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PubMed1976

Raman pH profiles for nucleic acid constituents I. Cytidine and uridine ribonucleosides.

Raman spectra of aqueous solutions of uridine and cytidine have been recorded as a function of pH with the band intensities and vibrational frequencies monitored to determine bands which may be considered as diagnostic of the concentration of the various species. Quantitative band intensity measurements indicate that not all pH-sensitive bands can be considered as diagnostic of the pK value for the acid form of the nucleoside, and for the percent species in solution. Although the accuracy of the Raman band intensity method is inherently less than that of the titrimetric or visible-ultraviolet spectrophotometric methods, the pK values and percent species agree well with those obtained from these methods. The utility of the results obtained from the pH profiles for cytidine is discussed in terms of the effect of acidification on the structural and conformational characteristics of polycytidylic acid in solution.

Cytidine↗
PubMed1978

Studies on the binding of adenylyl-3', 5'-cytidine to ribonuclease.

The interaction of adenylyl-3',5'-cytidine (ApC) with ribonuclease-A (RNAase-A) was studied by steady-state kinetics and ultraviolet difference spectroscopy. X-ray difference Fourier synthesis at 4 A resolution was also used to study the binding of ApC to RNAase-S. Unlike well-studied compounds like uridylyl-3',5'-adenosine, ApC binds in an unique way: (1) the cytidine moiety is bound to the B1 and R1 sites, (2) the adenosine moiety protrudes to the solution and is not fixed spatially and (3) the phosphate group is bound to the non-specific site (the "Po site") previously postulated (Sawada, F. and Irie, M. (1969) J. Biochem. (Tokyo) 66, 415--418) as the binding site for the 5'-phosphate of uridine 2',5'-diphosphate or uridine 3',5'-diphosphate. This conclusion is consistent with that derived for adenylyl-3',5' -4-thiouridine based on CD difference spectroscopy (White, M.D., Keren-Zur, M. and Lapidot, Y. (1977) Nucleic Acid Res. 4, 843--851). The "Po site" is most likely the epsilon-amino group of Lys 66.

Adenine Nucleotides↗
PubMed1976

Membrane-associated phosphatidylglycerophosphate synthetase from Escherichia coli: purification by substrate affinity chromatography on cytidine 5'-diphospho-1,2-diacyl-sn-glycerol sepharose.

The membrane-associated cytidine 5'-diphospho-1,2-diacyl-sn-glycerol (CDP-diglyceride):sn-glycerol-3-phosphate phosphatidyltransferase (EC 2.7.8.5) from Escherichia coli has been solubilized wiTriton X-100 and purified 6000-fold to 85% of homogeneity. The major purification was attained using several modifications of the the CDP-diglyceride Sepharose affinity chromatography system described by Larson et al. (Larson, T.J., Hirabayashi, T., and Dowhan, W. (1976), Biochemistry 15, 974). The native enzyme in Triton X-100 had an apparent molecular weight of over 200 000, as judged by Sepharose 6B gel filtration. The apparent size of the native enzyme appeared to be due to its association with Triton X-100, as judged by sucrose gradient centrifugation, polyacrylamide gel electrophoresis, and the lack of affinity for ion-exchange resins. The minimum subunit molecular weight of the enzyme, determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, was 24 000. This low molecular weight is consistent with the stability of enzyme to heat, urea, or sodium dodecyl sulfate denaturation. The purified enzyme had an absolute requirement for magnesium ion (KM = 50 mM) and Triton X-100 (0.5-6%) for activity when either CDP-diglyceride or dCDP-diglyceride was used as substrate. Kinetic analysis of the enzymatic reaction indicated an ordered sequential Bi-Bi reaction with the liponucleotide forming a dead-end complex at high concentration, which inhibited both the forward and reverse reactions. The enzyme would not hydrolyze the pyrophosphate bond of its lipid substrate or the phosphate esters of its lipid product but would catalyze a cytidine 5'-monophosphate dependent exchange reaction between glycero-3-phosphate and phosphatidylglycerophosphate.

