PubMed Health⌕ Search

Biomedical subjects

E Volkin

Publications and source records attributed to E Volkin.

At least 19 recordsLinked to original sources
PubMed1983

The effect of chemical mutagens on purine and pyrimidine nucleotide biosynthesis.

Nucleotide biosynthesis in Novikoff hepatoma cells is markedly altered by a variety of chemical mutagens, whether the mechanism of mutagenesis is by base substitution, covalent binding (adduct formation), intercalation, or cross-linking of DNA. The compounds investigated (N-methyl-N'-nitro-N-nitrosoguanidine, 4-nitroquinoline 1-oxide, 9-aminoacridine, and mitomycin C), at concentrations that cause some inhibition of RNA and DNA synthesis, bring about a large increase in the pool levels of all four nucleoside triphosphates. At the same time, reactions leading to the synthesis of CTP from exogenous uridine and GTP and ATP from exogenous hypoxanthine are severely inhibited. The formation of UTP from uridine and ATP from adenosine, by more direct phosphorylation reactions, appears relatively unaffected. The increase in nucleotide pool size cannot be accounted for by a corresponding increase in de novo purine and pyrimidine nucleotide synthesis, as experiments with labeled formate and aspartate show similar inhibitions by the mutagens. With the salvage precursors, [3H]uridine and [3H]hypoxanthine, the mutagens can produce a widely divergent reduction in the labeling of RNA-CMP versus RNA-UMP and of RNA-GMP versus RNA-AMP, mostly a result of these agents causing large differences in the specific activities of the respective triphosphate precursors. These observations suggest that, in addition to the reactions with DNA, nucleotide biosynthesis could be another important biochemical target of chemical mutagens.

4-Nitroquinoline-1-oxide↗
PubMed1982

Use of radioisotopes in quantitative studies of lung metabolism.

Quantitatively accurate studies of macromolecule and lipid synthesis in lung and other tissues by using radioactive substrates require detailed knowledge of the specific radioactivity of the appropriate pool of precursor molecules serving the synthetic pathway. A brief summary is provided of how considerations of precursor availability, metabolism, and compartmentation, as well as product remodeling, may affect the accuracy with which rates of protein, DNA, RNA, and lipid synthesis can be measured. Where possible, the application of this material to studies of lung metabolism is discussed, along with approaches that may minimize experimental uncertainties.

Amino Acids↗
PubMed1980

Suppression of the biosynthesis of guanosine triphosphate by protein synthesis inhibitors.

In a prior report (Pike, L.M., Khym, J.X., Jones, M.H., Lee, W.H., and Volkin, E. (1980) J. Biol. Chem. 255, 3340-3347), it was observed that CTP synthesis and concomitant incorporation of CMP into RNA and dCMP into DNA were markedly reduced in cells cultured in the presence of cycloheximide and puromycin. Experiments described here with Novikoff hepatoma cells reveal that the purine biosynthetic pathway is similarly affected. When the cells are subjected to cycloheximide (30 or 60 microgram/ml) or puromycin (100 microgram/ml), there is a substantial reduction in the bioconversion of hypoxanthine, adenosine, and deoxyadenosine into guanylate compared to untreated cultures. Whereas synthesis (counts per min/nmol) of pool ATP was 70 to 100% of controls, that of pool GTP was 20 to 35% of controls. Incorporation of AMP into RNA was 40 to 60% of controls, but that of GMP was only 10 to 25% of controls. Incorporation of dAMP into DNA averaged 10% of controls, but that of dGMP was only 4% of controls. Synthesis of guanylates from formate by the de novo pathway was similarly reduced, but incorporation of guanosine, which enters via kinase action alone, was not disproportionately lowered. These results suggest that protein synthesis inhibitors cause a severely reduced availability of newly synthesized GTP and CTP as well as their deoxy counterparts, dGTP and dCTP, the proximal precursors for the synthesis of RNA and DNA. However, the nanomolar levels of all nucleoside triphosphates remain high, probably as a result of recycling of nucleic acid breakdown products. Thus, reduced synthesis of these compounds may restrict nucleic acid synthesis only if some sort of compartmentation leads to a limitation of these precursors at the site(s) of nucleic acid synthesis.

