Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.27.1 (RNase)
16,360 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In order to elucidate the mechanism of action of Rhizopus niveus RNase Rh, we investigated the pH profiles of the kinetic parameters of RNase RNAP Rh, a derivative of RNase Rh, and its mutant enzymes, i.e., RNase RNAP Rh H104F, RNase RNAP Rh E105Q, and RNase RNAP Rh D51N. Based on comparisons of their profiles we concluded that protonation of His104 is indispensable for the enzymatic activity and Glu105 accelerates the enzymatic activity, especially at acid pH centered at pH 3.5. Based on these data and the previous data on the chemical modification and enzymatic properties of other mutant enzymes, we propose the following as a possible mechanisms of RNase Rh action. (i) His109 participates in enzymatic action as a general base catalyst which removes the hydrogen of the 2'-OH of the ribose moiety. (ii) His46 participates in the reaction as a general acid catalyst which interacts with the 5'-oxygen atom of the scissile phosphodiester bond and becomes a proton donor to the departing nucleoside or nucleotide. (iii) His104 interacts with phosphate anion and its protonation is favorable for the enzymatic activity. (iv) Since the protonated form of Glu105 is more favorable for activity, we postulate two possible roles for Glu105: (a) its stabilizes the intermediate, and (b) it interacts with the oxygen atom of P = O and polarizes the phosphorus atom.
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PMID:pH profile of kinetic constants of RNase Rh from Rhizopus niveus and its mutant enzymes towards UpU, and possible mechanisms of RNase Rh. 798 86

During the development of a procedure for the isolation of total genomic DNA from filamentous fungi (Rodriguez, R. J., and Yoder, O.C., Exp. Mycol. 15, 232-242, 1991) a cell fraction was isolated which inhibited the digestion of DNA by restriction enzymes. After elimination of DNA, RNA, proteins, and lipids, the active compound was purified by gel filtration to yield a single fraction capable of complete inhibition of restriction enzyme activity. The inhibitor did not absorb uv light above 220 nm, and was resistant to alkali and acid at 25 degrees C and to temperatures as high as 100 degrees C. More extensive analyses demonstrated that the inhibitor was also capable of inhibiting T4 DNA ligase and TaqI DNA polymerase, but not DNase or RNase. Chemical analyses indicated that the inhibitor was devoid of carbohydrates, proteins, lipids, and nucleic acids but rich in phosphorus. A combination of nuclear magnetic resonance, metachromatic shift of toluidine blue, and gel filtration indicated that the inhibitor was a polyphosphate (polyP) containing approximately 60 phosphate molecules. The mechanism of inhibition appeared to involve complexing of polyP to the enzymatic proteins. All species of Colletotrichum analyzed produced polyP equivalent in chain length and concentration. A modification to the original DNA extraction procedure is described which eliminates polyP and reduces the time necessary to obtain DNA of sufficient purity for restriction enzyme digestion and TaqI polymerase amplification.
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PMID:Polyphosphate present in DNA preparations from filamentous fungal species of Colletotrichum inhibits restriction endonucleases and other enzymes. 838 89

The hypothesis that ribosomes are present, but may have a restricted distribution, in the Mauthner (M) axon was evaluated in isolated M-cell axoplasm after (1) staining with YOYO-1 and (2) inspection by electron spectroscopic imaging (ESI) of ribosomal RNA (rRNA) phosphorus (P). Discrete periaxoplasmic plaques, identified by their ribonuclease-sensitive fluorescence, were located circumferentially at the surface boundary of isolated axoplasm and distributed longitudinally at random intervals. Conditions that destabilized plaques, and surface blotting of plaques onto a coverslip, revealed that fluorescent puncta were probably a significant source of plaque fluorescence. Fluorescent puncta were also distributed in a delimited volume of axoplasm, subjacent to the plaque. The notably higher density of F-actin in the latter region suggested that the actin cytoskeleton may govern the spatial distribution of puncta in subcortical axoplasm. Some fluorescent plaques were superficial to the cortical F-actin layer, whereas others formed inclusions within the F-actin layer; however, plaques did not appear to contain F-actin. Periaxoplasmic plaques were also identified in ordinary myelinated axons. ESI, in which rRNA emits bright signals in the phosphorus (P) spectral line against a low-contrast background, showed that isolated axoplasm contained characteristic 25 nm P signals, which were associated or in direct contact with a pleiomorphic structural matrix, located at the surface boundary. Polyribosomal P signals were also distributed in peripheral axoplasm below the matrix. The concept of a distinct polyribosome-populated domain, distributed intermittently in the cortical zone of the axon is described. This domain is spatially defined by a plaque-like periaxoplasmic structural matrix, and a confluent volume of subcortical axoplasm integrated through an actin cytoskeleton.
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PMID:Cortical plaque-like structures identify ribosome-containing domains in the Mauthner cell axon. 877 91

