Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.8 (polynucleotide phosphorylase)
 723 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An isotopic shift of the (31)P nuclear magnetic resonance due to (18)O bonded to phosphorus of 0.0206 ppm has been observed in inorganic orthophosphate and adenine nucleotides. Thus, the separation between the resonances of (31)P(18)O(4) and (31)P(16)O(4) at 145.7 MHz is 12 Hz and, in a randomized sample containing approximately 50% (18)O, all five (16)O-(18)O species are resolved and separated from each other by 3 Hz. Not only does this yield the (18)O/(16)O ratio of the phosphate but, more important, the (18)O-labeled phosphate in effect can serve as a double label in following phosphate reactions, for oxygen in all cases and for phosphorus, provided the oxygen does not exchange with solvent water. Thus, it becomes possible to follow labeled phosphorus or labeled oxygen continuously as reactions proceed. Rate studies involving (i) phosphorus and (ii) oxygen are illustrated by continuous monitoring of the exchange reactions between (i) the beta phosphate of ADP and inorganic phosphate catalyzed by polynucleotide phosphorylase and (ii) inorganic orthophosphate and water catalyzed by yeast inorganic pyrophosphatase. In the ADP-P(i) exchange, the P(i) ((18)O(4)) yielded an alpha P((16)O(3) (18)O) and a beta P((18)O(4)), proving that bond cleavage occurs between the alpha P and the alpha-beta bridge oxygen. Among the many additional potential uses of this labeling technique and its spectroscopic observation are: (i) different labeling of each phosphate group of ATP, (ii) to follow rate of transfer of (18)O from a nonphosphate compound such as a carboxylic acid to a phosphate compound, and (iii) to follow the rate of scrambling (for example, of the beta-gamma bridge oxygen of ATP to nonbridge beta P positions) and simultaneously the rate of exchange of the gamma P nonbridge oxygens with solvent water in various ATPase reactions.
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PMID:Isotopic (18O) shift in 31P nuclear magnetic resonance applied to a study of enzyme-catalyzed phosphate--phosphate exchange and phosphate (oxygen)--water exchange reactions. 20 29

The release of lipoteichoic acid and mesosomal vesicles to the supernatant buffer during the formation of spherical, osmotically fragile bodies was studied using Streptococcus faecalis ATCC 9790. Autolytic N-acetylmuramidase action was permitted to take place in exponential-phase cells incubated in a buffer which provides an exceptional degree of osmotic stabilization. Both lipoteichoic acid and mesosomal vesicles were relatively rapidly released to the supernatant buffer. Most of the cellular content of lipoteichoic acid (and mesosomal vesicles) was found in the supernatant buffer at incubation times when the cells still retained over 75% of their cell wall. [14-C]- or [3-H]glycerol was used as a label for both cellular lipoteichoic acids and lipid-glycerol. Glycerol in lipoteichoic acid was quantitated after phenol-water and chloroform-methanol treatments and identified by products of acid hydrolysis and its ability to be precipitated by (i) antibodies specific for the polyglycerol-phosphate backbone, (ii) antibodies to the streptococcal group D antigen, and (iii) concanavalin A. Evidence was obtained that lipoteichoic acid was not associated with isolated mesosomal vesicles. Centrifugation of supernates at 200,000 X g sedimented membranous (mesosomal) vesicles and nearly all of the lipid-glycerol present, whereas essentially all of the lipoteichoic acid remained in the supernatant. The sedimented mesosomal vesicles differed from protoplast membrane in their higher lipid-phosphorus to protein ratio and in the absence of detectable levels of two enzymatic activities found in protoplast membranes, adenosine triphosphatase and polynucleotide phosphorylase. Both types of membranes were found to contain DD-carboxypeptidase and LD-transpeptidase activities at nearly the same specific activities. No evidence was obtained for the association of autolytic N-acetylmuramidase activity with either type of membrane preparation.
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PMID:Cellular localization of lipoteichoic acid in Streptococcus faecalis. 80 56

