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PubMed2000

On the irreversible destruction of reduced nicotinamide nucleotides by hypohalous acids.

Degradation of the reduced pyridine nucleotides NMNH and NADH by HOCl involves two distinct stages: a fast reaction, k = 4.2 x 10(5) M(-1) s(-1), leads to generation of stable pyridine products (Py/Cl) with a strong absorption band at 275 nm (epsilon = 12.4 x 10(3) M(-1) cm(-1) in the case of NMNH); secondarily, a subsequent reaction of HOCl, k = 3.9 x 10(3) M(-1) s(-1), leads to a complete loss of the aromatic absorption band of the pyridine ring. HOBr and HOI(I(2)) react similarly. Apparent rate constants of the primary reactions of HOX species with NMNH at pH 7.2 increase in the order HOCl (3 x 10(5) M(-1) s(-1)) < HOBr( approximately 4 x 10(6) M(-1) s(-1)) < HOI(I(2))( approximately 6.5 x 10(7) M(-1) s(-1)). HOBr reacts fast also with the primary product Py/Br, k approximately 9 x 10(5) M(-1) s(-1), while the reactions of HOI and I(2) with Py/I are slower, approximately 1.4 x 10(3) M(-1) s(-1) and >6 x 10(3) M(-1) s(-1), respectively. Halogenation of the amide group of NMN(+) by HOX species is many orders of magnitude slower than oxidation of NMNH. Taurine inhibits HOCl-induced oxidation of NADH, but HOBr-induced oxidation is not inhibited because the taurine monobromamine rapidly oxidizes NADH, and oxidation by HOI(I(2)) is not inhibited because taurine is inert toward HOI(I(2)). Also sulfur compounds (GSH, GSSG, and methionine) are less efficient in protecting NADH against oxidation by HOBr and HOI(I(2)) than against oxidation by HOCl. The results suggest that reactions of HOBr and HOI(I(2)) in a cellular environment are much more selectively directed toward irreversible oxidation of NADH than reactions of HOCl. It is noteworthy that the rather inert N-chloramines react with iodide to generate HOI(I(2)), i.e., the most reactive and selective oxidant of reduced pyridine nucleotides. NMR investigations show that the primary stable products of the reaction between NMNH and HOCl are various isomeric chlorohydrins originating from a nonstereospecific electrophilic addition of HOCl to the C5&dbond;C6 double bond of the pyridine ring. The primary products (Py/X) of NMNH all exhibit similar absorption bands around 275 nm and are hence likely to result from analogous addition of HOX to the C5&dbond;C6 bond of the pyridine ring. Since the Py/X species are stable and inert toward endogeneous reductants like ascorbate and GSH, they may generally be useful markers for assessing the contribution of hypohalous acids to inflammatory injury.

Bromates↗
PubMed1994

Interaction of basic fibroblast growth factor (FGF-2) with nonresponsive HeLa cells.

Human HeLa adenocarcinoma cells did not respond to basic fibroblast growth factor (bFGF or FGF-2) but did bind the same amount of bFGF as responsive Chinese hamster lung fibroblasts (CCL 39). Heparinase II treatment of HeLa and CCL 39 cells resulted in a decrease of bFGF binding by 96 and 57%, respectively, indicating that heparan sulfate molecules were involved in bFGF binding. On HeLa cells, bFGF bound to a single family of low-affinity sites. Cross-linking experiments of 125I-bFGF to HeLa cells yielded several labeled complexes. Cell-associated 125I-bFGF was internalized in both cell types either by high-affinity receptors and heparitinase-sensitive sites in CCL 39 cells or by heparitinase-sensitive binding sites only in HeLa cells. The binding of bFGF to nonresponsive HeLa cells and its internalization via a family of heparitinase-sensitive binding sites might illustrate other functions of bFGF unrelated to cell proliferation.

Animals↗
PubMed1993

Circadian and light-regulated expression of nitrate reductase in Arabidopsis.

The expression of a number of plant genes is regulated by an endogenous circadian clock. We report that the Arabidopsis NIA2 (nitrate reductase) gene shows robust circadian oscillations in mRNA accumulation which persist for at least 5 days in plants that have been grown in a light-dark (LD) cycle and then transformed to continuous light (LL). We further show that NIA2 mRNA accumulation oscillates in a circadian fashion in plants that have been grown in LD and then transferred to continuous darkness (DD). Results from nuclear run-on transcriptional analysis suggest that the oscillations in steady-state levels of NIA2 mRNA abundance are not primarily due to changes in transcription but, instead, reflect post-transcriptional regulation. The circadian oscillations in NIA2 mRNA abundance are paralleled by circadian oscillations in nitrate reductase enzyme activity (NR activity) in Arabidopsis plants that have been grown in LD and then transferred either to DD or to LL. Etiolated Arabidopsis seedlings express neither NIA2 mRNA nor NR activity. However, both NIA2 mRNA accumulation and NR activity are induced by exposure to white light. The inductive effects of light on NIA2 mRNA accumulation are due, at least in part, to a very low fluence phytochrome-mediated response. However, the persistence of circadian oscillations in NIA2 mRNA abundance for at least 5 days in LL demonstrates that the circadian clock is capable of overriding or gating the inductive effects of light on NIA2 mRNA accumulation in Arabidopsis for an extended, continuous period of time.

