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

The reaction of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole [NBD-Cl] with purified eel electrophax Na+ and K+ stimulated adenosine triphosphatase [(Na-K)ATPase] has been monitored by changes in the (Na-K)ATPase activity, the K+ stimulated p-nitrophenyl phosphatase [PNPase] activity, and the protein ultraviolet absorption spectrum. The NBD-Cl reacts with two tyrosine residues per mol of enzyme (approximately 6-7 nmol/mg of protein), as judged by changes in protein absorption spectra and incorporation of [14C]NBD-Cl. The modified tyrosine groups are located on the Mr = 95 000 polypeptide chain and react at different rates. Only one tyrosine modification is necessary for complete inhibition of (Na-K)ATPase activity, although both must be modified for complete inhibition of PNPase activity. Reversal of these modifications by 2-mercaptoethanol restores 65% of both activities. Na+ increases the rate of tyrosine modification, K+ decreases the rate, and ATP affords the more reactive tyrosine group complete protection. NBD-Cl modification of approximately 6-7 nmol of tyrosine groups/mg of protein results in a large decrease in ATP affinity as judged by equilibrium binding. These results are compared with similar results obtained from NBD-Cl modification of the coupling factors of oxidative phosphorylation and photophosphorylation. A model is presented suggesting an asymmetric arrangement of two 95 000 polypeptide chains with a single tyrosine residue at the ATP site.
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PMID:Reaction of (Na-K)ATPase with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole: evidence for an essential tyrosine at the active site. 14 73

We have used an in vitro Escherichia coli tRNA processing system to investigate the specific role of individual exoribonucleases in the 3' maturation of tRNA precursors. The processing of pre-tRNA(Tyr)su3+ and pre-tRNA(2Arg) was studied using extracts from cells lacking one or multiple exoribonucleases or using purified RNases. Earlier genetic studies had suggested that multiple exoribonucleases contributed to the maturation of tRNA precursors, and this was proven directly in the studies described here. Complete 3' processing required the combined action of multiple exoribonucleases, and each RNase showed distinct specificities for maturation of the different parts of the 3' precursor segment. RNase II and polynucleotide phosphorylase were most effective in shortening long 3' trailer sequences to intermediates with 2-4 extra 3' residues. Final trimming of the last few 3' nucleotides of these precursors was carried out most efficiently by RNases T and PH, but the two enzymes differed in their specificity for individual nucleotide positions. Depending on the tRNA precursor, the relative importance of the various RNases to the overall maturation process differed. We also showed that purified exoribonucleases can completely complement mutant extracts and that tRNA maturation can be totally reconstructed in vitro using purified enzymes. These studies provide the first detailed information about the specific role of individual exoribonucleases in tRNA processing, and bring us closer to defining a complete E. coli tRNA maturation pathway.
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PMID:The role of individual exoribonucleases in processing at the 3' end of Escherichia coli tRNA precursors. 750 97

The platelet population of man and rat can be divided into two classes of about equal size on the basis of presence/absence of an acid phosphatase which acts on para-nitrophenylphosphate (a PNPase), at pH 5. The cytochemical reaction product is in the platelet cytoplasmic matrix, without apparent association with organelles or membrane systems. We could not relate differences in staining to differences in function: all cells responded the same to activation by thrombin, ADP, or collagen, in fibrinogen binding to activated platelets, by endocytosis of fluid-phase tracers, and in internalization of latex particles. With respect to possible physiological substrates for the PNP-ase, there was no reaction product from beta-glycerophosphate, AMP, ADP, ATP, GTP, CMP, IMP, cAMP, creatine phosphate, and inositol phosphates, and the enzyme was not inhibited by 40 mM lithium. There was reaction product from tyrosine phosphate suggesting that the physiological substrate for PNP-ase is tyrosine phosphate. In rat bone marrow, megakaryocytes also were of two classes, PNPase positive and PNPase negative, suggesting that different classes of platelets arise from different classes of megakaryocytes.
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PMID:Blood platelet heterogeneity: evidence for two classes of platelets in man and rat. 752 21