Chromatography, Affinity↗
PubMed2024

Epitranscriptomic cytidine methylation of the hepatitis B viral RNA is essential for viral reverse transcription and particle production.

Epitranscriptomic RNA modifications have emerged as important regulators of the fate and function of viral RNAs. One prominent modification, the cytidine methylation 5-methylcytidine (m5C), is found on the RNA of HIV-1, where m5C enhances the translation of HIV-1 RNA. However, whether m5C functionally enhances the RNA of other pathogenic viruses remains elusive. Here, we surveyed a panel of commonly found RNA modifications on the RNA of hepatitis B virus (HBV) and found that HBV RNA is enriched with m5C as well as ten other modifications, at stoichiometries much higher than host messenger RNA (mRNA). Intriguingly, m5C is mostly found on the epsilon hairpin, an RNA element required for viral RNA encapsidation and reverse transcription, with these m5C mainly deposited by the cellular methyltransferase NSUN2. Loss of m5C from HBV RNA due to NSUN2 depletion resulted in a partial decrease in viral core protein (HBc) production, accompanied by a near-complete loss of the reverse transcribed viral DNA. Similarly, mutations introduced to remove the methylated cytidines resulted in a loss of HBc production and reverse transcription. Furthermore, pharmacological disruption of m5C deposition led to a significant decrease in HBV replication. Thus, our data indicate m5C methylations as a critical mediator of the epsilon elements' function in HBV virion production and reverse transcription, suggesting the therapeutic potential of targeting the m5C methyltransfer process on HBV epsilon as an antiviral strategy.

Hepatitis B virus↗
PubMed1979

Behavior of cervical epithelium during carcinogenesis: autoradiography of tritiated cytidine in the C57BL mouse.

The autoradiographic patterns of the cervical epithelia of 39 virgin C57BL mice after in vivo injection of [3H]cytidine was investigated. Of the 22 animals painted with benzo[a]pyrene for 5 months, 8 developed intraepithelial atypias and 2 had invasive carcinoma. The mean number of silver grains in individual cells increased from histologically normal cervical epithelium through atypical epithelium to invasive carcinoma. It is apparent that the autoradiographic patterns in normal, atypical, and invasive carcinoma cells reflected quantitative differences in cytidine incorporation. These differences may denote increased demand for RNA precursors in the cervical epithelium during carcinogenesis.

Animals↗
PubMed1975

The modified nucleosides of tRNAs. II. Synthesis of 2'-O-methylcytidylyl (3'-5') cytidine.

The synthesis of 2'-O-methylcytidylyl (3'-5')cytidine by the triester method using as protecting groups, 2,2,2-trichloroethyl for phosphate hydroxyl group, p-chlorophenyoxyacetyl for 5-hydroxyl group, methoxymethylidene for 2',3'-cis-diol system, and benzoyl for the exo-amino group of cytidine is presented. The obtained product was characterised by UV, electrophoresis, chromatography and an enzymatic digestion.

Chromatography, Paper↗
PubMed1977

Cytidine 3',5'-monophosphate (cyclic CMP) formation in mammalian tissues.

Mammalian tissues possess the capacity to synthesize cytidine 3',5'-monopHosphate (cyclic CMP) via the enzymatic conversion of cytidine 5'-triphosphate to cyclic CMP by cytidylate cyclase. Cyclic CMP formation occurs best in the presence of manganese or iron, at neutral pH, at 37 degrees C, in the absence of detergents, and with whole tissue homogenate fractions. Thus, mammalian tissues are capable of synthesizing not only cyclic AMP and cyclic GMP, but also cyclic CMP.

Animals↗
PubMed1975

Control of expression of the pyr genes in Salmonella typhimurium: effects of variations in uridine and cytidine nucleotide pools.

