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Query: EC:3.1.27.4 (ribonuclease)
 6,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The present paper describes intracellular changes in ribonuclease specific activity during Ca2+-induced sporangium formation in the water mold Achyla bisexualis. The enzymes undergo a decrease in activity prior to crosswall formation followed by an increase in activity during spore cleavage. As spore discharge occurs the RNase activity again decreases. A large percentage of the nuclease activity is associated with a lysosomal-like fraction of the cell, but there is also considerably activity associated with nuclear and microsomal fractions. Addition of cycloheximide or actinomycin D at various times during development prevents further decrease or increase in the enzyme activity. Mixing of cell extracts from different developmental stages provides evidence that inhibitors or activators of the enzyme activity are not responsible for the activity levels evident at the different stages. There is a change in the total levels of presumptive mRNA during Ca2+-induced sporangial formation which appears to be associated with the patterns of RNase activity. Utilizing total cellular RNA and Poly(A)+ RNA with the crude ribonuclease preparations, no substrate specificity could be ascertained.
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PMID:The development patterns of lysosomal enzyme activities during Ca2+-induced sporangium formation in Achyla bisexualis. III. Ribonucleases. 98 98

The synthesis of poly(A)-containing RNA by isolated mitochondria from Ehrlich ascites cells was studied. Isolated mitochondria incorporate [3H]AMP or [3H]UTP into an RNA species that adsorbs on oligo (dT)-cellulose columns or Millipore filters. Hydrolysis of the poly(A)-containing RNA with pancreatic and T1 ribonucleases released a poly(A) sequence that had an electrophoretic mobility slightly faster than 4SE. In comparison, ascites-cell cytosolic poly(A)-containing RNA had a poly(A) tail that had an electrophoretic mobility of about 7SE. Sensitivity of the incorporation of [3H]AMP into poly(A)-containing RNA to ethidium bromide and to atractyloside and lack of sensitivity to immobilized ribonuclease added to the mitochondria after incubation indicated that the site of incorporation was mitochondrial. The poly(A)-containing RNA sedimented with a peak of about 18S, with much material of higher s value. After denaturation at 70 degrees C for 5 min the poly(A)-containing RNA separated into two components of 12S and 16S on a 5-20% (w/v) sucrose density gradient at 4 degrees C, or at 4 degrees and 25 degrees C in the presence of formaldehyde. Poly(A)-containing RNA synthesized in the presence of ethidium bromide sedimented at 5-10S in a 15-33% (w/v) sucrose density gradient at 24 degrees C. The poly(A) tail of this RNA was smaller than that synthesized in the absence of ethidium bromide. The size of the poly(A)-containing RNA (approx. 1300 nucleotides) is about the length necessary for that of mRNA species for the products of mitochondrial protein synthesis observed by ourselves and others.
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PMID:The synthesis of polyadenylic acid-containing ribonucleic acid by isolated mitochondria from Ehrlich ascites cells. 98 39

Poly(A)-containing RNA was isolated by cellulose column chromatography from total RNA extracted from Chlorella fusca var. vacuolata 211/8p. RNA retained by the column was identified as poly(A)-containing RNA because it contained ribonuclease-resistant tracts, 25 to 55 nucleotides in length, from which not less than 80% of base was found to be adenine after acid hydrolysis. The base composition of poly(A)-containing RNA differed from that of RNA (largely ribosomal) which did not adsorb to cellulose, having a higher adenine content and a lower guanine content. Poly(A)-containing RNA was polydisperse including molecules with mobilities from 10S to 40S with a mean of about 20S. In an in vitro system derived from wheat-germ, protein synthesis was stimulated by adding poly(A)-containing RNA from Chlorella. Optimum conditions were established in this system with respect to the amount of poly(A)-containing RNA added and the concentration of KCl and Mg-2+. It is proposed that, in Chlorella, poly(A)-containing RNA includes cytoplasmic mRNA as has been shown for some other eucaryotic organisms.
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PMID:Characterization and messenger activity of poly(A)-containing RNA from Chlorella. 115 44

The human hepatic asialoglycoprotein receptor comprises two homologous polypeptides designated H1 and H2. Two distinct complementary DNA clones encoding these receptor subunits have been previously isolated from the human hepatoblastoma cell line HepG2. We discovered that multiple variants of H2 transcripts exist both in HepG2 cells and in the normal human liver that, at least in part, appear to be the result of alternative splicing events. We have found that (a) the complementary DNA clone for H2 previously isolated from HepG2 cells, characterized by a 57-nucleotide insertion within the 5' end of the complementary DNA that is absent from H1, represented only one third of H2-related sequences in an unamplified normal human liver complementary DNA library and less than 10% of H2 clones in HepG2 cells; (b) the predominant message for H2 expressed in the liver and HepG2 cells, designated L-H2, appeared to represent the fully processed product of the gene encoding both L-H2 and H2; and (c) a variant H2 transcript existed in HepG2 cells, designated H2', that contained a novel, 5' 88-bp nucleotide insertion. Poly(A+) RNA analysis of the normal liver and HepG2 cells by complementary RNA hybridization and ribonuclease protection corroborated the observations made during the screening of complementary DNA libraries regarding the abundance of the various messages. A striking incongruity was found between the levels of messenger RNA containing the H2-specific 57-nucleotide sequence and the levels of polypeptide expressed in the liver and HepG2 cells as recognized by antiserum specifically raised against this sequence.
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PMID:Differences in the abundance of variably spliced transcripts for the second asialoglycoprotein receptor polypeptide, H2, in normal and transformed human liver. 137 82

