Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.26.9 (ribonuclease)
 6,589 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The formation of a stable complex between glutamyl-tRNA synthetase and the first enzyme of chlorophyll biosynthesis glutamyl-tRNA reductase was investigated in the green alga Chlamydomonas reinhardtii. Apparently homogenous enzymes, purified after previously established purification protocols were incubated in various combinations with ATP, glutamate, tRNA(Glu) and NADPH and formed complexes were isolated via glycerol gradient centrifugation. Stable complexes were detected only after the preincubation of glutamyl-tRNA synthetase, glutamyl-tRNA reductase with either glutamyl-tRNA or free tRNA(Glu), ATP and glutamate, indicating the obligatory requirement of aminoacylated tRNA(Glu) for complex formation. The further addition of NADPH resulting in the reduction of the tRNA-bound glutamate to glutamate 1-semialdehyde led to the dissociation of the complex. Once complexed to the two enzymes tRNA(Glu) was found to be partially protected from ribonuclease digestion. Escherichia coli, Bacillus subtilis and Synechocystis 6803 tRNA(Glu) were efficiently incorporated into the protein-RNA complex. The detected complexes provide the chloroplast with a potential channeling mechanism for Glu-tRNA(Glu) into chlorophyll synthesis in order to compete with the chloroplastic protein synthesis machinery.
 ...
PMID:Complex formation between glutamyl-tRNA synthetase and glutamyl-tRNA reductase during the tRNA-dependent synthesis of 5-aminolevulinic acid in Chlamydomonas reinhardtii. 145 6

Thioredoxin (Trx) from Escherichia coli was compared with bovine protein disulfide-isomerase (PDI) for its ability to catalyze native disulfide formation in either reduced or randomly oxidized (scrambled) ribonuclease A (RNase). On a molar basis, a 100-fold higher concentration of Trx than of PDI was required to give the same rate of native disulfide formation measured as recovery of RNase activity. A Pro-34 to His (P34H Trx) mutation in the active site of E. coli Trx (WCGPC), mimicking the two suggested active sites in PDI (WCGHC), increased the catalytic activity in disulfide formation about 10-fold. The mutant P34H Trx displayed a 35-mV higher redox potential (E'0) of the active site disulfide/dithiol relative to wild type Trx, making it more similar to the redox potential observed for PDI. This higher redox potential correlates well with the enhanced activity and suggests a role for the histidine side chain. Enzymatic isomerization of disulfides in scrambled, oxidized RNase requires the presence of a catalytic thiol such as GSH to initiate the thiol-disulfide interchange. Bovine thioredoxin reductase, together with NADPH, could replace GSH. For oxidative folding of reduced RNase in air with Trx, P34H Trx, or PDI, catalytic amounts of sodium selenite (1 microM) resulted in rapid disulfide formation and high yields of ribonuclease activity equivalent to previously known redox buffers of GSH and GSSG. These results demonstrate no obligatory role for glutathione in disulfide formation. A possible mechanism for the unknown thiol oxidative process accompanying folding and protein disulfide formation in vivo is discussed.
 ...
PMID:A Pro to His mutation in active site of thioredoxin increases its disulfide-isomerase activity 10-fold. New refolding systems for reduced or randomly oxidized ribonuclease. 157 42

The in vitro metabolism of [14C]toluene by liver microsomes and liver slices from male Fischer F344 rats and human subjects has been compared. Rat liver microsomes produced only benzyl alcohol from toluene. Liver microsomes from human subjects metabolized toluene to benzyl alcohol, benzaldehyde, and benzoic acid. Liver microsomes from one human donor also produced p-cresol and o-cresol. The overall rate of toluene metabolism by human liver microsomes was 9-fold greater than by rat liver microsomes. Human liver microsomal metabolism of benzyl alcohol to benzaldehyde required NADPH and was inhibited by carbon monoxide and high pH (pH 10). but was not inhibited by ADP-ribose or sodium azide. These results suggest that cytochrome P-450, rather than alcohol dehydrogenase, was responsible for the metabolism of benzyl alcohol to benzaldehyde. Human and rat liver slices metabolized toluene to hippuric acid and benzoic acid. The overall rate of toluene metabolism by human liver slices was 1.3-fold greater than by rat liver slices. Cresols and cresol conjugates were not detected in human or rat liver slice incubations. Covalent binding of [14C]toluene to human liver microsomes and slices was 21-fold and 4-fold greater than to the comparable rat liver preparations. Covalent binding did not occur in the absence of NADPH, was significantly decreased by coincubation with cysteine, glutathione, or superoxide dismutase, and was unaffected by coincubation with lysine. Protease and ribonuclease digestion decreased the amount of toluene covalently bound to human liver microsomes by 78% and 27% respectively. Acid washing of human liver microsomes had no effect on covalent binding.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Metabolism and covalent binding of [14C]toluene by human and rat liver microsomal fractions and liver slices. 198 39