Adenosine Triphosphate↗
PubMed1980

Chromatin-associated RNA: differential extraction and characterization.

Mammalian cells in different states of cytodifferentiation exhibited different RNA-synthesizing and processing patterns that could be used as markers for phenotypic variability. Inherent in these patterns was an RNA class which was differentially extracted from the cellular homogenate by elevating the temperature and pH of the buffer used in the phenol procedure. This class of RNA was initially designated fraction B (chromatin-associated RNA). In the characterization of fraction B, human myeloma cells labeled for 3 and 24 h were fractionated into subcytoplasmic and subnuclear components and the [3H]-RNA was differentially extracted. After 3 and 24 h labeling 84% and 73%, respectively, of the labeled RNA in the chromatin was extracted in fraction B. Only 10-20% of the polysomal RNA was extracted in fraction B with little enrichment in poly(A) RNA. These and other observations suggested that fraction B was a subpopulation of heterogeneous nuclear RNA which was tightly bound to the chromatin complex.

Chromatin↗
PubMed1979

Nuclear retention of 18S ribosomal RNA by human myeloma cells.

Normal quiescent lymphocytes regulate their ribosome content by selectively degrading newly synthesized 18S ribosomal RNA. Unlike actively dividing HeLa cells, lymphocytes retain 18S ribosomal RNA in the nucleus after synthesis instead of immediately transporting it to the cytoplasm. Subcellular fractionation of the highly differentiated human neoplastic lymphocyte RPMI-8226 reveals that this cell line also retains 18S ribosomal RNA in the nucleus, a trait not displayed by the less differentiated human lymphoblastoid cell line RPMI-4265. These observations suggest that neoplastic cells can be phenotypically characterized by their ribosomal RNA processing patterns.

Animals↗
PubMed1977

RNA synthesis and processing as a measure of phenotypic variability in cytodifferentiation and neoplasia.

Neoplastic cell lines exhibit RNA synthesis and process patterns which are related to phenotypic attributes more complex than merely the rate of proliferation. Mouse neuroblastoma cells of the same genotype but different differentiated states have different ribosomal RNA precursor processing patterns, while plasmacytoma cells of different genotypes but the same differentiated state have the same pre-ribosomal RNA processing pattern. In addition, our observations indicate that chromatin-associated RNA is involved in cytodifferentiation and is closely related to phenotypic variability. When neuroblastoma cells are induced to differentiate, there is a 2- to 3-fold increase in the labeling of chromatin-associated RNA. Both of the differentiated cell lines, human myeloma and mouse neuroblastoma, have slow-labeling, stable chromatin-associated RNA while this same fraction from HeLa cells is labeled rapidly and is unstable.

Cell Differentiation↗
PubMed1976

Wasting of 18 S ribosomal RNA by human myeloma cells cultured in adenosine.

When human myeloma cells are pulsed for one hour with 3H-uridine and chased for six hours in fresh medium containing unlabeled uridine, the processing of 45 S rRNA precursor into the stable 28 S and 18 S rRNA components can be followed. However, when the cells are chased in exogenous adenosine instead of uridine, the accumulation of 18 S rRNA is selectively inhibited. Cells pulsed with 3H-adenosine and chased in the absence of exogenous nucleosides exhibit normal rRNA precursor processing, while cells pulsed simultaneously with 3H-uridine and 3H-adenosine and chased with uridine and adenosine are deficient in labeled 18 S rRNA. Consequently, the inhibition of 18 S rRNA accumulation by adenosine is not an artifact of labeling nor is it relieved by an equal molar concentration of uridine. The wasting of 18 S rRNA in human myeloma cells is similar to that reported to occur in normal lymphocytes during the quiescent state.

Adenosine↗