Chromium (Cr) at graded levels when added in sand culture of wheat (T. aestivum L. cv. UP2003) under glasshouse conditions resulted in reduction in biomass, chlorophyll and activities of catalase and peroxidase while enhanced acid phosphatase and ribonuclease activities. Elevated levels of Cr supply significantly reduced the concentration of inorganic phosphorus. With an increase in Cr supply the uptake of chromium also increased significantly in different plant parts especially in roots. Above metabolic lesions due to Cr in wheat provided evidence that the element in nutrient medium if present in excess may be inhibitory to plant growth and development.
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PMID:Chromium uptake and toxicity effects on growth and metabolic activities in wheat, Triticum aestivum L. cv. UP 2003. 897 7

The in situ distribution of phosphorus was studied in unstained ultrathin sections of salivary glands of Chironomus tentans and Ch. thummi larvae using elemental mapping by means of an energy-filtering transmission electron microscope. This distribution was related to the structures observed using contrast enhancement with inelastically scattered electrons at 250 eV. This procedure demonstrated that a phosphorus-containing fibril about 2 nm thick is the common substructure of the following nuclear ribonucleoprotein structural constituents: the Balbiani ring granules, their precursor fibrils seen at the sites of transcription, especially at the Balbiani rings, and the fibres traversing the pore of the nuclear envelope. These phosphorus-containing thin fibrils are sensitive to RNase. Thicker substructural features of the Balbiani ring granules, occurring as a curved ribbon on a dense particle, appear to be formed by the dense packing of the fine fibrils. The Balbiani ring granules located near the nuclear envelope are often linked to it by fine filaments.
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PMID:Electron spectroscopic imaging analyses of the distribution of phosphorus in Balbiani ring granules and in the surrounding nucleoplasm. 908 78

Plants have evolved elaborate metabolic and developmental adaptations to low phosphorus availability. Biochemical responses to phosphate limitation include increased production and secretion of phosphate-acquisition proteins such as nucleases, acid phosphatases, and high-affinity phosphate transporters. However, the signal transduction pathways that sense phosphate availability and integrate the phosphate-starvation response in plants are unknown. We have devised a screen for conditional mutants in Arabidopsis thaliana (L.) Heynh. to dissect signaling of phosphate limitation. Our genetic screen is based on the facultative ability of wild-type Arabidopsis plants to metabolize exogenous DNA when inorganic phosphate is limiting. After screening 50,000 M2 seedlings, we isolated 22 confirmed mutant lines that showed severely impaired growth on medium containing DNA as the only source of phosphorus, but which recovered on medium containing soluble inorganic phosphate. Characterization of nine such mutant lines demonstrated an inability to utilize either DNA or RNA. One mutant line, psr1 (phosphate starvation response), had significantly reduced activities of phosphate-starvation-inducible isoforms of ribonuclease and acid phosphatase under phosphate-limiting conditions. The data suggest that a subset of the selected mutations impairs the expression of more than one phosphate-starvation-inducible enzyme required for utilization of exogenous nucleic acids, and may thus affect regulatory components of a Pi starvation response pathway in higher plants.
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PMID:Conditional identification of phosphate-starvation-response mutants in Arabidopsis thaliana. 1092 99

