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PubMed1979

Specific inhibitors directed at the individual components of ribonucleotide reductase as an approach to combination chemotherapy.

It had been shown previously that the ribonucleotide reductase from mouse tumor consisted of two nonidentical components (Tris and dye fractions, each prepared from the 20 to 40% (NH/)2SO4 protein fraction containing the ribonucleotide reductase activity by blue dextran-Sepharose chromatography). The individual components either separated or present in the intact enzyme can be specifically and independently inhibited by different compounds. The Tris fraction component was inhibited by 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone while the dye fraction component was inactivated by pyridoxal phosphate:BH4- and the dialdehyde derivative of inosine (Inox) and 5'-deoxyinosine prepared by the periodate oxidation of inosine and 5'-deoxyinosine. The intact enzyme could be completely inhibited by any of these compounds. Reductase activity was restored by reconstitution with the exogenous components. The individual components of the reductase in the intact Ehrlich tumor cell could also be specifically inhibited. Activity in the crude cell-free extracts prepared from 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone- or Inox-treated cells was restored by the addition of the appropriate exogenous component. These data suggest that combinations of inhibitors of ribonucleotide reductase which specifically inhibit the components may be useful in the treatment of cancer.

Aldehydes↗
PubMed1978

Assay of ribonucleotide reduction in nucleotide-permeable hamster cells.

Ribonucleotide reduction was measured in Chinese hamster ovary cells made permeable to nucleotides by treatment with the detergent Tween-80. When compared to the respective ribonucleotide reductase activity in partially purified cell extracts, CDP and GDP reductase activities in permeabilized cells responded in a similar fashion to dithiothreitol, pH, MgCl2, FeCl3, substrate concentration and the presence of positive or negative allosteric effectors. At low protein concentrations both CDP and GDP reduction with whole cells increased linearly with cell number and was greater than the activity in corresponding cell extracts. Permeabilized cells were used to measure the level of CDP and GDP reductase in a hamster cell line resistant to the cytotoxic effects of hydroxyurea. The hydroxyurea-resistant cell line contained four to ten times more CDP and GDP reductase activity compared to parental or revertant cell lines. The permeabilized cell assay was also used to measure CDP and GDP reductase activities in Chinese hamster ovary cells synchronized by isoleucine starvation. CDP reductase activity was low in G1 arrested cells but increased 10-fold by 16 hours after the readdition of isoleucine to the growth medium. GDP reductase, which is present at much higher levels, is similarly induced after isoleucine addition, but only by 2-fold. The maximum activity of both CDP and GDP reductase occurred from 14 to 16 hours after isoleucine addition, which corresponded to the period of maximum DNA synthesis.

Animals↗
PubMed2026

Bacillus subtilis RNase HII Is Inefficient at Processing Guanosine Monophosphate and Damaged Ribonucleotides.

During one round of DNA replication, nearly 2000 ribonucleoside monophosphates (rNMPs) are incorporated in place of their cognate deoxyribonucleoside monophosphates (dNMPs). Given their high rate of insertion, genomic DNA could contain rNMPs that are damaged or mismatched. Here, we test the activity of Bacillus subtilis and Escherichia coli RNase HII on canonical, mismatched, and damaged rNMPs. We show that E. coli RNase HII is adept at incising most rNMP variants from DNA at similar frequencies, with the exception of an oxidized rNMP, where endoribonuclease activity is sharply reduced. In contrast, B. subtilis RNase HII efficiently incises rAMP, rCMP, and rUMP but is inefficient at processing rGMP in both a canonical and mismatched base pair. We test damaged ribonucleotides and find that B. subtilis RNase HII is refractory to processing abasic and oxidized ribonucleotide lesions. Our work shows that bacterial RNase HII enzymes have different intrinsic endoribonuclease activity toward the repair of canonical, mismatched, and damaged rNMPs, demonstrating that not all rNMP errors provoke efficient resolution. Our finding that B. subtilis RNase HII is recalcitrant to repairing damaged rNMPs resembles what is observed for eukaryotic RNase H2 orthologs, suggesting that other repair processes are necessary to resolve damaged rNMPs.

