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)

Previous work (Rand and Arst, 1977) led to the proposal that the nis-5 mutation results in a new low activity promoter for niiA, the structural gene for nitrite reductase in Aspergillus nidulans. Expression of niiA via this promoter differs from expression of niiA via its normal promoter/initiator in that expression by the new promoter is not subject to nitrate induction or ammonium repression. nis-5 reduces but does not abolish niiA expression mediated by the normal promoter/initiator. In this work we show that nis-5 is associated with and is probably identical to a non-reciprocal translocation in which a considerable portion of the centromere proximal region of the right arm of linkage group II is inserted into linkage group VIII between niiA and niaD, the tightly linked, probably contiguous structural genes for nitrate reductase. This implies that niiA, along with its normal promots yet unidentified by its normal role. Further, it indicates that niiA is transcribed from the niaD-proximal side. As niiA and niaD are separated by a large number of unrelated genes in nis-5 strains, we can safely conclude that expression of niiA does not occur solely by synthesis of a messenger which carries a niaD as well as a niiA transcript. Clearly, niiA and niaD do not form an operon for which a di- (or poly-) cistronic messenger by the only transcript. This is consistent with other experimental evidence which shows that the syntheses of nitrate and nitrite reductases are not coordinately regulated. Nevertheless, all of these data would also be consistent with a model in which niiA and niaD form an operon-type structure having overlapping transcripts, one being di- (or poly-) cistronic and including both niiA and niaD and another being monocistronic for niiA. The reduced niiA expression mediated by the normal promoter/initiator in nis-5 strains could be a consequence of the functioning or positioning of the new linkage group II niiA promoter. An alternative, but not mutually exclusive, explanation would be that the insertional translocation prevents synthesis of a niiA niaD dicistronic transcript so that only that component of niiA expression which is due to a monocistronic niiA messenger can be induced by nitrate (and nitrite) in nis-5 strains. The apparently low activity of the new linkage group II promoter in comparison to the normal niiA promoter/initiator might betoken considerable efficiency of the latter rather than any particular lack of efficiency of the former. In addition, this work has involved extensive new mapping in linkage group II, including both mitotic mapping of the centromere and meiotic mapping of previously unlocated markers. A series of crosses in cluding genotype combinations both heterozygous and homozygous for nis-5 has been used to map the break-points and orientation of the translocation. As one break-point is closer to the centromere of linkage group II than the most centromere proximal identified gene on the same (i.e...
 ...
PMID:Do the tightly linked structural genes for nitrate and nitrite reductases in Aspergillus nidulans form an operon? Evidence from an insertional translocation which separates them. 38 64

We have used the penicillin selection method of Autissier & Kepes [(1972) Biochimie 54, 93--101] to study the segregation of membrane-bound respiratory nitrate reductase (EC 1.9.6.1) in Escherichia coli for the three generations after cessation of nitrate reductase synthesis caused by withdrawal of nitrate from the growth medium. We also included a physical separation procedure that permitted direct assay for nitrate reductase activity among all fractions produced by the penicillin selection method. We conclude that the segregation of nitrate reductase after cell division is dispersive, and not semi-conservative as proposed by Autissier & Kepes (1972).
 ...
PMID:Synthesis of cytoplasmic membrane during growth and division of Escherichia coli. Dispersive behaviour of respiratory nitrate reductase. 39 53

The maize root has two main proteinase and carboxypeptidase components. Proteinase I and carboxypeptidase I, which predominate in older plants, appear to have a serine group at their active sites and have been estimated to have molecular weights of approximately 54000 and 77000 respectively. Proteinase I, which has been purified up to 500-fold, degrades haemoglobin and azocasein with maximum activity at pH 4 and 9--10 respectively, while on maize root protein it gives most hydrolysis in the neutral pH range. The main portion of the nitrate-reductase-inactivating activity in the maize root extract is due to proteinase I. Carboxypeptidase I, like several other plant carboxypeptidases such as carboxypeptidase C which have now (IUB Recommendations 1978) been classified as serine carboxypeptidases (EC 3.4.16.1), has maximum activity around pH 5 and has esterase activity. A second group of proteases, proteinase II and carboxypeptidase II, separated from the above on carboxymethyl-cellulose, were shown to have different molecular weight properties and be equally sensitive to serine and thiol group inhibitors. Proteinase II degrades haemoglobin, but not azocasein and does not mediate nitrate reductase inactivation. Associated with this second group of proteases was a macromolecular component which inactivated nitrate reductase but, unlike the action of proteinase I, was not inhibited by phenylmethylsulphonyl fluoride or casein. It was inhibited by metal chelating agents which were without effect on nitrate reductase inactivation due to proteinase I.
 ...
PMID:Isolation and characterisation of peptide hydrolases from the maize root. 39 8