A growing body of metabolic and molecular evidence of an endogenous protein-synthesizing machinery in the mature axon is a challenge to the prevailing dogma that the latter is dependent exclusively on slow axoplasmic transport to maintain protein mass in a steady state. However, evidence for a systematic occurrence of ribosomes in mature vertebrate axons has been lacking until recently, when restricted ribosomal domains, called "periaxoplasmic plaques," were described in goldfish CNS myelinated axons. Comparable restricted RNA/ribosomal "plaque" domains now have been identified in myelinated axons of lumbar spinal nerve roots in rabbit and rat on the basis of RNase sensitivity of YOYO-1-binding fluorescence, immunofluorescence of ribosome-specific antibodies, and ribosome phosphorus mapping by electron spectroscopic imaging (ESI). The findings were derived from examination of the axoplasm isolated from myelinated fibers as axoplasmic whole mounts and delipidated spinal nerve roots. Ribosomal periaxoplasmic plaque domains in rabbit axons were typically narrow ( approximately 2 microm), elongated ( approximately 10 microm) sites that frequently were marked by a protruding structure. The domain complexity included an apparent ribosome-binding matrix. The small size, random distribution, and variable intermittent axial spacing of plaques around the periphery of axoplasm near the axon-myelin border are likely reasons why their systematic occurrence has remained undetected in ensheathed axons. The periodic but regular incidence of ribosomal domains provides a structural basis for previous metabolic evidence of protein synthesis in myelinated axons.
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PMID:Cryptic peripheral ribosomal domains distributed intermittently along mammalian myelinated axons. 1106 46

When inorganic phosphate is limiting, Arabidopsis has the facultative ability to metabolize exogenous nucleic acid substrates, which we utilized previously to identify insensitive phosphate starvation response mutants in a conditional genetic screen. In this study, we examined the effect of the phosphate analog, phosphite (Phi), on molecular and morphological responses to phosphate starvation. Phi significantly inhibited plant growth on phosphate-sufficient (2 mM) and nucleic acid-containing (2 mM phosphorus) media at concentrations higher than 2.5 mM. However, with respect to suppressing typical responses to phosphate limitation, Phi effects were very similar to those of phosphate. Phosphate starvation responses, which we examined and found to be almost identically affected by both anions, included changes in: (a) the root-to-shoot ratio; (b) root hair formation; (c) anthocyanin accumulation; (d) the activities of phosphate starvation-inducible nucleolytic enzymes, including ribonuclease, phosphodiesterase, and acid phosphatase; and (e) steady-state mRNA levels of phosphate starvation-inducible genes. It is important that induction of primary auxin response genes by indole-3-acetic acid in the presence of growth-inhibitory Phi concentrations suggests that Phi selectively inhibits phosphate starvation responses. Thus, the use of Phi may allow further dissection of phosphate signaling by genetic selection for constitutive phosphate starvation response mutants on media containing organophosphates as the only source of phosphorus.
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PMID:Attenuation of phosphate starvation responses by phosphite in Arabidopsis. 1170 78

A new enzymatic method has allowed the assignment of the stereochemistry of E. coli RNase-H-assisted hydrolysis of RNA labelled within the scissile bond with (R(p))-phosphorothioate. This method is based on a stereospecific, two-step enzymatic conversion of cytidine 5'-[(18)O]phosphorothioate into the corresponding 5'-alpha-[(18)O]thiotriphosphate, which is then further used for stereospecific transfer of cytidine 5'-[(18)O]phosphorothioate to the 3'-OH group of a short oligonucleotide with the aid of terminal deoxyribonucleotidyl transferase. Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry of the resulting elongated primer revealed that RNase-H-assisted hydrolysis proceeds with inversion of configuration at the phosphorus atom. This result is discussed in the context of current knowledge of the architecture of the active site of the enzyme.
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PMID:Stereochemical course of Escherichia coli RNase H. 1246 33

The genotypic differences in P uptake efficiency of three rice varieties (IR74, IR71331 and IR71379) were studied under the P-deficiency condition with hydroponics, and their adaptability to low phosphorus stress about physio-biochemical mechanisms was further studied. The results showed that rice genotypes tolerated low P stress resulted from the co-ordination of P uptake efficiency, internal utilization efficiency and its translocation efficiency. The higher P-efficiency type IR74 and the middle type IR71331 had a higher P uptake efficiency. The rice genotype with higher P-efficiency was characterized by higher activity and desirable kinetic parameters of H2 PO4- uptake, showing lower Km and Cmin, but higher Imax values and relative APase activity, small amount of Km and Cmin. Moreover, under low P stress, the activity of RNase was about ten to fifteen times as high as that of the control (CK), but it had little genotypic differences.
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PMID:[Physiological adaptability of seeding rice genotypes with different P uptake efficiency under low P-deficient stress]. 1272 40


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