The differential rate of synthesis of five of the pyrimidine biosynthetic enzymes coded for by pyrB-F, and the endogenous concentrations of the individual pyrimidine nucleotides were determined in specially constructed mutants of Salmonella typhimurium. In the mutants employed the different pyrimidine nucleotide pools may be manipulated individually during exponential growth. The results obtained indicate the following. (i) The expression of pyrB, pyrE, and pyrF is controlled by a uridine nucleotide in a noncoordinate manner. (ii) The expression of pyrC and pyrD is regulated predominantly by a cytidine nucleotide. Under all conditions investigated, their expression seems to be coordinated, even though the genes are not contiguous on the chromosome. (iii) The low-molecular-weight effectors involved in controlling the expression of the pyr genes are neither uridine 5'-monophosphate nor cytidine 5'-monophosphate, but rather the corresponding di- or triphosphates.

Amidohydrolases↗
PubMed1976

Synthesis of biologically active spin-labelled radioactive cytidine diphosphodiglyceride, a novel probe for biological membranes.

A versatile synthesis of spin-labelled radioactive cytidine diphospho-sn-1,2-diacylglycerol (CDP-diglyceride) has been developed based on the combination of the enzymatic acylation of radioactive sn-glycero-3-phosphate with 12-doxyl stearic acid and the chemical conversion of the thus obtained spin-labelled radioactive phosphatidic acid with cytidine monophosphomorpholi-date into spin-labelled radioactive CDP-diglyceride. The method for the isolation and purification of the latter compound was described. This obtained CDP-[2-3H]diglyceride contained 10% of fatty acids of paramagnetic nature, presumably present as a covalently bound 12-doxyl stearic acid esters. The biological activity was tested by using the synthesized compound as a substrate in the mitochondrial biosynthesis of phosphatidylglycerol. It was found that spin-labelled CDP-[2-3H]diglyceride prepared as described can be converted in the presence of sn-[2-14C]-glycero-3-phosphate into a spin-labelled [2-3H, 2'-14C]phosphatidylglycerol with isolated rat liver mitochondria, establishing therefore that the site of its utilization is identical with the site of phosphatidylglycerol synthesis in isolated mitochondria, i.e. inner mitochondrial membrane. Results described demonstrate that the synthesized spin-labelled CDP-diglyceride can be used as a specific probe for the spin- and radioactive covalent labelling of polyglycerophosphatides of mitochondrial membranes. Some implications and further possibilities in the study of biological membranes using the spin-labelled radioactive CDP-diglyceride are discussed.

Animals↗
PubMed1975

Autotransufsion of 3H-cytidine-labelled blood lymphocytes in patients with Hodgkin's disease and non-Hodgkin patients. I. Limitations of the method.

Autotransfusion of 3H-cytidine-labelled blood lymphocytes followed by autoradiographic evaluation as studied in 11 patients with Hodgkin's disease and pool sizes of lymphocytes. However, it is complicated by two major pitfalls; (1) The free (extracellular) activity of oH-cytidine transfused along with the cell-bound label is sufficient to cause DNA labelling of newly produced lymphocytes in the body. (2) The soluble intracellular pool of 3H-labelled compounds causes an increase of labelling intensity of lymphocyte RNA in the first hours after cell transfusion. Methods to correct for these sources of error are described.

Blood Transfusion, Autologous↗
PubMed1977

Enzymes relevant to cancer chemotherapy II. Heterogeneity of rat kidney uridine kinase following chromatography on Sepharose 6B coupled to N4-(5-amino-Pentyl)-cytidine.

Using Sepharose 6B coupled to N4-(5-aminopentyl)-cytidine at least three different peaks of rat kidney uridine kinase activity have been found. Prior to affinity chromatography the enzyme was partially purified by ammonium sulfate precipitation. The elution was carried out with 0.15 M NaCl or with 0.012 M ATP. The importance of different forms of uridine kinase in eukaryotic cells for cancer chemotherapy with uridine and cytidine analogues is discussed.

Animals↗
PubMed1977

Decreased utilization of [2-14C]orotic acid for the synthesis of cytidine nucleotides in rat liver after administration of alpha-hexachlorocyclohexane.