Superoxide radical (O2-) is ubiquitously critical to the bioactivity of endothelial nitric oxide. In angiotensin-dependent hypertension, vascular O2- levels rise and impede endothelium/nitric oxide-dependent vascular relaxation. We have reported that the major O2- source in the rabbit aorta is adventitial fibroblast phagocyte-like NADPH oxidase and shown that angiotensin (Ang) II treatment of adventitial fibroblasts causes a concentration-dependent increase in particulate NADPH-dependent O2-. From cultured rabbit aortic adventitial fibroblasts treated or not treated with Ang II, we prepared particulate fractions and measured lucigenin-enhanced chemiluminescence. Because [Sar1,Thr8]-Ang II, a generalized antagonist of Ang II and plausible inhibitor of the conversion of Ang II, reversed Ang II (10 nmol/L)-induced NADH- and NADPH-dependent O2- to basal levels, we tested the effect of the inhibitor of aminopeptidase N, amastatin (10 micromol/L), and found no effect on Ang II-stimulated O2-. Ang(1-7), Ang III, and Ang IV also were not effective in stimulating O2- levels at concentrations similar to those of Ang II. Kinetic analysis showed a rise in NADPH oxidase O2- production in response to Ang II, which peaks at 3 hours and returns to basal levels by 16 hours. p67phox, a cytosolic factor, appears to be affected at both the level of transcription and protein synthesis because actinomycin and cycloheximide individually inhibited the observed effect. A partial sequence of p67phox was recovered by reverse transcriptase from mRNA harvested from cultured rabbit aortic adventitial fibroblasts. Furthermore, the p67phox mRNA transcript in aortic fibroblasts is induced by Ang II before the peak of NADPH oxidase by Northern analysis and ribonuclease protection assays. These data suggest that Ang II stimulates NAD(P)H oxidase O2- generation in fibroblasts of aortic adventitia via transcriptional activation of p67phox. These data also provide preliminary evidence for the regulation of factors of the NADPH oxidase and potentially provide a novel means by which to abrogate the development of O2(-)-dependent hypertension.
 ...
PMID:Angiotensin II induces p67phox mRNA expression and NADPH oxidase superoxide generation in rabbit aortic adventitial fibroblasts. 971 63

A cDNA encoding a cytochrome P450 enzyme was isolated from a cDNA library of the corpora allata (CA) from reproductively active Diploptera punctata cockroaches. This P450 from the endocrine glands that produce the insect juvenile hormone (JH) is most closely related to P450 proteins of family 4 and was named CYP4C7. The CYP4C7 gene is expressed selectively in the CA; its message could not be detected in the fat body, corpora cardiaca, or brain, but trace levels of expression were found in the midgut and caeca. The levels of CYP4C7 mRNA in the CA, measured by ribonuclease protection assays, were linked to the activity cycle of the glands. In adult females, CYP4C7 expression increased immediately after the peak of JH synthesis, reaching a maximum on day 7, just before oviposition. mRNA levels then declined after oviposition and during pregnancy. The CYP4C7 protein was produced in Escherichia coli as a C-terminal His-tagged recombinant protein. In a reconstituted system with insect NADPH cytochrome P450 reductase, cytochrome b5, and NADPH, the purified CYP4C7 metabolized (2E,6E)-farnesol to a more polar product that was identified by GC-MS and by NMR as (10E)-12-hydroxyfarnesol. CYP4C7 converted JH III to 12-trans-hydroxy JH III and metabolized other JH-like sesquiterpenoids as well. This omega-hydroxylation of sesquiterpenoids appears to be a metabolic pathway in the corpora allata that may play a role in the suppression of JH biosynthesis at the end of the gonotrophic cycle.
 ...
PMID:A cytochrome P450 terpenoid hydroxylase linked to the suppression of insect juvenile hormone synthesis. 978 9

Mammalian thioredoxin reductase (TRR; NADPH(2):oxidized thioredoxin oxidoreductase, E.C. 1.6.4.5) is a new member of the family of selenocysteine-containing proteins. TRR activity in Se-deficient rat liver is reported to decrease to 4.5 to 15% of the activity in Se-adequate rat liver, similar to the fall in Se-dependent glutathione peroxidase-1 activity. Both glutathione peroxidase-1 enzyme activity and mRNA levels decrease dramatically in Se deficiency, whereas glutathione peroxidase-4 activity only decreases to 40% of Se-adequate levels and mRNA level is little affected by Se deficiency. The purpose of these experiments is to study the effect of Se status on TRR mRNA levels and enzyme activity in our well-characterized rat model, and to compare this regulation directly to the regulation of other Se-dependent proteins in male weanling rats fed Se-deficient diets or supplemented with dietary Se for 28 days. In two experiments, TRR activity in Se-deficient liver decreased to 15% of Se-adequate activity as compared to 2% and 40% of Se-adequate levels for GPX1 and GPX4, respectively. Using ribonuclease protection analysis, we found that TRR mRNA levels in Se-deficient rat liver decreased to 70% of Se-adequate levels. This decrease in TRR mRNA was similar to the GPX4 mRNA decrease in Se-deficient liver in these experiments, whereas GPX1 mRNA levels decreased to 23% of Se-adequate levels. This study clearly shows that TRR represents a third pattern of Se regulation with dramatic down-regulation of enzyme activity in Se deficiency but with only a modest decrease in mRNA level. The conservation of TRR mRNA in Se deficiency suggests that this is a valued enzyme; the loss of TRR activity in Se deficiency may be the cause of some signs of Se deficiency.
 ...
PMID:Selenium regulation of thioredoxin reductase activity and mRNA levels in rat liver. 1203 Dec 52

