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Biomedical subjects

A M Bobst

Publications and source records attributed to A M Bobst.

At least 55 records · Page 3Linked to original sources
PubMed1980

Reactivity of reverse transcriptase toward (s4U,U)n copolymers and spin-labeled nucleic acid lattices.

Spin-labeled copolymers of 4-thiouridine and uridine (ls4U,U)n] that contain various amounts of spin label (l) were synthesized by either (i) chemical alkylation of the 4-thiouridine-uridine copolymers (s4U,U)n prepared by copolymerizing 4-thiouridine 5'-diphosphate (s4UDP) and UDP or (ii) copolymerization of spin-labeled s4UDP with UDP using polynucleotide phosphorylase. The effect of (s4U,U)n and (ls4U,U)n on avian myeloblastosis virus (AMV) RNA-dependent DNA polymerase (RNA-dependent DNA nucleotidyltransferase, EC 2.7.7.7; reverse transcriptase) was studied to determine whether the presence of potentially reactive thiol groups or spin labels enhances the inhibitory properties of the copolymers as compared to (U)n. Inhibition by (s4U,U)n gradually increases as the percentage of thiolation increases. Enhanced inhibition by (s4U,U)n appears to be due to the interaction of the thiol groups of (s4U,U)n with the thiol group(s) of the polymerase, because inhibition by (s4U,U)n (8% thiolated) in the presence of dithiotreitol resembles that by (U)n. In contrast, inhibition by (ls4U,U)n containing 3% spin label resembles that by (U)n; however, increasing the spin label to 6% or 12% results in enhanced inhibition by (ls4U,U)n as compared to that by (U)n, and dithiothreitol has no effect on enhanced inhibition by (ls4U,U)n. These results suggest that the mechanism of inhibition observed with (ls4U,U)n with a ls4U:U ratio > 1:33 differs from the mechanism for (s4U,U)n and involves complex formation between the spin label and the essential Zn2+ of RNA-dependent DNA polymerase.

Avian Myeloblastosis Virus↗
PubMed1978

Nucleic acid interaction with VERO cells. A temperature barrier in the interaction pattern.

The interaction of VERO cell monolayers with spin (nitroxide)-(labeled polynucleotides (1(N)n) was examined by electron spin resonance (ESR) spectroscopy at various temperatures. Nitroxide labels covalently linked to (A)n, (dUfl)n, (U)n and (A)n . (U)n were used to monitor the interaction. The VERO cells were grown on small quartz plates with a cell viability of 95% or better and then used directly for the ESR studies. The ESR results indicated that the interaction between VERO cells and spin-labeled nucleic acids is temperature dependent. No temperature dependence was found when VERO cells were in contact with nitroxide radicals which were free in solution or covalently bound to Sepharose 4B. The temperature dependence established with nitroxide-labeled nucleic acids indicates that a temperature barrier must exist between 20 and 26 degrees C for the interaction between nucleic acids and VERO cells; namely, at 26 degrees C or above spin-labeled nucleic acids interact significantly with a VERO cell surface; whereas, at 20 degrees C the ESR signal reports no interaction. It is concluded that a temperature-dependent phase transition of membrane components or cell surface products active at 26 degrees C or above play a key role in the nucleic acid cell surface interaction process.

Cell Line↗
PubMed1978

5-O-Alkylated derivatives of 5-hydroxy-2'-deoxyuridine as potential antiviral agents. Anti-herpes activity of 5-propynyloxy-2'-deoxyuridine.

Alkylation of 5-hydroxyuridine or 5-hydroxy-2'-deoxyuridine with various activated alkylating agents in the presence of 1 equiv of NaOH gave a series of new nucleoside analogues which were evaluated for antiviral activity against vaccinia virus, herpes simplex-1 virus, and vesicular stomatitis virus in both primary rabbit kidney cells and human skin fibroblasts. One of these analogues, 5-propynyloxy-2'-deoxyuridine, was a potent inhibitor of herpes simplex virus. Structure-activity considerations suggest that the anti-herpes activity is dependent on the integrity of the acetylene group since substitution of phenyl, p-nitrophenyl, vinyl, carboxamido, or carboxyl for the triple bond led to diminished antiviral activity.

Antiviral Agents↗
PubMed1978

Reverse transcriptase: a monitor for perturbation effects of spin labels covalently bound to nucleic acids.

The sensitive biological assay for reverse transcriptase was used to monitor potential perturbation effects of spin labels covalently bound to various nucleic acids or nucleic acid analogs to the extent of about one label per 100 residues. The inhibitory properties of the spin labeled and unlabeled biopolymers were compared for evaluating possible interference of the reporter group in protein-nucleic acid interaction studies. The amount of inhibitor required for 50% inhibition (ED50) was determined for the competitive inhibitors (U)n, l(U)n, (RUGT,U)n, (Um)n, (A)n, (Am)n, and l(A)n as well as for thenon- or uncompetitive inhibitors (dUfl)n, l(dUfl)n, (dUz)n, and l(dUz)n. The most pronounced inhibition was observed with spin labeled and unlabeled (dUfl)n. The results indicate that the ED50 and the kinetic patterns of inhibition are similar for the spin labeled and unlabeled inhibitors studied. Thus, the presence of a limited number of spin labels in a nucleic acid matrix has little effect, if any, on reverse transcriptase-nucleic acid complexes and most likely on other protein-nucleic acid complexes.

