氨同化是通过GS/GOGAT途径和GDH途径。 相似文献
117.
Protective effect of L-carnitine on hyperammonemia 总被引:1,自引:0,他引:1
The diheme cytochrome c-554 which participates in ammonia oxidation in the chemoautotroph , Nitrosomonas europaea has been studied by Soret excitation resonance Raman spectroscopy. The Raman spectrum of reduced cytochrome c-554 at neutral pH is similar classical 6-coordinate low-spin ferrous mammalian cytochrome c. In contrast, the spectrum of ferric cytochrome c-554 suggests a 5-coordinate state which is unusual for c hemes. The oxidized spectrum closely resemble that of horseradish peroxidase (HRP) or cytochrome c peroxidase (CcP) at pH 6.4. The narrow linewidth of the heme core-size vibrations indicates that both heme irons of c-554 have similar geometries. 相似文献
118.
Carbon metabolism in photosynthesizing and respiring cells of Botryococcus braunii was radically changed by the presence of 1 mM NH4Cl in the medium, when the so-called resting state previously had been subjected to a nitrogen-deficient medium. Ammonia addition to the algae photosynthesizing with 14C-labelled HCO
3
-
almost completely inhibited the synthesis of 14C-labelled botryococcenes and other hexane-extractable compounds, and also inhibited the formation of insoluble compounds; however, it resulted in a large increase in the synthesis of alanine, glutamine, other amino acids, and especially of 5-aminolevulinic acid. Total CO2 fixation decreased about 60% and O2 evolution decreased more than 50%.CO2 fixation in the dark with ammonia present led to labelled products derived from phosphoenolpyruvate carboxylation, such as glutamine, glutamate, and malate. Respiratory uptake of O2 increased by about 70%.The inhibition of terpenoid synthesis and increased synthesis of C5 amino acids by Botryococcus upon ammonia addition indicates 1) a diversion of acetyl coenzyme A from synthetic pathways leading to terpenoids and 2) increased operation of pathways leading to the synthesis of amino acids, especially 5-aminolevulinic acid, a precursor to chlorophyll biosynthesis.This work was supported in part by the Office of Energy Research, Office of Basic Energy Sciences, Biological Energy Research Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098, in part by a grant from SOHIO, and, in part, by a grant from the Japan-U.S. Cooperative Science Program (The Japan Society for the Promotion of Science, National Science Foundation, Division of International Programs) 相似文献
119.
J. Taneja P. M. Guerin 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,181(1):21-34
1) Nymphs of the haematophagous bug Triatoma infestans (Heteroptera: Reduviidae) are attracted to volatiles from their own faeces on a servosphere. 2) Biological substrates attractive
to triatomines release NH3: wetted triatomine faecal papers release NH3 at 256 ppb NH3 from a 60-g source and stale rabbit urine at 394 ppb from 200 ml. Ammonia released from aqueous NH3 also attracts bugs at doses of 3 ppb and 17 ppb on the servosphere. 3) Bugs typically show negative anemotaxis in a stimulus-free
air-stream on the servosphere. At onset of stimulation with ammonia from either biological substrates or aqueous NH3 the bugs stop, move their antennae, turn and walk upwind, i.e. odour-mediated anemotaxis. 4) At lower NH3 doses a latency in attraction is recorded, but this latency disappears when the relative humidity of the stimulus delivery
air-stream is dropped from 90 to 35%. 5) Electrophysiological recordings from single olfactory sensilla on antennae of Triatoma nymphs reveal two different types of NH3-excited receptors, both within grooved-peg sensilla. The responses of one of these receptor cells to NH3 has been studied in detail and shows that the action potential discharge rate is dose-dependent over the range 2–200 ppb.
6) The amplitudes of electroantennograms recorded from Triatoma nymphs to NH3 are dose dependent over the range 5–550 ppb.
Accepted: 16 January 1997 相似文献
120.
Dalene Vosloo Andre VoslooElisabeth J. Morillion Jessika N. SamuelsPaula Sommer 《Journal of thermal biology》2013
When ectotherms are exposed to high temperatures, cellular oxygen demand increases. When oxygen demand exceeds oxygen availability, animals may experience functional hypoxia regardless of environmental oxygen levels. 相似文献