Administration of alpha-1,2,3,4,5,6-hexachlorocyclohexane (alpha-HCH) to rats decreased the utilization of [2-14C]orotic acid for the synthesis of liver cytidine nucleotides. The specific radioactivities of uridine components of the acid-soluble pool and rRNA increased during the first hours of treatment with the drug. Later on the specific radioactivities of uridine nucleotides remained unchanged, while those of cytidine components decreased gradually. Administration of hydrocortisone increased the incorporation of labelled orotic acid into rRNA cytidylic acid.

Animals↗
PubMed1977

Rate-limiting steps in the cytidine pathway for the synthesis of phosphatidylcholine and phosphatidylethanolamine.

An analysis of the available data on the cytidine pathway for the synthesis of phosphatidylcholine and phosphatidylethanolamine, by the logic derived from the theoretical principles of metabolic regulation, shows that the first two reactions catalysed by choline (ethanolamine) kinase and phosphocholine (phosphoethanolamine) cytidylyltransferase are rate-limiting, whereas the phosphocholine (phosphoethanolamine) transferase step is near equilibrium in rat liver.

Animals↗
PubMed1978

Three-dimensional structures of aspartate carbamoyltransferase from Escherichia coli and of its complex with cytidine triphosphate.

X-ray diffraction studies to nominal resolutions of 3.0 A for unliganded aspartate carbamolytransferase (EC 2.1.3.2)(R32 crystal symmetry) and of 2.8 A for the complex of aspartate carbamoyltransferase with cytidine triphosphate (P321 crystal symmetry) have yielded traces of the polypeptide chains of the catalytic (C) and regulatory (R) chains in the hexameric C6R6 molecules. The independent molecular structures of the liganded and unliganded forms of the enzyme are very nearly identical. In the regulatory chain there is a CTP-binding domain that interacts with an adjacent regulatory subunit and a zinc-binding domain that interacts with the catalytic subunit. In the catalytic chain a polar domain shows interactions between adjacent pairs of C chains to form each trimer C3 while an equatorial domain shows intramolecular C3--C3 interactions. The active site is at or near the interface between adjacent C chains within the trimers. Probably each active center involves amino acid residues from adjacent C chains.

Aspartate Carbamoyltransferase↗
PubMed1978

Depression of cytidine 3':5'-cyclic monophosphate phosphodiesterase activity in developing tissues of guinea pigs.

Changes in levels of the newly discovered cytidine 3':5'-cyclic monophosphate (cyclic CMP) phosphodiesterase in some representative tissues (cerebral cortex, kidney, intestine, liver, heart, and lung) of guinea pigs from various developmental stages (fetus, neonate, pup, and adult) were studied and compared with those of cyclic AMP and cyclic GMP phosphodiesterases in the same tissues. It was observed that the tissue levels of cyclic CMP phosphodiesterase were invariably the lowest in every one of the fetal tissues examined, the highest in the corresponding tissues from the pups and adult, with intermediate levels seen in some neonatal tissues. The patterns of the ontogenetic changes in levels of cyclic AMP and cyclic GMP phosphodiesterase activities, however, were variable and tissue specific. These findings suggest that the depressed cyclic CMP phosphodiesterase activity (hence, the elevated cyclic CMP concentration) is perhaps a common factor in developing tissues undergoing rapid cell proliferation. The data also suggest that metabolism of cyclic CMP is perhaps more closely related to cell proliferation than the metabolism of cyclic AMP or cyclic GMP.

Animals↗
PubMed1978

Migration pattern of splenic lymphocytes after local labelling of the pig spleen with 3H-cytidine.

In normal young pigs splenic lymphocytes were selectively labelled by injecting tritiated cytidine into a splenic artery. 10 h later several lymphoid and non-lymphoid organs were investigated for spleen-derived lymphocytes by autoradiography. The relative and absolute organ distribution of the labelled cells was determined. Labelled lymphocytes appeared rapidly in the peripheral blood reaching a mean labelling index of 4.8%. More splenic lymphocytes were found in thymus dependent areas than in thymus independent areas of lymphoid organs. Nearly 40% of all emigrated lymphocytes homed to lymph nodes and only about 1% in the thymus. A surprisingly high number of splenic lymphocytes were located in the bone marrow and the lung.

Animals↗