The eosinophil cationic protein (ECP), a potent helminthotoxin with considerable neurotoxic activity, was recently shown to also have ribonucleolytic activity. In this work the substrate preference of ECP ribonuclease action was studied in detail. With single-stranded RNA or synthetic polyribonucleotide substrates ECP showed significant but low activity, 70- to 200-fold less than that of bovine RNase A. ECP hydrolyzed RNA more rapidly than it did any synthetic polynucleotide. Poly(U) was degraded more rapidly than poly(C), and poly(A) and double-stranded substrates were extremely resistant. Defined low molecular weight substrates in the form of the 16 dinucleoside phosphates (NpN') and uridine and cytidine 2',3'-cyclic phosphates were tested, and none showed hydrolysis by ECP at a significant rate. The results link ECP ribonucleolytic activity to the 'non-secretory' liver-type enzymes rather than to the 'secretory' pancreatic-type RNases.
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PMID:Ribonuclease activity and substrate preference of human eosinophil cationic protein (ECP). 171 91

Poly(A)-specific ribonuclease was co-purified with poly(A) polymerase from Vigna unguiculata seedlings. Both activities were separated into two forms (enzymes I and II) by a final hydrophobic column chromatography. The enzyme I preparation, which was homogeneous as examined by SDS/PAGE, had both poly(A) polymerase and poly(A)-specific ribonuclease activities. The antibody raised to the enzyme I preparation precipitated both enzyme activities. These indicate that a single polypeptide (Mr 63,000) is responsible for both poly(A)-polymerizing and poly(A)-hydrolyzing activities. The poly(A)-specific ribonuclease was a 3'-exonuclease specific to single-stranded poly(A), forming 5'AMP as the sole reaction product. The hydrolytic activity required either Mn2+ or Mg2+ with different optimum concentrations, whereas the polymerizing activity required Mn2+ but not Mg2+. ATP and PPi had little or no effect on the poly(A)-specific ribonuclease activity.
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PMID:Poly(A) polymerase from Vigna unguiculata seedlings. A bifunctional enzyme responsible for both poly(A)-polymerizing and poly(A)-hydrolyzing activities. 255 12

The substrate specificity of a calcium-dependent endoribonuclease of Trypanosoma brucei cytoplasm has been further determined. The actions of the enzyme on transfer RNA, ribosomal RNA and various synthetic polyribonucleotides indicate that the enzyme degrades double-stranded as well as single-stranded RNAs; while it preferentially hydrolyses polyribonucleotides having adenylic acid residues, and has a pronounced preference for poly (adenylic acid). Its apparent Michaelis constant (Km) values using different substrates also suggest a base-preferential affinity of the enzyme to adenylate. The relative activity of the ribonuclease against homopolyribonucleotides is poly(A) greater than poly(U) greater than poly(C); while poly(G) is completely resistant to the activity. Poly(A) segments on poly(A)-rich RNA are selectively hydrolyzed by the endoribonuclease. A possible implication of this enzyme in the post-transcriptional modification and turnover of mRNA molecules is suggested.
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PMID:Calcium-dependent endoribonuclease of Trypanosoma brucei has a base-preferential affinity to adenylate. 258 76

Though the substantial part of serum ribonuclease (EC 3.1.27.5) is of pancreatic origin, there are no consistent data on changes in activity of serum alkaline ribonuclease in acute pancreatitis. The recent findings suggest that the increase in ribonuclease activity refers only to patients with necrotic outcome of acute pancreatitis. The aim of this study was to reevaluate the suggestion that elevated ribonuclease activity is specifically related to pancreatic necrosis. Our studies included 57 patients with verified acute pancreatitis, and 11 patients evolving haemorrhagic or necrotic lesions of the pancreas. It was found, that the enzyme increasing in some percentage of patients with acute pancreatitis is the Poly-C avid "pancreatic" ribonuclease. This enzyme begins to increase in the 2nd or third day after onset of the disease, always after decrease in serum amylase activity down to levels close to normal range. Ribonuclease activity increased up to days 5 or 6 of the disease, and then decreased along with diminution of disease symptoms upon treatment. Correlation studies showed that increased ribonuclease activity in acute pancreatitis is related to a higher than the 2nd degree of severity of the clinical course of the disease, to pancreatic necrosis, death, diminished glomerular filtration rate, and age. Thus, pancreatic necrosis is not the exclusive factor directing the increased ribonuclease activity in acute pancreatitis, but the increased ribonuclease activity seems to be a late marker of acute pancreatitis of a severe clinical course.
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PMID:Determination of ribonuclease activity in serum of patients with pancreatic necrosis. An attempt of extending the enzyme diagnosis of acute pancreatitis. 261 34

Yeast cells, Candida utilis, in water suspension and in the absence of electrolytes were found to be very sensitive to several proteins of moderate size, including ribonuclease, protamine, lysozyme, bovine serum albumin, cytochrome c, and myoglobin. Viability ceases rapidly, and ultraviolet-absorbing compounds (260 mmu) and the amino acid pool are released into the medium. The ultraviolet-absorbing material appears to be the nucleotide and coenzyme fraction usually extracted by 0.2 n perchloric acid at low temperature. The ribonucleic acid fraction remains in the cell ghosts and can be released by ribonuclease. The enzymatic properties of some of these proteins have no relation to their damaging effect on the cell membrane. Poly-l-lysine shows the same activity.
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PMID:Effect of some proteins on the yeast cell membrane. 429 20

Poly(U) binds to globin mRNA in 0.1m-NaCl. Studies with ribonuclease digestion of this complex suggest that there are polyadenylate-rich sequences in the mRNA containing about 30-40 adenylate residues. The sequences appear to be homogenous and of approximately the same length for both alpha- and beta-globin mRNA. They are most likely located at the 3' terminus of the molecule.
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PMID:Interaction between polyuridylic acid and rabbit globin messenger ribonucleic acid. 435 10


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