Bacillus subtilis↗
PubMed1977

Inhibition of mammalian ribonucleotide reductase by a dinucleotide produced in eucaryotic cells.

HS3, a highly phosphorylated dinucleoside originally purified from the fungus Achlya, has been isolated from Chinese hamster ovary cells undergoing glutamine starvation. The HS3 compounds obtained from the fungal and mammalian sources exhibited similar physical and chemical properties. This unusual dinucleotide may be an important regulator of eucaryotic ribonucleoside diphosphate reductase activity; for 50 micrometer HS3, isolated from either mammalian or fungal cells, significantly inhibited CDP reduction in Achlya or hamster cell preparations, but only marginally affected the activity of the enzyme from E. coli. Studies with HS3 isolated from Achlya and partially purified mammalian ribonucleotide reductase indicated that the compound noncompetitively inhibited the reduction of varying concentrations of the substrates CDP, ADP and GDP with Ki values of 23 micrometer, 14 micron and 16 micron respectively. These inhibitor concentrations are well below the estimated intracellular levels of HS3 in glutamine starved cells and suggest that HS3 inhibition of ribonucleotide reduction may be responsible for the rapid inhibition of DNA synthesis seen under these culture conditions.

Adenosine Diphosphate↗
PubMed1975

Long-term feeding study on disodium 5-ribonucleotide in dogs.

Groups of 4 male and 4 female Beagle dogs were fed for 2 years on diets containing 0 (control), 0.1, 1.0 and 2.0%, respectively, of disodium 5'-ribonucleotide (a 50 : 50 mixture of disodium 5'-inosinate and disodium 5'-guanylate). The mean daily intakes of the 3 test groups ranged during the experiment from 0.04-0.03, 0.48-0.26 and 0.93-0.51 g/kg, respectively. No effects attributable to treatment were found in mortality, food consumption, water consumption, bodyweight gain, ophthalmoscopy, clinical signs, haematology, serum chemistry (other than allantoin levels), organ weights, macroscopic pathology or histology, Small differences were observed between mean values in treatment and control dogs for serum allantoin but there was no indication of any persistent significant difference throughout the 2-year study. In a 6-week preliminary test, dietary levels of up to 10% disodium 5'-ribonucleotide were without detectable adverse effect upon beagle dogs of either sex.

Allantoin↗
PubMed1977

Ribonucleotide reductase from Escherichia coli. Identification of allosteric effector sites by chromatography on immobilized effectors.

Ribonucleotide reductase is responsible for the production of deoxyribonucleotides by catalyzing the reduction of ribonucleoside diphosphates. The enzyme is allosterically regulated in a complex way by the nucleoside triphosphates, ATP, dTTP, dGTP, dCTP, and dATP. Ribonucleotide reductase consists of two nonidentical subunits, proteins B1 and B2. Both substrates and allosteric effectors bind exclusively to B1. Binding of protein B1 to dTTP or dATP covalently coupled to Sepharose and elution with concentration gradients of the different nucleoside triphosphate effectors gave information about (1) the arrangement of the effector binding sites on protein B1 and (2) the affinity of the effectors for these sites. Protein B1 thus has two classes of effector binding sites. One class binds all effectors, as demonstrated by elution of the protein from dTTP-Sepharose with dATP, dGTP, ATP, or dCTP. The second class binds only dATP or ATP, since dATP and ATP were the only nucleotides which eluted protein B1 from dATP-Sepharose. These results confirm earlier data obtained by dialysis binding experiments. The eluting concentrations obtained for the different nucleoside triphosphates in experiments with dTTP-Sepharose could be used to calculate unknown dissociation constants for protein B1 -effector binary complexes. This was possible, since a plot of the eluting concentrations vs. known dissociation constants was linear.

Allosteric Site↗
PubMed1979

Isolation and characterization of purine-nucleoside phosphorylase-deficient T-lymphoma cells and secondary mutants with altered ribonucleotide reductase: genetic model for immunodeficiency disease.

