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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)

Specific activity and level of polynucleotide phosphorylase (PNPase) in polyribosomes of regenerating liver of adult rats, liver of newborn rats and in malignant tumours of rat (sarcoma M-1 and hepatoma 27) were studied. 24 hours after partial hepatectomy the specific activity and level of PNPase in regenerating liver decreased 3--4 times in the fraction of polyribosomes, bound to the endoplasmic reticulum membranes, and remained at a constantly low level in the fraction of free polyribosomes. The PNPase activity also showed a sharp decrease in the fraction of membrane-bound polyribosomes from newborn rats liver and could not be detected either in free or in bound polyribosomes from sarcoma M-1 or hepatoma 27. The PNPase activity in the fraction of bound polyribosomes increased with a decrease in the rate of liver growth (regenerating liver and newborn rats liver), and reached the level normal for adult animals. Possible mechanisms of regulation of the PNPase activity in animal tissue were studied. It was found that a 2-fold administration of cyclic 3,5'-AMP to intact animals (5 mg per 100 g of body weight) with an interval of 8 hours, corresponding to the interval between two peaks of the increase in cyclic 3,5'-AMP concentration following partial hepatectomy, diminished the PNPase specific activity in polyribosomes by 30%. A factor, presumably of protein origin, which induced a release of PNPase from polyribosomes of normal rat liver but did not affect the activity of the liberated enzyme, was detected in the cell sap of sarcoma M-1 and hepatoma 27.
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PMID:[The activity of polynucleotide phosphorylase in polyribosomes of regenerating liver of adult rats, liver of newborn rats and in some reinoculated tumours]. 19 Nov 6

Localization, physico-chemical and catalytic properties and possible biological functions of polynucleotide phosphorylase (PNPase) from animal tissues are discussed. In animal tissue cells PNPase has multiple localization; the major amount of the enzyme is localized in the endoplasmic reticulum ribosomes. In the nuclei PNPase, similar to other endo- and exo-RNAses participates in the processing of precursor molecules of mature forms of RNA, whereas in the cytoplasm it is involved in the destruction of polyribosomes in the polyribosomes of rapidly growing tissues the activity of PNPase is extremely decreased. The mechanisms regulating the PNPase activity in rapidly growing tissues are discussed.
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PMID:[Animal tissue polynucleotide phosphorylase]. 35 Feb 93

The type of RNA is studied, which is degraded by polynucleotide phosphorylase (PNPase) in the fraction of free ribosomes and ribosomes released from endoplasmic reticulum membranes with Triton X-100. Beta-32P labelled ADP, UDP, GDP and CDP are found among the degradation products of endogenous RNA of free and bound ribosomes in vitro in the presence of 32P-ortophosphate. An analysis of molar ratio of beta-32P-NDP isolated revealed that PNPase degrades RNA of GC type in both ribosome fractions. The amount of PNPase-degraded RNA in bound ribosimes is 4-fold as high as that in free ribosomes under the same conditions. Analysis of stable 32P-RNA and rapidly labelled 32-P-dRNA, isolated from bound ribosomes after the incubation with and without inorganic phosphate, revealed that PNPase attacks the 28S fragment of RNA, which consists of about 370 nucleotides, and dRNA having a sedimentation coefficient less than 12S. The rate of dRNA degradation is considerably higher than that of rRNA. 5'-RNAase, hydrolysing synthetic homopolyribonucleotides to oligonucleotides with free 3'-OH terminal group, apparently participates, together with PNPase, in dRNA and rRNA degradation.
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PMID:Study of the type of RNA, degraded by polynucleotide phosphorylase in polyribosomal fraction of rat liver. 121 63