Arabidopsis↗
PubMed1994

Nitrate reductase of the ascomycetous fungus, Leptosphaeria maculans: gene sequence and chromosomal location.

The nitrate reductase (niaD) gene was isolated from the phytopathogenic loculoascomycete Leptosphaeria maculans by screening a genomic DNA library with the Aspergillus nidulans niaD gene. The L. maculans niaD gene is the first protein-encoding gene characterised from this fungus. It encodes a predicted protein of 893 amino acids and contains four putative introns at positions in the gene equivalent to those of four of the six introns in the A. nidulans niaD gene. Mutants defective in niaD and molybdenum cofactor gene(s) of L. maculans have been isolated. Transformation of a L. maculans niaD mutant with a 3.8 kb SacII fragment containing the L. maculans niaD gene restored wild-type growth on nitrate as a sole nitrogen source. The niaD gene is present as a single copy on a chromosome which ranges in size from 2.6 to 2.8 Mb between the different L. maculans isolates examined.

Amino Acid Sequence↗
PubMed1987

Cloning of seven differently complementing DNA fragments with chl functions from Escherichia coli K12.

Seven genomic libraries of chromosomal Escherichia coli K12 wild-type DNA were constructed in plasmid vectors. These were used to transform chl insertion mutants. Selection for growth on nitrate under anaerobic conditions yielded four plasmids which complemented mutants of the chlA, B, E and G types. The chromosomal fragments were mapped with restriction enzymes and subcloned. Three complementation groups were observed among the chlA mutants and two among the chlE mutants. The established complementation groups plus mutants of the chlD type represent eight distinct functions, which are all believed to be required for the molybdenum cofactor activity in the reduction of nitrate to nitrite by E. coli.

Chlorates↗
PubMed1975

The nitrate-reducing enzyme system of Chlamydomonas reinhardii.

In Chlamydomonas reinhardii the reduction of nitrate to ammonia occurs in two independent enzymatic steps: 1. the two-electrons reduction of nitrate to nitrite catalyzed by NADH-nitrate reductase, and, 2. the six-electrons reduction of nitrite to ammonia catalyzed by ferredoxin-nitrite reductase. Both enzymes have been purified and characterized, and some of their properties have been studied.

Azides↗
PubMed1980

Effects of molybdenum and tungsten on induction of nitrate reductase and formate dehydrogenase in wild type and mutant Paracoccus denitrificans.

Molybdenum is required for induction of nitrate reductase and of NAD-linked formate dehydrogenase activities in suspensions of wild type Paracoccus denitrificans; tungsten prevents the development of these enzyme activities. The wild type forms a membrane protein Mr150,000 when incubated with tungsten and inducers of nitrate reductase and this is presumed to represent an inactive form of the enzyme. Suspensions of mutuant M-1 did not develop nitrate reductase or formate dehydrogenase activities but the membrane protein Mr150,000 was formed under all conditions tested, including without inducers and without molybdenum. Analysis of membranes, solubilized with deoxycholate, by polyacrylamide gel electrophoresis under nondenaturing conditions showed that the mutant protein had similar electrophoretic mobility to the active nitrate reductase formed by the wild type. Autoradiography of preparations from cells incubated with 55Fe showed that the mutant and wild type proteins contained iron. However, in similar experiments with 99Mo, incorporation of molybdenum into the mutant protein was not detectable. We conclude that mutant M-1 is defective in one or more steps required to process molybdenum for incorporation into molybdoenzymes. This failure affects the normal regulation of nitrate reductase protein with respect to the role of inducers.

Aldehyde Oxidoreductases↗
PubMed1991

Horse heart ferricytochrome c: conformation and heme configuration of high ionic strength acidic forms.

The absorption, circular dichroism, and resonance Raman spectra of horse heart ferricytochrome c in the presence of 0.2 M KCl, 0.1 M NaClO4, and 0.2 M KNO3, in the pH region 7 to 0.5, have been investigated to determine the nature and the course of the processes involved. As in the absence of salts (Myer, Y., and Saturno, A. F. (1990) J. Protein Chem, 9, 379-387), the change from neutral to low acidic pH's in the presence of salts is a three-step process: state IIIs----state IIIS,a----state IIS----state IS, with pKa's of 3.5 +/- 0.2, 2.2 +/- 0.2, and 1.1 +/- 0.2, and with two, one, and one number of protons, respectively. The addition of salts at neutral pH's has little or no effect on the protein conformation and the heme-iron configuration (i.e., they remain the same, low-spin hexacoordinated heme iron with a Met-80-Fe-His-18 axial coordination), but such addition does cause a slight tightening of the heme crevice and the enlargement of the porphyrin core. State IIIS,a is a folded state with about the same degree of folding and with a similar spin state and coordination configuration of iron, but the heme crevice is loosened and the porphyrin core is smaller. Both states IIS and IS are also essentially folded forms, but with a smaller degree of protein secondary structure. State IIS has a high-spin hexacoordinated heme iron with a water molecular and a protonated and/or hydrogen-bonded imidazole of his-18 as the two axial ligates; and state IS has a high-spin pentacoordinated heme iron, which is about 0.49 A out of the porphyrin plane, with a protonated and/or hydrogen-bonded imidazole nitrogen as the only axial ligate. The addition of anions causes the stabilization of the protein secondary structures and the state IIIa----state II transition. The mode of effectiveness of anions appears to be nonspecific (i.e., because of electrostatic shielding and/or disruption of salt bridges).