The inherited deficiency of purine-nucleoside phosphorylase (PNPase; purine-nucleoside:orthophosphate ribosyltransferase, EC 2.4.2.1) in humans is associated with a severe deficiency of the T lymphocytes of the immune system. Because of the unsatisfactory nature of previously described model systems, we have selected, cloned, and characterized a mutant mouse T cell lymphoma (S49) completely deficient in PNPase. Of the four substrates of PNPase, only deoxyguanosine at low concentrations is toxic to the PNPase-deficient (NSU-1) cells. In order to delineate the biochemical processes necessary for the sensitivity of the NSU-1 cells to deoxyguanosine, we have isolated a series of secondary mutants resistant to deoxyguanosine from the PNPase-deficient line. One of these mutants is defective in its ability to transport deoxyguanosine into the cell. A second type of mutant cannot phosphorylate the deoxyguanosine and is totally deficient in deoxycytidine kinase activity. A third type of mutant (NSU-1-dGuo-L) can both transport and phosphorylate deoxyguanosine and accumulates dGTP. However, unlike its parent, NSU-1-dGuo-L does not become depleted of dCTP and TTP when exposed to exogenous deoxyguanosine. This observation is accounted for by the fact that the reduction of CDP to dCDP by the ribonucleotide reductase (ribonucleoside-diphosphate reductase, 2'-deoxyribonucleoside-diphosphate:oxidized-thioredoxin 2'-oxidoreductase, EC 1.17.4.1) of NSU-1-dGuo-L cells is not normally sensitive to feedback inhibition by dGTP.Thus, in order to exert its toxicity deoxyguanosine must be transported into the cell, be phosphorylated by deoxycytidine kinase, and be accumulated as dGTP. By inhibiting ribonucleotide reductase, dGTP depletes the cell of dCTP and to some extent TTP, thus preventing the synthesis of DNA, a process necessary for any proliferation-dependent function of T cells.

Animals↗
PubMed1976

Ribonucleotides in infectious bovine rhinotracheitis virus DNA.

Infectious bovine rhinotracheitis (IBR) virus was grown in the presence of 5-3H-uridine in a continuous line of bovine kidney cells. 5-3H-uridine was found to be associated with viral nucleocapsids. Furthermore, purification of the viral nucleic acid present in nucleocapsids illustrated that 5-3H-uridine was part of the viral nucleic acid. Purification of viral DNA from infected cells also indicated that 5-3H-uridine was associated with viral nucleic acid possibly as ribonucleotides. The label was identified as RNA by measuring its susceptibility to RNase and analysis of the bases. Short pulses with 5-3H-uridine, resulted in labelled nucleic acid which was extremely sensitive to RNase and alkali but resistant to DNase. Nucleotide analysis indicated that after short pulses all the radioactivity was associated with the base uracil whereas upon longer labelling periods a large percentage of the label was associated with cytosine. However even if viral DNA was isolated from nucleocapsids there was still some radioactivity associated with uracil. Sedimentation of heat denatured 5-3H-uridine label viral nucleic acid in CS2SO4 indicated that the label sedimented at a density of single stranded DNA suggesting that the ribonucleotides are covalently linked to the viral DNA.

Cell Line↗
PubMed1977

Ribonucleotide reductase from herpes simplex virus (types 1 and 2) infected and uninfected KB cells: properties of the partially purified enzymes.

Mammalian ribonucleotide reductase is a complex enzyme modified in its activity by a complex regulatory system involving adenosine triphosphate (ATP) and deoxyribonucleoside triphosphates. Infection of KB cells with herpes simplex virus (HSV) type 1 or 2 induces the formation of an altered ribonucleotide reductase. The properties of partially purified reductase from uninfected KB cells have been compared with the enzymes obtained from HSV-1 and HSV-2 infected KB cells. We found that the virus-induced enzymes are similar to the KB enzyme in some properties but differed significantly from the host enzyme in three respects: (1) virus induced reductase was not inhibited significantly by deoxythymidine triphosphate regardless of ATP concentration, (2) magnesium was not required for virus enzyme activity although 2 mM-Mg2+ did stimulate the reaction, and (3) magnesium concentration required for optimal activity was different for virus and host enzymes. These changes are evidence that the enzyme molecules present after infection by HSV-1 or HSV-2 differ from those present before infection.

