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[Mechanism of the enzymatic reaction catalyzed by uridine diphosphate glucose dehydrogenase. The chemical synthesis of uridine diphosphate glucose-6-H3 and its oxidation by uridine diphosphate glucose dehydrogenase].

The synthesis of UDP-glucose-6-s-H was performed through condensation of alpha-D-glucopyranosyl phosphate-6-3-H and uridine 5'-phosphomorpholidate. Enzymic oxidation of UDP-glucose-6-3-H with calf liver UDP-glucose dehydrogenase was found to proceed with direct transfer of the hydrogen from C-6 of UDP-glucose onto NAD.

Alcohol Oxidoreductases↗
PubMed1975

Analysis of uridine incorporation in chicken embryo cells infected by vesicular stomatitis virus and its temperature-sensitive mutants: uridine transport.

The shut-off of RNA synthesis in chicken embryo cells, after infection with vesicular stomatitis virus, is partially due to a reduced capacity of the infected cells to transport uridine. Permeability to uridine decreases exponentially after infection. This loss of ability to transport uridine may be caused either by structural components of the input virions or may result from the expression of the viral gene products. In the latter case, only minor levels of viral transcription is sufficient to modify cellular permeability, since, even at low multiplicities, RNA minus temperature-sensitive (ts) mutants of vesicular stomatitis virus bring about a significant diminution of uridine incorporation in cells infected under nonpermissive conditions. Experiments with mutants of group III suggest that the M protein of the viral envelope may play a role in the sequence of events that modifies uridine transport. In addition to this cause of the diminution of incorporation of uridine by infected cells, another mechanism is noted which requires protein synthesis.

Animals↗
PubMed1979

Effect of diabetes and fasting on the uridine triphosphate content and uridine kinase activity of rat cardiac and skeletal muscle.

The influence of diabetes and starvation on uracil nucleotide metabolism in muscle was studied. It was found that the uridine triphosphate (UTP) content of heart and diaphragm muscle was decreased in fasted and streptozotocin-diabetic rats and that insulin treatment of diabetic animals restored the UTP concentration to normal levels. The ATP content of heart tissue was not altered under these conditions. It was also demonstrated that hemidiaphragms from streptozotocin-diabetic rats synthesized less UTP from uridine in vitro than hemidiaphragms from normal animals. Uridine kinase activity of extracts of cardiac and skeletal muscle from fasted and diabetic rats was lower than the activity found in extracts from control animals. It was concluded that uracil nucleotide synthesis by the salvage pathway is decreased in experimental diabetes and fasting.

Animals↗
PubMed1977

Uridine-cytidine kinase. III. Competition between uridine and cytidine for a single enzyme.

The combined phosphorylation of uridine and cytidine by a partially purified preparation of uridine-cytidine kinase has been studied with dual-substrate kinetics. The kinetic patterns obtained are consistent with the theoretical analysis for two competing, alternate substrates interacting with a single enzyme. Thus, despite feedback regulation of the kinase by both UTP and CTP, the results allow a clear conclusion that both nucleosides are phosphorylated by the same enzyme, and probably at a single site, rather than by two closely related isozymes, each specific for one pyrimidine.

Allosteric Regulation↗
PubMed1975

Interaction of uridine diphosphate glucose with calf liver uridine diphosphate glucose dehydrogenase. Significance of hydroxyl groups at C-3, C-4 and C-6 of hexosyl residue.

Analogs of uridine diphosphate glucose (UDPGlc) with a modified hexosyl residue which contained a deoxy-unit at C-3 or C-4 were tested as substrates of calf liver UDPGlc dehydrogenase (EC 1.1.1.22). The 3-deoxyglucose derivative was found not to serve as a substrate for the enzyme whereas the 4-deoxyglucose analog was able to participate in the reaction. The apparent Km of the latter was 5.3 times that of UDPGlc and the relative V was 0.04. The reaction product was identified as uridine diphosphate deoxyhexuronic acid. UDP-deoxyhexoses were non-competitive inhibitors of UDPGlc enzymic oxidation, inhibition increased in the sequence: 2-deoxy-less than 3-and 6-deoxy-less than 4-deoxyglucose derivative. The significance of different HO-groups in hexosyl residue for interaction of UDPGlc with the enzyme is discussed.

Alcohol Oxidoreductases↗
PubMed1975

Interaction of uridine diphosphate glucose analogs with calf liver uridine diphosphate glucose dehydrogenase. Influence of substituents at C-5 of pyrimidine nucleus.

