Search PubMed⌕ Search

Biomedical subjects

D Shugar

Publications and source records attributed to D Shugar.

At least 163 records · Page 9Linked to original sources
PubMed1975

Pyrimidine nucleoside analogues as inducers of pyrimidine nucleoside catabolizing enzymes in Salmonella typhimurium.

Various structural analogues of cytosine and uracil nucleosides were tested as potential inducers of the nucleoside catabolizing (cyt) enzymes in Salmonella typhimurium. Some analogues, e.g. 5'-O-alkyl cytidines and uridines, resistant to catabolic enzymes, were as effective as the natural inducers cytidine and uridine; but etherification of one of the cis 2' or 3'hydroxyls fully abolished activity, pointing to a requirement of an intact ribose cis-glycol system for activity. A uridine analogue in the syn conformation, 6-methyluridine, a good substrate for uridine phosphorylase, was inactive as an inducer. The behavior of various other analogues, in relation to their structure, conformation and substrate properties, indicated the absence of any correlation between inducing activity and substrate susceptibility. The overall findings are consistent with conclusions derived from genetic experiments. The active analogues apparently act via similar pathways, and probably affect the same regulatory mechanism(s) as the natural inducers.

Cytidine↗
PubMed1975

Photodissociable dimer reduction products of 2-thiopyrimidine derivatives.

Both 4,6-dimethyl-2-thipyrimidine and its 1-methyl derivative undergo polarographic reduction in aqueous medium, via a 1e/1H+ reduction to a free radical which rapidly dimerizes to products isolates and identified as 4,4'-bis-(4,6-dimethyl-3,4-dihydropyrimidin-2-thione) and the corresponding 1-methyl dimer. The dimers may be oxidized electrolytically to regenerate the parent monomers. Both dimers also undergo photodissociation to quantitatively regenerate the parent monomers, in high quantum yield, 0.23 and 0.35 M/Einstein. The correlation between electrochemical and photochemical reductions of 2-thiopyrimidines are discussed, as well as the significance of the dimer photodissociation reactions in relation to nucleic acid photochemistry.

Electrolysis↗
PubMed1975

Fate of heterologous deoxyribonucleic acid in Bacillus subtilis.

CsCl density gradient fractionation of cell lysates was employed to follow the fate of Escherichia coli, phage T6, and non-glucosylated phage T6 deoxyribonucleic acid (DNA) after uptake by competent cells of Bacillus subtilis 168 thy minus trp minus. Shortly after uptake, most of the radioactive Escherichia coli or non-glucosylated T6 DNA was found in the denatured form; the remainder of the label was associated with recipient DNA. Incubation of the cells after DNA uptake led to the disappearance of denatured donor DNA and to an increase in the amount of donor label associated with recipient DNA. These findings are analogous to those previously reported with homologous DNA. By contrast, T6 DNA, which is poorly taken up, appeared in the native form shortly after uptake and was degraded on subsequent incubation. The nature of the heterologous DNA fragments associated with recipient DNA was investigated with Escherichia coli 2-H and 3-H-labeled DNA. Association of radioactivity with recipient DNA decreased to one-fourth in the presence of excess thymidine; residual radioactivity could not be separated from recipient DNA by shearing (sonic oscillation) and/or denaturation, but was reduced by one-half in the presence of a DNA replication inhibitor. Residual radioactivity associated with donor DNA under these conditions was about 5% of that originally taken up. Excess thymidine, but not the DNA replication inhibitor, also decreased association of homologous DNA label with recipient DNA; but, even in the presence of both of these, the decrease amounted to only 60%. It is concluded that most, or all, of the Escherichia coli DNA label taken up is associated with recipient DNA in the form of mononucleotides via DNA replication.

Bacillus subtilis↗
PubMed1975

Heterologous deoxyribonucleic acid uptake and complexing with cellular constituents in competent Bacillus subtilis.