Adenosine Triphosphate↗
PubMed2025

Bacillus subtilis RNase HII is inefficient at processing guanosine monophosphate and damaged ribonucleotides.

During one round of DNA replication, nearly 2,000 ribonucleoside monophosphates (rNMPs) are incorporated in place of their cognate deoxyribonucleoside monophosphate (dNMP). Given their high rate of insertion, genomic DNA would contain rNMPs that are damaged or mismatched. Here, we tested the activity of Bacillus subtilis and Escherichia coli RNase HII on all four canonical, mismatched, and damaged rNMPs. We show that E. coli RNase HII is adept at incising most rNMP variants from DNA at similar frequencies, with the exception of an oxidized rNMP, where endoribonuclease activity is sharply reduced. In contrast, B. subtilis RNase HII efficiently incised rAMP, rCMP, and rUMP, but was inefficient at processing rGMP in both a canonical and mismatched base pair. We tested damaged ribonucleotides and found that B. subtilis RNase HII is refractory to processing abasic and oxidized ribonucleotide lesions. Our work shows that bacterial RNase HII enzymes have different intrinsic endoribonuclease activity toward the repair of canonical, mismatched, and damaged rNMPs, demonstrating that not all rNMP errors provoke efficient resolution. Our finding that B. subtilis RNase HII is recalcitrant to repairing damaged rNMPs resembles what is observed for eukaryotic RNase H2 orthologs, suggesting that other repair processes are necessary to resolve damaged rNMPs.

Bacillus subtilis↗
PubMed1977

Drug uptake and ribonucleotide profiles of blast-enriched and blast-depleted human bone marrow cell populations.

A density cut method was used to prepare two subpopulations of bone marrow cells which were enriched (BE) and depleted (BD) respectively of blast cells. Marrow aspirates were obtained from 32 patients, 26 of whom had acute leukaemia. The uptake of a variety of chemotherapeutic agents by these two subpopulations and the acid-soluble ribonucleotide profiles of the populations were compared and significant differences were found in drug uptake by BE and BD subpopulations. For some drugs such as cytosine arabinoside, uptake was greatest by the BE cells, while for 5-azacytidine the BD subpopulation took up the greatest amount of the drug. The preparation of the BE subpopulation also permitted the recognition of several patients with acute leukaemia whose blast cells possess nondetectable levels of ATP, UTP, and GTP components in their acid-soluble fractions. The studies presented demonstrate the necessity of using purified cell populations when characterizing the drug uptake patterns and the soluble ribonucleotide profiles of the leukaemic cells. A simple method for enriching bone marrow aspirates for leukaemic cells is also presented.

Antimetabolites↗
PubMed1976

Ribonucleotide reductase in blue-green algae: dependence on adenosylcobalamin.

Ten species of freshwater blue-green algae exhibit an adenosylcobalamin-dependent ribonucleotide reductase, thuse explaining the requirement for cobalt by these organisms. The evidence suggests a phylogenetic affinity between the cyanophytes and bacteria, such as Clostridium and Rhizobium, and the euglenoid flagellates, which also use the cofactor-dependent reductase. In contrast, the ribonucleotide reductase reaction in the few green algae surveyed shows no dependence on cobalamins.

Biological Evolution↗
PubMed1977

Microbial transformation of antibiotics. Clindamycin ribonucleotides.

Addition of clindamycin to whole-cell cultures of Streptomyces coelicolor Müller resulted in the loss of in vitro activity against organisms sensitive to clindamycin. Incubation of such culture filtrates with crude alkaline phosphatase generated a biologically active material identified as clindamycin. Fermentation broths containing inactivated clindamycin yielded clindamycin 3-ribonucleotides and clindamycin 3-phosphate the structure of which was established by physicochemical and enzymatic means. Attempts to transform clindamycin to clindamycin 3-ribonucleotides by lysates or partially purified enzyme preparations from S. coelicolor have failed.

Animals↗
PubMed1976

[Mitochondrial thymidine kinase and ribonucleotide reductase from rat liver and rat hepatoma 27].