The interaction of alpha-D-glucopyranosyl pyrophosphates of 5-X-uridines (X = CH3, NH2, CH3O, I, Br, Cl, OH) with uridine diphosphate glucose (UDPGlc) dehydrogenase (EC 1.1.1.22) from calf liver has been studied. All the derivatives investigated were able to serve as substrates for the enzyme. The apparent Michaelis constants for UDPGlc-analogs were dependent both on electronic and steric factors. Increase of substituent negative inductive effect lead to decrease of pKa for ionization of the NH-group in the uracil nucleus and, consequently, to a diminishing of the proportion of the active analog species under the conditions of assay. After correction for the ionization effect, the Km values were found to depend on the van der Waals radius of the substituent. The value of 1.95 A seems to be critical, as the analogs with bulkier substituents at C-5 showed a decreased affinity to the enzyme. The maximal velocity values of the analogs were also dependent on nature of the substituent. Good linear correlation between log V and substituent hydrophobic phi-constant was observed for a number of the analogs, although V values for the nucleotides with X = H, OH or NH2 were higher than would be expected on the basis of the correlation. The significance of the results for understanding of the topography of UDPGlc dehydrogenase active site is discussed.

Alcohol Oxidoreductases↗
PubMed1977

The reduction of uridine 5'-diphosphate and uridine 5'-triphosphate in some transplantable rat hepatomas.

The reduction of uridine 5'-diphosphate (UDP) and uridine 5'-triphosphate (UTP) has been studied in normal adult rat liver, the Dunning hepatoma, and Morris 5123D and 7793 hepatomas. A new paper chromatographic method that separates and quantitates all the major products of the reduction and hydrolysis or other reactions of the substrate has been devised. All of the above tissues were able to reduce UDP and UTP at relatively slow rates ranging from 0.25 nmole of deoxycompound formed (deoxyuridine 5'-triphosphate) per mg protein per hr for liver to 3.5 nmoles deoxyuridine 5'-triphosphate for the Morris 7793 hepatoma when UTP was the substrate. In general, UTP was a better substrate than UDP. The method may also be used to measure cytidine 5'-diphosphate (CDP) reduction, and under the same conditions, the reduction of CDP proceeded at about 6 times the rate of UTP reduction in the Dunning hepatoma. Like CDP reduction, the reduction of UTP was strongly modulated by ATP. Reduction of UTP was insignificant with no ATP or 1.5 micronmoles ATP added to the reaction mixture and was maximal with 0.25 micronmole. The reduction of UTP was inhibited by deoxyuridine 5'-monophosphate, deoxythymidine 5'-triphosphate, deoxycytidine 5'-triphosphate, and deoxyribose 1'-phosphate. The effects of deoxyadenosine 5'-triphosphate varied, depending on its concentration in the reaction medium and whether UDP or UTP was a substrate. However, hydroxyurea did not inhibit reduction of UDP or UTP at concentrations that strongly inhibited CPD reduction. All of the tissues were able to hydrolyze [alpha-32P]deoxyuridine 5'-triphosphate readily to the diphosphate and monophosphate. It is suggested that the enzyme that reduces UTP or UDP may be different in these tissues from the enzyme that reduces CDP.

Animals↗
PubMed1978

Reduced hepatic bilirubin uridine diphosphate glucuronyl transferase and uridine diphosphate glucose dehydrogenase activity in the human fetus.

Hepatic bilirubin uridine diphosphate glucuronyl transferase (UDPG-T) activity was 0.14 and 0.22 units in two fetuses aged 17 and 22 weeks, respectively, and less than 0.1 unit in 15 fetuses, aged 8--19 weeks compared to 0.68--1.99 units in 21 normal adults. Hepatic uridine diphosphate glucose dehydrogenase (UDPG-D) activity in 14 fetuses, aged 8--18 weeks, ranged from 6.2--15.0 units (mean = 11.3 +/- 0.7) compared to 28.8--49.2 units (mean = 39.6 +/- 2.5) in eight normal adults (P less than 0.001). There was no correlation between UDPG-D activity and gestational age. The hepatic UDPG-D activity was 16.5 units in a 33-day-old full term, female infant, 42.4 and 24.3 units in two 2-year-old infants, respectively, and 24.3 units in a 5.5-year-old child. In three human fetuses, the apparent Km UDPG was 0.54 x 10(-4) M. Thus, both hepatic bilirubin UDPG-T and UDPG-D activity are markedly reduced in the human fetus during the second trimester of gestation. Retarded development of hepatic UDPG-D may extend beyond the first month of life.

