Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cultures of Streptomyces venezuelae grown in a medium containing glucose with mixtures of ammonium and nitrate as the nitrogen source produced chloramphenicol in a distinct idiophase that followed biomass accumulation. Analysis of fermentation broths showed that ammonium and nitrate were taken up consecutively by the organism. Measurements of nitrate reductase in the mycelium established that the enzyme was constitutive and that its specific activity did not increase during the period when ammonium was exhausted from the medium and nitrate was assimilated. The enzyme was neither repressed nor inhibited by ammonium. Production of chloramphenicol was also delayed until ammonium had been consumed and remained slow until subsequent depletion of nitrate. Arylamine synthetase, the initial enzyme in the pathway of antibiotic biosynthesis, showed no marked change in specific activity during utilization of the two nitrogen sources. The result suggests that the mechanism causing preferential utilization of ammonium does not simultaneously control the onset of chloramphenicol biosynthesis.
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PMID:Suppression of nitrate utilization by ammonium and its relationship to chloramphenicol production in Streptomyces venezuelae. 648 3

The development of castor bean (Ricinus communis L. var. sanguineus) leaves from bud break to abscission was studied to determine whether senescence of phloem precedes or follows chlorophyll degradation in the course of natural ageing of leaves. The castor bean leaf blade took 20 days for full expansion and its average life span was 60 days. From the day of full expansion on it suffered a substantial loss in N, a small loss in C, K and P and a gain in Ca, Mg and S. The content of soluble sugars increased with time, paralleled by a decrease of photosynthetic activity. Starch accumulated shortly before chlorophyll breakdown. The amino acid level in the leaves decreased steadily together with nitrate reductase and glutamine synthetase activity. Reactive oxygen species increased and oxidation-protecting compounds decreased during the life span of the leaves. Shortly after full leaf expansion an increasing number of sieve plates showed strong callose depositions when visualized by aniline blue method. At day 40 only half of the sieve tubes appeared functional. Chlorophyll breakdown followed these processes with a time lag of approximately 10 days. The sieve tube sap of ageing leaves had the same sucrose concentrations as young leaves, whereas amino acid concentrations decreased. High levels of reduced ascorbic acid and glutathione together with increasing levels of glutaredoxin indicated oxidative strain during senescence. We speculate that the gradual increase of reactive oxygen species during ageing together with the import of calcium ions lead to the stimulation of callose synthesis in plasmodesmata and sieve plates with the consequence of inhibition of phloem transport leading to carbohydrate back-up in the leaf blade. The latter may finally induce chlorophyll breakdown and, at the end, leaf abscission at the petiole base. Thus phloem blockage would precede and may be causal for chlorophyll degradation in leaf senescence.
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PMID:Sequence of morphological and physiological events during natural ageing and senescence of a castor bean leaf: sieve tube occlusion and carbohydrate back-up precede chlorophyll degradation. 1503 69

Monolayers of Cu(II)-complexes on electrode surfaces are frequently applied for the immobilization and controlled orientation of His-tagged redox proteins. However, affinity binding is limited to applications that require potentials less negative than the reduction potential of the metal complexes. In order to overcome this limitation, we used Zn(2+) cations on nitrilotriacetic acid (NTA) modified carbon electrodes for the coordination of His-tagged nitrate reductase (NaR). The NTA modified electrodes were prepared upon diazotation and electrochemical reduction of an aniline functionalized NTA ligand. After coordination of Zn(2+) to the bound NTA ligand, self-assembly of NaR is achieved via coordination of the imidazole groups from the His-tag to the NTA-Zn(II) complex. The electrochemical investigations of the NaR monolayer on NTA-Zn(II) films demonstrate the catalytic activity for reduction of nitrate to nitrite in the presence of methyl viologen. The catalytic current density correlates with the one expected for a fully active enzyme monolayer. Moreover, the reduction of Zn(2+) is not observed at the potential necessary for the reduction of methyl viologen. Therefore, affinity binding based on Zn(2+) may be used for the immobilization and electrochemical applications of His-tagged NaR.
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PMID:Affinity binding via zinc(II) for controlled orientation and electrochemistry of histidine-tagged nitrate reductase in self-assembled monolayers. 2289 13