Animals↗
PubMed1993

Gene manipulation by protoplast fusion and penicillin production by Penicillium chrysogenum.

Hybrids have been obtained by protoplast fusion of nitrate-nonutilizing cnx- and acetate-nonutilizing fac- mutants of Penicillium chrysogenum strains 4/95 and 26/818, respectively. Induced haplodization of the hybrids allowed the recovery of stable segregants, which were screened for penicillin production. The penicillin-producing segregants showed a wide range of titers that reached for a certain mutant to 290-390% increase above the parent strains.

Chlorates↗
PubMed2001

Eukaryotic nitrate and nitrite transporters.

Nitrate transport is the key step controlling the amount of nitrate incorporated by the cells and subsequent of storage, reduction or export. Molecular, genetic and biochemical approaches to the study of eukaryotic nitrate/nitrite transporters allow an initial understanding of this step, which is much more complex and structured than previously suspected. At the plasma membrane level, two gene families, Nrt1 and Nrt2, account for high- and low-affinity nitrate transporters. Functionality of NRT1 from Arabidopsis and NRT2 proteins from Aspergillus and Chlamydomonas has been demonstrated. However, redundancy of these systems makes it difficult to assign particular physiological roles to each. Data on genes involved in the regulation of nitrate transport and reduction are still scarce. Information on nitrite transporters to the chloroplast is biased by the belief that in vivo nitrous acid diffuses freely to this organellum. The recent progress on these aspects is discussed in this review.

Amino Acid Sequence↗
PubMed2005

Effect of Lomodex-MgSO(4) in the prevention of reperfusion injury following unilateral testicular torsion: an experimental study in rats.

Fertility in patients treated for unilateral testicular torsion has been shown to be significantly reduced in all the reported series to date, implying that the present-day treatment requires further refinement in the form of adjunct pharmacotherapeutic intervention (Lomodex and MgSO(4)) in addition to scrotal exploration. Prepubertal Holtzman strain rats (35 days old) were used for our study. Two sets were formed with six groups of rats in each set. Rats were treated as follows: group 1, sham-operated group; group 2, torsion (4 h); group 3, torsion + detorsion (1 h); group 4, torsion + ATP-MgCl(2) + detorsion; group 5, torsion + Lomodex-MgSO(4) + detorsion; group 6, torsion + normal saline + detorsion. Whereas the first set of animals was sacrificed immediately at the end of experiment, animals in set 2 were sacrificed 8 weeks after the end of the experiment to look for the development of antisperm antibodies. Parameters studied were thiobarbituric acid reductase (TBAR) assay, histology of testicular tissue, and sperm agglutination test. Student's t-test was used for significance. With detorsion (149.95+/-30.68) there was a significant rise in the TBAR values (P<0.05) compared with torsion (57.39+/-14.47). Treatment with both Lomodex-MgSO(4) (40.74+/-6.39) and ATP-MgCl(2) (48.30+/-18.35) yielded TBAR levels comparable to those in the sham group (31.35+/-11.96). Similar injury was also seen on the contralateral testis, with detorsion (114.28+/-10.68) much more detrimental than torsion (40.59+/-15.02) and rescue seen following treatment with Lomodex-MgSO(4) (27.55+/-8.64) as well as ATP-MgCl(2) (38.61+/-12.23). Regarding th histology, with detorsion there was evidence of severe distortion of tubules, with almost all the tubules showing maturation arrest and a few tubules completely devoid of any germinal cells. Treatment with Lomodex-MgSO(4) as well as ATP-MgCl(2) showed preservation of tubular morphology. Our study failed to document the presence of agglutinating antibodies (antisperm antibodies) in any of the groups. Unilateral testicular torsion has bilateral effects and is a form of ischemia-reperfusion injury. Treatment of torsion by detorsion alone does not prevent testicular damage. The results of the present study show that administration of Lomodex + MgSO(4) prior to detorsion results in prolonged testicular salvage with a potential of subsequent improvement in semen quality and fertility and reduction in long-term morbidity. The presence of agglutinating antibodies could not be detected in the present study.

Adenosine Triphosphate↗