We have designed a new medium for the differentiation of mutants of Salmonella typhimurium defective in the ability to reduce nitrate with formate, and have characterized 24 formate dehydrogenase (FDH) mutants isolated on this medium. The mutants were assayed for the ability to use formate to reduce benzyl viologen and phenazine methosulfate, and were mapped by means of conjugation and P22-mediated transduction. Mutants lacking the ability to reduce either dye were found to map at three distinct sites: at a site co-transducible with xyl (presumably fdhA), at a site or sites between 13U and 33U, but not co-transducible with aroA, bio, purB, pyrC, or pyrD (near, but not identical with fdhB), and at asite 10-20% co-transducible with pyrE, for which we suggest the designation fdhC. Six mutant isolates reduced benzyl viologen, but not phenazine methosulfate. They retained the ability to produce nitrite during growth with nitrate. They mapped between 83U and 89U, but no co-transduction was found with metE, glnA, metB, or argH. The combined biochemical and genetic data suggest the existence of a gene in this area which is essential for the reduction of nitrate with formate, but not for formate hydrogenlyase activity or for nitrate reductase activity.
 ...
PMID:Formate dehydrogenase mutants of Salmonella typhimurium: a new medium for their isolation and new mutant classes. 39 18

In E. coli K12 (F'nif+Kp) hybrids, electron-transport-dependent phosphorylation is not necessary for anaerobic nitrogen fixation, and substrate level phosphorylation can provide sufficient ATP from glucose for nitrogenase activity. The fumarate-reduction system, however, is essential in these hybrids for the transfer of electrons to nitrogenase. This system is probably also involved in maintaining the membrane in the energized state, thereby allowing nitrogen fixation to occur. The nitrate-reduction system, which can energize the membrane like the fumarate-reduction system, is not necessary for nitrogenase activity in the E. coli K12(F'nif+Kp) hybrids. However, two nitrate reductase genes, chlA, and chlB, are essential for inhibition of nitrogen fixation by nitrate. Moreover, nitrate inhibits nitrogenase activity and this inhibition is most probably effected through a regulator factor coded by chlA and chlB.
 ...
PMID:Pathways of energy metabolism required for phenotypic expression of nif+Kp genes in Escherichia coli. 39 94

Spontaneous chlorate-resistant (Clr) mutants of three classes were isolated from Nostoc muscorum under three different selective conditions. A Clr-N2 class of mutants lacked nitrate reductase and showed nitrate inhibition of nitrogen fixation. A Clr-NO3 group of het+ nif- mutants formed heterocysts, but lacked nitrogen fixation and active nitrogenase enzyme. The Clr-NO2 class included those mutants deficient in both active nitrogenase and nitrate reductase, as they were unable to grow at the expense of molecular nitrogen or with nitrate nitrogen. The results suggest a common genetic determinant of active nitrogenase and nitrate reductase in the blue-green alga N. muscorum.
 ...
PMID:Isolation and characterization of chlorate-resistant mutants of the blue-green alga Nosoc muscorum. 40 80

At dissolved oxygen tensions of 15 mmHg (2 kPa) and below, nitrate-limited continuous cultures of Klebsiella K312 synthesized nitrate reductase (NR) and nitrite reductase (NiR) and excreted ammonia. Under anaerobic conditions over 60% of the nitrate-nitrogen utilized was excreted as ammonia. In contrast, carbon-limited cultures excreted nitrite at dissolved oxygen tensions of 15 mmHg or below and synthesized NR but not NiR. Ammonia repressed neither NR nor NiR synthesis. These observations indicate that below a critical oxygen tension of 15 mmHg Klebsiella K312 utilizes oxygen and nitrate as electron acceptors. This oxygen tension correlates well with the critical oxygen tension observed for a change from oxidative to fermentative metabolism in cultures of Klebsiella aerogenes. The product of dissimilatory nitrate reduction is ammonia in nitrate-limited cultures but principally nitrite in carbon-limited (nitrate excess) cultures.
 ...
PMID:Influence of oxygen tension on nitrate reduction by a Klebsiella sp. growing in chemostat culture. 47 38