The ADP analogue in which the 5'-oxygen has been replaced by a methylene group can be prepared by condensing 5'-deoxy-5'-phosphonomethyladenosine with inorganic phosphate. This analogue readily polymerizes onto the primer A-A in the presence of the enzyme polynucleotide phosphorylase and either Mg2+ or Mn2+. The initial products are of the form A-A(-cA)n-cA (where "-" and "-c" stand for the normal phosphodiester linkage and the linkage in which the 5'-oxygen is replaced with the methylene group, respectively). Treatment of these with alkali yields adenosine 2'(3')-phosphate and the series (A(-cA)n-cA containing only phosphonomethylene linkages. The decamer A(-cA)8-cA interacts with two molecules of U(-U)8-U to form a triple-standard structure that has a stability similar to that exhibited by the analogous complex formed from A(-A)8-A and U(-U)8-U. This property, along with the resistance of these oligomer analogues toward nucleases that cleave phosphodiester linkages between the phosphorus and the 5'-oxygen, should provide a strong rationale for application of phosphonomethylene linkages in schemes for therapeutic drug design that use the antisense strategy.
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PMID:Synthesis and properties of adenosine oligonucleotide analogues containing methylene groups in place of phosphodiester 5'-oxygens. 839 23

Cell survival depends on the cell's ability to acclimate to phosphorus (P) limitation. We studied the chloroplast ribonuclease polynucleotide phosphorylase (PNPase), which consumes and generates phosphate, by comparing wild-type Chlamydomonas reinhardtii cells with strains with reduced PNPase expression. In the wild type, chloroplast RNA (cpRNA) accumulates under P limitation, correlating with reduced PNPase expression. PNPase-deficient strains do not exhibit cpRNA variation under these conditions, suggesting that in the wild type PNPase limits cpRNA accumulation under P stress. PNPase levels appear to be mediated by the P response regulator PHOSPHORUS STARVATION RESPONSE1 (PSR1), because in psr1 mutant cells, cpRNA declines under P limitation and PNPase expression is not reduced. PNPase-deficient cells begin to lose viability after 24 h of P depletion, suggesting that PNPase is important for cellular acclimation. PNPase-deficient strains do not have enhanced sensitivity to other physiological or nutrient stresses, and their RNA and cell growth phenotypes are not observed under P stress with phosphite, a phosphate analog that blocks the stress signal. In contrast with RNA metabolism, chloroplast DNA (cpDNA) levels declined under P deprivation, suggesting that P mobilization occurs from DNA rather than RNA. This unusual phenomenon, which is phosphite- and PSR1-insensitive, may have evolved as a result of the polyploid nature of cpDNA and the requirement of P for cpRNA degradation by PNPase.
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PMID:Integration of chloroplast nucleic acid metabolism into the phosphate deprivation response in Chlamydomonas reinhardtii. 1735 Nov 18

A prominent enzyme in organellar RNA metabolism is the exoribonuclease polynucleotide phosphorylase (PNPase), whose reversible activity is governed by the nucleotide diphosphate-inorganic phosphate ratio. In Chlamydomonas reinhardtii, PNPase regulates chloroplast transcript accumulation in response to phosphorus (P) starvation, and PNPase expression is repressed by the response regulator PSR1 (for PHOSPHORUS STARVATION RESPONSE1) under these conditions. Here, we investigated the role of PNPase in the Arabidopsis (Arabidopsis thaliana) P deprivation response by comparing wild-type and pnp mutant plants with respect to their morphology, metabolite profiles, and transcriptomes. We found that P-deprived pnp mutants develop aborted clusters of lateral roots, which are characterized by decreased auxin responsiveness and cell division, and exhibit cell death at the root tips. Electron microscopy revealed that the collapse of root organelles is enhanced in the pnp mutant under P deprivation and occurred with low frequency under P-replete conditions. Global analyses of metabolites and transcripts were carried out to understand the molecular bases of these altered P deprivation responses. We found that the pnp mutant expresses some elements of the deprivation response even when grown on a full nutrient medium, including altered transcript accumulation, although its total and inorganic P contents are not reduced. The pnp mutation also confers P status-independent responses, including but not limited to stress responses. Taken together, our data support the hypothesis that the activity of the chloroplast PNPase is involved in plant acclimation to P availability and that it may help maintain an appropriate balance of P metabolites even under normal growth conditions.
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PMID:Abnormal physiological and molecular mutant phenotypes link chloroplast polynucleotide phosphorylase to the phosphorus deprivation response in Arabidopsis. 1971 Feb 29