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)

The tehAtehB operon from the Escherichia coli chromosome (32.3 min) mediates resistance to potassium tellurite (K2TeO3) when expressed on a multicopy plasmid such as pUC8 (pTWT100). An MIC of 128 micrograms ml-1 is observed when tehAtehB is expressed in a wild-type host and grown on rich media. In this study, the tehAtehB determinant was transformed into mutants deficient in electron transport processes and/or thiol redox coupling within E. coli. These mutants included ubi, nad, cys, nar, trx, grx, gsh and sod. MICs of tehAtehB transformed into these mutants ranged from 1-16 micrograms K2TeO3 ml-1 compared to 0.03-2 micrograms ml-1 for strains transformed with a control plasmid. The tellurite-resistance determinant locus kilA cloned from the IncP alpha plasmid RK2Ter (pDT1558) was also investigated in these strains. This tellurite-resistance determinant showed little or no dependency on the host genotype. The ability of tehAtehB to mediate resistance in wild-type hosts is limited to rich medium. Rich medium may provide a key unidentified cofactor required by TehATehB that is not provided under minimal conditions. Again, the ability of the kilA determinant to mediate tellurite resistance was independent of medium conditions. These data suggest that either a reducing environment or electron-reducing equivalents are required for tehAtehB to mediate high levels of resistance to potassium tellurite. Therefore, the two resistance determinants studied here possess two very different biochemical mechanisms of resistance. Our data also suggest a mechanism for endogenous resistance to tellurite which involves nitrate reductase, superoxide dismutase, and thiol redox processes.
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PMID:The tellurite-resistance determinants tehAtehB and klaAklaBtelB have different biochemical requirements. 857 7

A unique class of chlorate-resistant mutants of Escherichia coli which produced formate hydrogenlyase and nitrate reductase activities only when grown in medium with limiting amounts of sulfur compounds was isolated. These mutants failed to produce the two molybdoenzyme activities when cultured in rich medium or glucose-minimal medium. The mutations in these mutants were localized in the moeA gene. Mutant strains with polar mutations in moeA which are also moeB did not produce active molybdoenzymes in any of the media tested. moeA mutants with a second mutation in either cysDNCJI or cysH gene lost the ability to produce active molybdoenzyme even when grown in medium limiting in sulfur compounds. The CysDNCJIH proteins along with CysG catalyze the conversion of sulfate to sulfide. Addition of sulfide to the growth medium of moeA cys double mutants suppressed the MoeA- phenotype. These results suggest that in the absence of MoeA protein, the sulfide produced by the sulfate activation/reduction pathway combines with molybdate in the production of activated molybdenum. Since hydrogen sulfide is known to interact with molybdate in the production of thiomolybdate, it is possible that the MoeA-catalyzed activated molybdenum is a form of thiomolybdenum species which is used in the synthesis of molybdenum cofactor from Mo-free molybdopterin.
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PMID:Physiological and genetic analyses leading to identification of a biochemical role for the moeA (molybdate metabolism) gene product in Escherichia coli. 951 15

In Neurospora crassa, the nit-3 gene, which encodes nitrate reductase, an enzyme required for the utilization of inorganic nitrate, is subject to a high degree of genetic and metabolic regulation as a member of the nitrogen control circuit. The nit-3 gene promoter contains binding sites for a globally acting protein NIT2 and a pathway-specific protein NIT4. Expression of the nit-3 gene absolutely requires both the NIT2 and NIT4 transcription factors and only occurs under conditions of nitrogen source derepression and nitrate induction. In the sulfur control circuit, the cys-14 gene encodes sulfate permease II, which facilitates the assimilation of sulfate. Expression of cys-14 is strongly regulated by only a single positive-acting factor, CYS3. It was of interest to determine whether NIT2 or NIT4 alone was capable of turning on the expression of cys-14, since this structural gene is normally controlled by only one regulatory protein. NIT2- and/or NIT4-binding elements were introduced into the promoter of a wild-type cys-14 gene and these constructs were transformed into a cys-13(-) cys-14(-) mutant strain and into a nit-2(-) mutant host. We examined whether any of these cys-14 genes in these transformants could now be controlled as a nitrogen-regulated gene. Sulfate permease assays revealed that both NIT2 and NIT4 were required for cys-14 expression upon nitrate induction, while neither alone activated any detectable cys-14 expression. We thus conclude that neither NIT2 nor NIT4 is capable alone of activating gene expression in this context, but together they can cooperate to elicit strong activation.
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PMID:Cooperative action of the NIT2 and NIT4 transcription factors upon gene expression in Neurospora crassa. 1258 65