Fours strains of nitrate reducing bacteria isolated from soil were studied for their behavior towards chlorate. They are facultative anaerobes, except for Bacillus megatherium (which is a strict aerobe) and they possess a nitrate reductase A. The growth of three strains of bacteria (Klebsiella pneumoniae, B. licheniformis and Micromonospora globosa) was slowed by sodium chlorate at a concentration of 0.06 to 0.1% while the other strain (B. megatherium) tolerated the CIO3- well. The delay of bacterial growth due to chlorate lasts for a certain period, after which the bacteria multiply again. The lag phase is due to small quantities of chlorite produced from the chlorate; the growth phase which follows is provoked by the multiplication of chlorate resistant mutants, most often nitrate reductase-negative and sometimes positive. Some reverse mutants nitrate reductase positive of K. pneumoniae no longer had the same characteristics as the wild strain: some resisted to chlorate or were different as to gas formation. The reduction of nitrate to ammonia by these bacteria is diminished in the presence of chlorate: the reduction of nitrate to nitrite was inhibited or not inhibited according to the type of strain. The bacteria broke down the chlorate partially or completely, according to the strains and the sustrates.
 ...
PMID:[A study of the action of sodium chlorate on strains of nitrate reducing soil bacteria (author's transl)]. 48 91

Assimilatory nitrate reductase (EC 1.6.6.1 NADH:nitrate oxidoreductase) from Chlorella vulgaris purified by affinity chromatography was found to be homogeneous as judged by electrophoresis on sodium dodecyl sulfate-polyacrylamide gel and by analytical ultracentrifugal techniques. The molecular weight of the intact enzyme and that of the enzyme dissociated in 6 M GuHCl, determined by sedimentation equilibrium studies, were 280,000 +/- 10,000 and 90,000 +/- 5,000, respectively. Comparable values were obtained using the S20,w value and the D20,w values in Svedberg's equation. The D20,w values were determined by laser light-scattering measurements. Active enzyme centrifugation showed that the monomer is an active species. A quantitative re-evaluation of the prosthetic groups present (FAD, heme, and molybdenum) was also made and was consistent with the conclusion that the active monomer contains three subunits as previously deduced by Solomonson et al. ((1975) J. Biol. Chem. 250, 4120). Electron micrographs showed images which corresponded to three subunits, supporting the data obtained by hydrodynamic studies. The enzyme is not cigar-shaped, as previously surmised, but has a roughly globular structure.
 ...
PMID:Physical studies on assimilatory nitrate reductase from Chlorella vulgaris. 50 Jun 68

Cell extract from a strain of Propionibacterium acidi-propionici with high nitrate reductase (NaR) activity catalyzed nitrate reduction with glycerol phosphate, NADH, or lactate. The reaction was inhibited partially by fumarate or oxygen. NaR linked to methyl viologen was found mostly in particulate fractions. It was solubilized by treatment with Emulgen 810 and purified 46-fold by DEAE-cellulose, Sepharose 4B, and triple DEAE-Sephadex chromatographies in the presence of the detergent. It was rather labile but was stabilized by glycerol. The molecular weight was estimated to be 230,000 by Sepharose 4B gel filtration and the isoelectric point was pH 5.0-5.5. The pH optimum was at 6.5-7.5 and Km for nitrate was 0.1 mM. As electron donors, methyl and benzyl viologen were utilized well but FAD and FMN were fairly ineffective. Chlorate was an active acceptor as well as nitrate. Azide, cyanide, and thiocyanate inhibited NaR. On adding 1 mM tungstate to the growing medium, the NaR level in grown cells was lowered; addition of 0.01 mM molybdate restored the activity partially. NaR is suggested to be a molybdo-protein, similar to this enzyme from other bacteria.
 ...
PMID:A study on nitrate reductase from Propionibacterium acidi-propionici. 62 3


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>