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

The effect of 0.5 millimolar O-acetyl-l-serine added to the nutrient solution on sulfate assimilation of Lemna minor L., cultivated in the light or in the dark, or transferred from light to the dark, was examined. During 24 hours after transfer from light to the dark the extractable activity of adenosine 5'-phosphosulfate sulfotransferase, a key enzyme of sulfate assimilation, decreased to 10% of the light control. Nitrate reductase (EC 1.7.7.1.) activity, measured for comparison, decreased to 40%. Adenosine 5'-triphosphate (ATP) sulfurylase (EC 2.7.7.4.) and O-acetyl-l-serine sulfhydrylase (EC 4.2.99.8.) activities were not affected by the transfer. When O-acetyl-l-serine was added to the nutrient solution at the time of transfer to the dark, adenosine 5'-phosphosulfate sulfotransferase activity was still at 50% of the light control after 24 hours, ATP sulfurylase and O-acetyl-l-serine sulfhydrylase activity were again not affected, and nitrate reductase activity decreased as before. Addition of O-acetyl-l-serine at the time of the transfer caused a 100% increase in acid-soluble SH compounds after 24 hours in the dark. In continuous light the corresponding increase was 200%. During 24 hours after transfer to the dark the assimilation of (35)SO(4) (2-) into organic compounds decreased by 80% without O-acetyl-l-serine but was comparable to light controls in its presence. The addition of O-acetyl-l-serine to Lemna minor precultivated in the dark for 24 hours induced an increase in adenosine 5'-phosphosulfate sulfotransferase activity so that a constant level of 50% of the light control was reached after an additional 9 hours. Cycloheximide as well as 6-methyl-purine inhibited this effect. In the same type of experiment O-acetyl-l-serine induced a 100-fold increase in the incorporation of label from (35)SO(4) (2-) into cysteine after additional 24 hours in the dark. Taken together, these results show that exogenous O-acetyl-l-serine has a regulatory effect on assimilatory sulfate reduction of L. minor in light and darkness. They are in agreement with the idea that this compound is a limiting factor for sulfate assimilation and seem to be in contrast to the proposed strict light control of sulfate assimilation.
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PMID:Regulation of Sulfate Assimilation by Light and O-Acetyl-l-Serine in Lemna minor L. 1666 78

A spontaneous mutant of Rhodobacter sphaeroides f. sp. denitrificans IL-106 was found to excrete a large amount of a red compound identified as coproporphyrin III, an intermediate in bacteriochlorophyll and heme synthesis. The mutant, named PORF, is able to grow under phototrophic conditions but has low levels of intracellular cysteine and glutathione and overexpresses the cysteine synthase CysK. The expression of molybdoenzymes such as dimethyl sulfoxide (DMSO) and nitrate reductases is also affected under certain growth conditions. Excretion of coproporphyrin and overexpression of CysK are not directly related but were both found to be consequences of a diminished synthesis of the key metabolite S-adenosylmethionine (SAM). The wild-type phenotype is restored when the gene metK encoding SAM synthetase is supplied in trans. The metK gene in the mutant strain has a mutation leading to a single amino acid change (H145Y) in the encoded protein. This point mutation is responsible for a 70% decrease in intracellular SAM content which probably affects the activities of numerous SAM-dependent enzymes such as coproporphyrinogen oxidase (HemN); uroporphyrinogen III methyltransferase (CobA), which is involved in siroheme synthesis; and molybdenum cofactor biosynthesis protein A (MoaA). We propose a model showing that the attenuation of the activities of SAM-dependent enzymes in the mutant could be responsible for the coproporphyrin excretion, the low cysteine and glutathione contents, and the decrease in DMSO and nitrate reductase activities.
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PMID:Coproporphyrin excretion and low thiol levels caused by point mutation in the Rhodobacter sphaeroides S-adenosylmethionine synthetase gene. 2003 86

Salinity is one of the abiotic factors that most affect crop growth and production. This study focused on the effect of high salinity on the endogenous levels of the signaling molecules hydrogen sulfite (H2S) and nitric oxide (NO) in Nicotiana tabacum leaves and the extent of these for the biochemically-driven plant tolerance to such abiotic stress. The NaCl treatment for 10days led to an expressive augment of H2S and NO levels. This increase was correlated with the raise of l-Cys and l-Arg and the induction of l-cysteine desulfhydrase, cyanoalanine synthase, cysteine synthase, nitrate reductase and arginase, enzymes known to be involved in the biosynthesis of H2S or NO. The enzymatic antioxidant system (superoxide dismutase and catalase activity) was boosted and the non-enzymatic antioxidant glutathione was intensively oxidized in leaves upon stress allowing plants to cope with oxidative stress. Lower stomatal conductance was observed in stressed plants in comparison with control ones. Moreover, the high activity of antioxidant enzymes and high rate of glutathione oxidation following salt stress were considerably decreased upon NO or H2S scavenging. Thus, increment in NO and H2S levels and their interplay, along with metabolic and physiological changes, contributed to tobacco survival to extreme salinity conditions.
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PMID:Salinity-induced accumulation of endogenous H2S and NO is associated with modulation of the antioxidant and redox defense systems in Nicotiana tabacum L. cv. Havana. 2816 28