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)

A positive, genetic selection against the activity of the nitrogen regulatory (NTR) system was used to isolate insertion mutations affecting nitrogen regulation in Klebsiella aerogenes. Two classes of mutation were obtained: those affecting the NTR system itself and leading to the loss of almost all nitrogen regulation, and those affecting the nac locus and leading to a loss of nitrogen regulation of a family of nitrogen-regulated enzymes. The set of these nac-dependent enzymes included histidase, glutamate dehydrogenase, glutamate synthase, proline oxidase, and urease. The enzymes shown to be nac independent included glutamine synthetase, asparaginase, tryptophan permease, nitrate reductase, the product of the nifLA operon, and perhaps nitrite reductase. The expression of the nac gene was itself highly nitrogen regulated, and this regulation was mediated by the NTR system. The loss of nitrogen regulation was found in each of the four insertion mutants studied, showing that loss of nitrogen regulation resulted from the absence of nac function rather than from an altered form of the nac gene product. Thus we propose two classes of nitrogen-regulated operons: in class I, the NTR system directly activates expression of the operon; in class II, the NTR system activates nac expression and the product(s) of the nac locus activates expression of the operon.
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PMID:Role of the nac gene product in the nitrogen regulation of some NTR-regulated operons of Klebsiella aerogenes. 197 23

Glutamine synthetase activity in the ascomycete fungus Aspergillus nidulans is regulated by nitrogen source. The lowest activities are obtained when the fungus is grown on L-glutamine, and the highest activities when grown on L-glutamate + arabinose. Glutamine auxotrophs of the fungus have been isolated, and one of these mutant strains, glnA-1, has been shown to lack the enzyme glutamine synthetase. The mutation is recessive, and is located on the right arm of chromosome II. In addition to abolishing glutamine synthetase activity, the mutation results in the relief of repression for several enzyme activities normally subject to repression by ammonium. These include nitrate reductase, asparaginase, proline uptake and urea uptake.
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PMID:A single mutation leads to loss of glutamine synthetase and relief of ammonium repression in Aspergillus. 2418 46