Pollack, J. D. (University of Connecticut, Storrs), Shmuel Razin, and Robert C. Cleverdon. Localization of enzymes in Mycoplasma. J. Bacteriol. 90:617-622. 1965.-Cells of eight parasitic and two saprophytic Mycoplasma strains were lysed by use of osmotic shock, and the membranes were separated from the soluble fraction by use of differential centrifugation. Cell fractions were tested for reduced nicotinamide adenine dinucleotide (NADH(2)) oxidase, reduced nicotinamide adenine dinucleotide phosphate (NADPH(2)) oxidase, glucose-6-phosphate dehydrogenase, adenosine triphosphatase, ribonuclease, and deoxyribonuclease activities. Adenosine triphosphatase was confined to the membrane fraction of all Mycoplasma strains. The NADH(2) oxidase activity was associated with the membranes of the saprophytic M. laidlawii and with the soluble fraction of the parasitic Mycoplasma strains. NADPH(2) oxidase activity was detected only in the soluble fraction of the parasitic strains. Glusose-6-phosphate dehydrogenase was demonstrated only in the soluble fraction of M. laidlawii. Ribonuclease activity was found usually in both membrane and soluble fractions, but was generally higher in the membrane fraction. In the human and bovine Mycoplasma strains, deoxyribonuclease activity could not be demonstrated in the soluble fraction; in the remaining strains, activity was highest in the soluble fraction. Dissolution of M. laidlawii strain B membranes by sodium deoxycholate significantly increased membrane-NADH(2) oxidase and adenosine triphosphatase activities.
 ...
PMID:Localization of Enzymes in Mycoplasma. 1656 57

5-Aminolevulinic acid synthesis in isolated, intact, developing chloroplasts from greening cucumber (Cucumis sativus) cotyledons was inhibited by broken chloroplast fragments. It was shown that the inhibitory constituent was associated with the thylakoid membrane system. The inhibitor was resistant to boiling, was not a form of ribonuclease, and did not inhibit Mg-chelatase, indicating that massive organelle destruction was not involved. The inhibitor was also found in etioplast and mature chloroplasts; and it was found in barley as well as cucumber. 5-Aminolevulinate synthesis in the dark with exogenous ATP and NADPH, or in the light without added cofactors, were inhibited approximately equally. In the dark, 5-aminolevulinate synthesis and protochlorophyllide synthesis from glutamate were inhibited to about equal extent. The inhibition was decreased when the membranes were washed with aqueous acetone prior to incubation. The inhibition by the unknown factor was compared to the inhibition by gabaculine, 4-amino-5-hexynoic acid, protoheme, and glutathione. The unknown inhibitor appeared to have a number of similarities with protoheme.
 ...
PMID:Regulation of 5-Aminolevulinic Acid Synthesis in Developing Chloroplasts : IV. An Endogenous Inhibitor from the Thylakoid Membranes. 1666 54

An intimate link exists between circadian clocks and metabolism with nearly every metabolic pathway in the mammalian liver under circadian control. Circadian regulation of metabolism is largely driven by rhythmic transcriptional activation of clock-controlled genes. Among these output genes, Nocturnin (Noct) has one of the highest amplitude rhythms at the mRNA level. The Noct gene encodes a protein (NOC) that is highly conserved with the endonuclease/exonuclease/phosphatase (EEP) domain-containing CCR4 family of deadenylases, but highly purified NOC possesses little or no ribonuclease activity. Here, we show that NOC utilizes the dinucleotide NADP(H) as a substrate, removing the 2' phosphate to generate NAD(H), and is a direct regulator of oxidative stress response through its NADPH 2' phosphatase activity. Furthermore, we describe two isoforms of NOC in the mouse liver. The cytoplasmic form of NOC is constitutively expressed and associates externally with membranes of other organelles, including the endoplasmic reticulum, via N-terminal glycine myristoylation. In contrast, the mitochondrial form of NOC possesses high-amplitude circadian rhythmicity with peak expression level during the early dark phase. These findings suggest that NOC regulates local intracellular concentrations of NADP(H) in a manner that changes over the course of the day.
 ...
PMID:Spatiotemporal regulation of NADP(H) phosphatase Nocturnin and its role in oxidative stress response. 3187 54