Fractions of heavy and light mitochondria are isolated from homogenates of homologous rat tissues (intact liver, regenerating liver within 24 hours after hepatectomy and 27 hepatoma) by means of differential centrifugation. It is found that tumour mitochondria have higher heterogeneity and lower buyoant density than mitochondria from normal hepatocytes. The activity of two enzymes of DNA precursors synthesis (ribonucleotide reductase and thymidine kinase) in subcellular fractions is demonstrated to correlate with the tissue growth rate. A single injection of cyclic AMP into hepatectomised rats resulted in the retardation of the regeneration process, and the activity of both enzymes reached its normal level in all the fractions studied after 24 hours after the operation. Thymidine kinase and ribonucleotide reductase are located mainly in the mitochondrial matrix, however, pronounced enzyme activity is observed also in membrane fractions. The activity of the enzymes in the fraction of external mitochondria membranes in rapidly growing tissues is 2--3 times as high as in the same fraction from normal rat liver.

Animals↗
PubMed1978

Differential effect of hydroxyurea on a ribonucleotide reductase system.

Infection of Escherichia coli with phage T4 induces a large increase in ribonucleotide reductase activity. We show that hydroxyurea inhibits T4-induced CDP, ADP, UDP, and GDP reductase activities in vitro. Moreover, there are significant differences in the degree of inhibition of each ribonucleotide reductase activity. The reductase activities for CDP and ADP are more sensitive to hydroxyurea than those for UDP and GDP, particularly at high hydroxyurea molarities. As little as 5 x 10(-4)M hydroxyurea lowers CDP and ADP reductase activities to 25 to 30% whereas as much as 0.5 M hydroxyurea is needed to lower UDP and GDP reductase activities to 50%.

Coliphages↗
PubMed1978

Reconstitution of the ribonucleotide reductase enzyme from Ehrlich tumor cells.

Ribonucleotide reductase from Ehrlich tumor cells was separated by chromatography on blue dextran/Sepharose into two protein fractions (Tris and Dye fractions). Neither fraction alone had reductase activity, but when combined, constituted an active enzyme system. Heat treatment of either fraction resulted in an inactive combination. The approximate molecular size of the active component of the Tris and Dye fractions was determined to be 5.7 S and 6.5 S, respectively, compared to 9 S for the intact enzyme. The Tris fraction was inactivated by hydroxylamine while the dye fraction was inactivated by pyridoxal phosphate/BH4-treatment. The inactivation of the Dye fraction was prevented by ATP. These data would indicate that the Tris and Dye fractions were comparable in function to the B2 and B1 proteins, respectively, of the Escherichia coli ribonucleotide reductase.

Animals↗
PubMed1977

[Correlation of mitochondrial ribonucleotide reductase and thymidine kinase activities with the synthesis of mitochondrial DNA in rat liver during regeneration].

3H-thymidine incorporation into DNA of heavy mitochondria from regenerating rat liver and the change of mitochondrial thymidine kinase and ribonucleotide reductase activities are studied in vivo in regenerating rat liver within 6--48 hours after hepatectomy. Synthesis of mitochondrial DNA and changes in the activity of the enzymes studied are found to be undulate. Thymidine kinase activity maxima coincide with those of 3H-thymidine incorporation. Maximal activity of ribonucleotide reductase pre-exists maxima of mitochondrial DNA synthesis.

Animals↗
PubMed1978

[Comparison of free ribonucleotide pool in the spleens of C57BL and DBA/2 mice and in leukemia cells sensitive and resistant to 5-fluorouracil].

The amount of free purine and pyrimidine ribonucleotides in the spleens of mice (C57Bl and DBA/2) and in lympholeukemia cells (La and L1210), sensitive and with induced resistance to 5-fluorouracil, was determined by chromatography on a column with DEAE-cellulose. It was found that the cytidine ribonucleotide pool in the spleens of DBA/2 mice is 2 times lower as compared to C57Bl mice. The lympholeukemia cells (La and L1210) isolated from the animals also differed in their uridine nucleotide pools. The development of leukemia was accompanied by a decrease in ATP and GTP. No significant changes in the total amount of pyrimidine nucleotides under developing resistance to 5-fluororuacil were observed.

Animals↗