Adult↗
PubMed1992

The L protein of vesicular stomatitis virus transcription complexes is specifically photolabelled by 5-azido-uridine 5'-triphosphate, an analogue of the RNA polymerase substrate uridine 5'-triphosphate.

A photoactive nucleotide analogue of UTP, 5-azido-uridine 5'-triphosphate (5-N3UTP), has been demonstrated to interact with the RNA polymerase of the vesicular stomatitis virus (VSV) transcription complex. Kinetic studies indicated that 5-N3UTP served as an efficient replacement for UTP in in vitro polymerase reactions. The Km for the azido analogue was 27 microM and that of the natural substrate, UTP, was 7 microM. Photolysis of [gamma-32P]5-N3UTP in the presence of VSV transcription complexes resulted in selective radio-labelling of the L protein. This photolabelling was saturable with an apparent Kd of 28 microM. The L protein was protected from [gamma-32P]5-N3UTP-mediated photolabelling by competing natural substrates (UTP, CTP, ATP, GTP). The stoichiometry of photoprobe incorporation into the transcription complex was close to unity with respect to the L protein. These data provide evidence that the nucleotide-binding domain of the VSV RNA polymerase contains amino acid residues of the L protein.

Affinity Labels↗
PubMed1979

[Comparison of reactivities or uridine- and cytidine-2',3'-cyclophosphates as donors and uridine and cytidine as acceptors of phosphate under dinucleoside monophosphate synthesis catalyzed by RNAase A].

In order to determine the relative activity of pyrimidine nucleoside-2',3'-cyclophosphates as donors and nucleosides as acceptors of phosphate in the reaction of the internucleotide bond formation catalyzed by RNAase A (EC 3.4.1.22), a comparative synthesis of dinucleoside monophosphates UpU, UpC, CpU and CpC at three different enzyme concentrations (20, 40 and 70 mkg/ml) and two temperatures (0 degrees and -15 degrees) was carried out. The conversion rate of donor (U greater than p and C greater than p) during the synthesis and in the competitive reaction of hydrolysis strongly depends on the type of acceptor activity as compared to uridine. Based on the data of synthesis and simultaneous hydrolysis of U greater than p and C greater than p it may be concluded that in the both cases the latter donor is more reactive. The approaches to the determination of the substrate activity of the donors and acceptors for the evaluation of optimal conditions of the dinucleoside monophosphate synthesis depending on the donor--acceptor combination are discussed.

Cytidine↗
PubMed1975

Uridine diphosphate galactose-4-epimerase. Uridine monophosphate-dependent reduction by alpha- and beta-D-glucose.

Rates of UMP-dependent reduction of the DPN+ associated with Escherichia coli UDP-galactose-4-epimerase at 27 degrees and 0.2 M ionic strength in 0.1 M Tris-HCl buffer, pH 8.5, are reported. The reaction exhibits excellent pseudo-first order behavior when D-glucose is at anomeric equilibrium. The effects of [UMP] and [glucose] on the observed first order rate constants are consistent with the following equation. The symbols phi are empirical parameters. (See article). The data indicate that the pathway involves random equilibrium binding of UMP and glucose followed by rate-limiting decomposition of the ternary complex to epimerase-DNPH. The binding parameters indicate that the principal activating effect of UMP is not simply to increase the affinity of the enzyme for glucose. UMP appears to increase the reactivity or availability of enzyme-bound DPN+. The kinetic isotope effect for the reaction of D-]1-2H]glucose (kH/kD) is 4.2, which confirms that C-1 is oxidized and that hydride transfer is rate limiting. Both of the purified anomers, alpha- and beta-D-glucose, reduce the enzyme-bound DPN+. As indicated by the deviations from pseudo-first order kinetics because of concurrent mutarotation, the beta anomer is the more reactive, reacting about 4 to 5 times faster than the alpha anomer at concentrations well below saturation. Is is suggested that the lack of stereo-specificity in this reaction may be attributed to the two anomers being productively bound with their opposite faces projecting toward C-4 of bound DPN+. Nonstereospecific oxidation of alpha- and beta-D-glucose may be a model for the mechanism of UDP-hexose epimerization, which also involves nonstereospecific hydride transfer.

Arabinose↗