Avian Myeloblastosis Virus↗
PubMed1976

Dependence of interferon induction on nucleic acid conformation.

UV and circular dichroism characteristics of duplex analogs belonging to the (A)n-(U)n and (I)n-(C)n series were determined to assign qualitatively the nature of conformational differences caused by 5-pyrimidine and c7 purine substitutions in such duplexes. Evidence is presented which shows that 5-pyrimidine substitution by bromine or methyl changes the duplex conformation of both series in a similar way, if at all. A c7 substitution in the purine ring affects the duplex conformation of the members in the same series similarly, but the conformational change appears to be different for the two series. To wit, it is proposed that in the duplexes the effect of the change (A)n leads to (c7A)n is an increase of the positive base tilt, whereas the change (I)n leads to (c7I)n causes a decrease where (c7A)n is poly (7-deazaadenylic acid) and (c7I)n is poly(7-deazainosinic acid), respectively. Poly(5-bromocytidylic acid) (br5C)n proved to be useful as a sensor strand for the intepretation of the spectroscopic data. The circular dichroism findings correlate well with observations made earlier on the interferon inducing ability for such duplexes, namely, duplexes based on the (c7A)n are inactive as interferon inducers, whereas duplexes based on (c7I)n are potent inducers. Furthermore, a 5-pyrimidine substitution does not substantially affect the interferon inducing ability, unless the thermal stability of the analog becomes critical, as in the case of (A)n-(br5U)n. Thus, this study provides the first evidence to link the interferon-inducing ability of a nucleic acid to a defined physical parameter of double helix, and reinforces the concept that interferon induction is dependent on the recognition of a particular spatial and steric organization of a double-stranded RNA.

Circular Dichroism↗
PubMed1976

Spectroscopic properties of various 2'(3')-O-aminoacyldinucleoside phosphates analogous to the 3' terminus of AA-tRNA.

Hypochromicity and circular dichroism data are reported for the 2' and 3'-0-aminiacyldinucleoside phosphates cytidylyl-(3'-5')-2'(3')-0-L-phenylalanyl-adenosine, cytidylyl-(3'-5')-2'-deoxy-3'-0-L-phenylalanyladenosine, cytidylyl-(3'-5')-2'-deoxy-3'-0-glycyladenosine, and cytidylyl-(3'-5')-3'-deoxy-2'-0-L-phenylalanyladenosine, all of which can act as analogs of the 3' terminus of AA-tRNA in various partial reactions of protein biosynthesis. Although all these systems have a 2'-OH group in the furanose of the 3'-residue, differences exist in the extent and/or mode of base-base overlap for most of them, except for cytidylyl-(3'-5')-2'(3')-0-L-phenylalanyladenosine and cytidylyl-(3'-5')-3'-deoxy-2'-0-L-phenylalanyladenosine. It is concluded that the biological activity of the above analogs is affected both by the position of the aminoacyl group and the stacking properties of the bases.

Adenine Nucleotides↗
PubMed1976

Correlation of structural transitions in coliphage R17 with its loss of infectivity.

A circular dichroism comparative study of isolated and in situ phage R17 RNA reveals in both cases the same degree of base pairing. However, thermal circular dichroism melting profiles exhibit the presence of free energy of interaction between RNA and capsid protein. It is apparent that the capsid stabilizes the RNA structure with and without the addition of Mg2+. A close RNA capsid association is also derived from pH titration circular dichroism studies. The pH melting of the RNA in situ starts to occur about 0-5 pH unit higher with and without the addition of Mg2+ than the acid denaturation of isolated RNA. A direct correlation between bathochromic CD peak shift to the main position band and loss of survivors is noted for the thermal melting as well as pH titration experiments. It is suggested that the heat and pH induced conformational alterations of R17 RNA in situ coinciding with loss of infectivity occur after an in situ alteration of nucleic acid-capsid protein interaction.

Capsid↗
PubMed1975

Electron spin resonance for detecting polyadenylate tracts in RNA's.

Electron spin resonance is used to detect RNA's that contain polyadenylate tracts. The method depends on the ability of RNA's that contain polyadenylate sequences to associate with poly(2'-deoxy-2'-fluoro)uridylic acid, which has been spin-labeled with 4-(2-iodoacetamido)-2,2,6,6-tetramethylpiperidinooxyl. The formation of the hybridization product can be detected by monitoring the decrease in mobility of the spin probe.

Adenine Nucleotides↗
PubMed1971

Light-induced electron-transfer reactions between chlorophyll a and hydrogenated pteridine derivatives in solution.

Preliminary studies of the formation of cationic 2 - amino - 6, 7 - dimethyl - 4 - hydroxy - 5, 6, 7, 8 - tetrahydropteridine radicals in alcoholic solution are reported. The results indicate that the same type of radical is formed either by oxidizing agents like hydrogen peroxide and iodine, or in a photoinduced reaction with chlorophyll a. A similarity between the epr signal of the light-induced cationic pteridine radical and the photoinduced epr signal II in photosynthesis is observed.

Chlorophyll↗