With competent cultures of Bacillus subtilis the uptake of Escherichia coli deoxyribonucleic acid (DNA) is about 50% that for homologous DNA. Uptake of phage T6 DNA, if any, is of the order of 7%, while nonglucosylated phage T6 (T6) DNA is taken up almost as effectively as homologous DNA. Both T6 and T4 DNA interfere only minimally with uptake of homologous DNA; by contrast, T6 DNA competes with homologous DNA as effectively as the latter itself. These results indicate that the glucose residues in the T-even phage DNA, located in the large groove of the DNA helix, reduce affinity for cellular receptors, leading to low binding of T6 DNA. The latter DNA is considerably less degraded by extracellular nucleases than homologous DNA, thus excluding enzymatic hydrolysis as the source of poor uptake. Affinity of DNA for competent cells was also evaluated by the formation, and detection in a CsCl density gradient, of complexes of DNA with cellular constituent(s). Such comlexes, similar to those previously observed with transforming DNA, are formed by E. coli DNA and T6 DNA; in reconstruction experiments the denatured forms of these same DNA samples form complexes when added to the cells before lysis. T6 DNA, on the other hand, does not form such a complex. The possible role of such complexes in transport of DNA to the cell interior is discussed.

Bacillus subtilis↗
PubMed1975

Preparative enzymic synthesis of nucleoside-5'-phosphates.

1. Wheat shoot phosphotransferase has been employed, with p-nitrophenylphosphate as a phosphate donor, to specifically phosphorylate the 5'-position of a variety of nucleosides and nucleoside analogues. The specificity of the enzyme towards the 5'-position of pentose nucleosides is testified to by the complete resistance to phosphorylation of 5'-O-methylcytidine. 2. With the use of ion-exchange chromatography, the foregoing procedure has been applied to the large-scale preparation of nucleoside-5'-phosphates with overall yields of the order of 80-90%. Quantitative recovery of unreacted nucleoside makes it possible to use this method without risk of losses either on a small or large scale with rare nucleosides. It is also applicable to acid- and alkali-labile nucleosides which cannot readily be phosphorylated by chemical procedures. 3. The wheat shoot phosphotransferase also phosphorylated a galactopyranosyl nucleoside, as well as such derivatives as 1-(beta-hydroxyethyl)cytosine and 5-(beta-hydroxyethyl)uracil, showing that the enzyme does not have an absolute requirement for a 5-membered sugar ring, but rather for the presence of a primary hydroxyl group. 4. The phosphorylated derivatives of galactopyranosyluracil, and of both hydroxyethyl pyrimidines, were resistant to 5'-nucleotidase. E. coli alkaline phosphatase converted all three nucleotides quantitatively to the starting compounds. 5. A synthesis of 1-(beta-hydroxyethyl)cytosine is described.

Alkaline Phosphatase↗
PubMed1975

Alkylated cytosine nucleosides: substrate and inhibitor properties in enzymatic deamination.

Cytosine nucleoside deaminase (EC 3.5.4.5) from Salmonella typhimurium LT2 catalyses the deamination of ribo-, deoxyribo- and arabinosyl nucleosides of cytosine alkylated at the C-5, but not at the N3 or exocyclic N4, of the pyrimidine ring. The enzyme was inert towards analogues etherified at the 3'-OH and 5'-OH of the sugar ring; it was active against the 2'-O-methyl derivative of cytidine, but not arabinosycytosine. The N4-and 5'-O-alkyl non-substrate analogues competitively inhibited deamination of deoxycytidine and arabinosylcytosine, the most inhibitory being 5'-O-methylarabinosylcytosine. The alpha anomer of 5'-ethyldeoxycytidine, the 2,2'-anhydro derivative of cytidine, and the 3'-O-alkyl derivatives were neither substrates nor inhibitors. The presence of cytidine deaminase was demonstrated in both granulocytes and lymphocytes from human peripheral blood. The specificity of this enzyme differed significantly from that of the bacterial enzyme, a finding of some relevance in relation to the frequently encountered intracellular deamination of therapeutically active arabinosylcytosine to the inactive arabinosyluracil.

Alkylation↗
PubMed1974

Mung bean nuclease: mode of action and specificity vs synthetic esters of 3'-nucleotides.

Mung bean nuclease hydrolyzes synthetic esters of 3'-nucleotides to nucleosides and phosphate esters; esters of 2'-nucleotides, and 2'--> 5' internucleotide linkages, are resistant. Esters of ribonucleotides are cleaved at 100-fold the rate for deoxyribonucleotides, the increased rate being due to presence of the 2'-hydroxyl and not to differences in conformation. Introduction of a 5'-substituent leads to a 3-fold increase in rate. The rates of hydrolysis vary up to 10-fold with the nature of the base, in the order adenine > hypoxanthine > uracil; and up to 6-fold with the nature of the ester radical. This form of cleavage of esters of 3'-nucleotides is also characteristic for nuclease-3'-nucleotidase activities from potato tubers and wheat, suggesting that one type of enzyme is responsible for all these activities.

Esterification↗