PubMed Health⌕ Search

Biomedical subjects

G A Gentry

Publications and source records attributed to G A Gentry.

At least 37 records · Page 2Linked to original sources
PubMed1980

Arabinosylthymine: suppressor of hamster immunoglobulin M formation during primary immune response.

The effect of 1-beta-D-arabinofuranosylthymine (araT) and thymidine (TdR) on the primary and secondary humoral immune responses to Brucella abortus and sheep erythrocytes was investigated. The data indicate that both agents suppress the primary humoral response without significantly altering the secondary response. In addition, the mercaptoethanol-sensitive immunoglobulin component of the total antibody titer was lowered to a much greater extent than was the mercaptoethanol-resistant immunoglobulin component by treatment with ara-T or TdR. Further, the response to B. abortus (a T-independent antigen) seemed to be suppressed more than the response to sheep erythrocytes, a T-dependent antigen. This suggests that subpopulations of lymphocytes may express different sensitivities to araT and TdR.

Animals↗
PubMed1980

Biochemical characterization of equine herpesvirus type 3-induced deoxythymidine kinase purified from lytically infected horse embryo dermal fibroblasts.

Infection of horse KyED cells with equine herpesvirus type 3 (EHV-3) resulted in a sevenfold increase in cytosol deoxythymidine kinase (dTK) activity. The EHV-3 dTK was purified from KyED cytosol dTK by affinity chromatography on deoxythymidine-Sepharose and characterized with respect to its electrophoretic mobility, molecular weight, substrate specificity, phosphate donor specificity, and immunological specificity. The purified EHV-3 dTK migrated in polyacrylamide gels with an Rf of 0.30 and sedimented in glycerol gradients with an S value of 5.13, corresponding to a molecular weight of 83,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis yielded a single band with a molecular weight of 38,000 to 40,000. Antiserum prepared against the EHV-3 dTK induced in KyED cells neutralized the EHV-3-induced enzyme activity but not the dTK purified from uninfected cells. EHV-3 dTK was less sensitive to feedback inhibition to dTTP and had a lower Ki for the antiviral compound 1-beta-D-arabinofuranyosylthymine and a lower Km for the substrate deoxythymidine. These results indicate that infection of cells with EHV-3 results in the induction of a new virus-coded dTK activity which meets the criteria of Jensen for an evolutionary primitive enzyme.

Animals↗
PubMed1979

Purification and biochemical characterization of deoxythymidine kinase of deoxythymidine kinase-deficient mouse 3T3 cells biochemically transformed by equine herpesvirus type 1.

A line of mouse 3T3 cells lacking deoxythymidine kinase (dTK-) was stably transformed to see dTK+ phenotype after exposure to ultraviolet-irradiated equine herpesvirus type 1 (EHV-1). Deoxythymidine kinase (dTK) was purified from the biochemically transformed mouse cells by affinity chromatography on deoxythymidine-Sepharose. The purified dTK from EHV-1-transformed 3T3 cells was identical to the dTK purified from dTK- 3T3 cells lytically infected with EHV-1 with respect to its electrophoretic mobility, molecular weight, substrate specificity, phosphate donor specificity, and immunological specificity. The sedimentation velocity of the purified dTK from the transformed 3T3 cells was similar to that previously reported for the enzyme in lytically infected dTK- 3T3 cells, and its molecular weight was estimated to be 87,000. Antiserum prepared against the EHV-1 dTK induced in horse cells inactivated the dTK purified from the transformed mouse cells. The Km for deoxythymidine (5 micrometers) of purified dTK from the EHV-1-transformed cells was the same as that reported for the EHV-1-induced dTK. These results further support the notion that the dTK acquired by dTK- mouse 3T3 cells after transformation by EHV-1 is of viral and not of cellular origin.

Animals↗
PubMed1979

Arabinosylthymine: inhibitor of splenic lymphocyte macromolecular synthesis in vitro.

The effect of arabinosylthymine on lymphocyte transformation was investigated. Arabinosylthymine was demonstrated not to be cytotoxic for hamster spleen lymphocytes but was found to inhibit the increase in deoxyribonucleic acid and protein synthesis usually observed as a result of mitogen stimulation. These findings suggest that, in addition to being a potent anti-herpesvirus inhibitor, arabinosylthymine is also an immunosuppressive agent.

Animals↗
PubMed1978

Biochemical transformation of deoxythymidine kinase-deficient mouse cells with UV-irradiated equine herpesvirus type 1.

A line of 3T3 mouse cells lacking deoxythymidine kinase (dTK-) was stably transformed to the dTK+ phenotype after exposure to UV-irradiated equine herpesvirus type 1 (EHV-1). Biochemical transformants were isolated in a system selective for the dTK+ phenotype (Eagle minimal essential medium containing 10(-4) M hypoxanthine, 6 X 10(-7) M aminopterin, and 2 X 10(-5) M deoxythymidine). Transformation was accompanied by the acquisition of a dTK activity with immunological, electrophoretic, and biochemical characteristics identical to those of the dTK induced by EHV-1 during productive infection. The transformed cells have been maintained in selective culture medium for more than 50 passages and have retained the capacity to express EHV-1--specific antigens. Spontaneous release of infectious virus has not been detected in the transformed lines, and the the cells were not oncogenic for athymic nude mice. In contrast to normal dTk+ 3T3 cells, EHV-1 transformants were unable to grow in the presence of arabinosylthymine, a drug selectively phosphorylated by herpesvirus-coded dTK's. These results indicate that a portion of the EHV-1 genome is able to persist in the transformed cells for many generations and be expressed as an enzymatically active viral gene product.

Animals↗
PubMed1977

Antiviral activity of arabinosylthymine in herpesviral replication: mechanism of action in vivo and in vitro.

1-beta-d-Arabinofuranosylthymine (ara-T), a metabolite of the sponge Tethya crypta, has shown selective activity against herpes simplex virus (HSV) replication (G. A. Gentry and J. F. Aswell, Virology 65:294-296, 1975). Analysis of HSV-infected and uninfected cell lysates by CsCl isopycnic centrifugation showed that ara-T blocked the incorporation of [(3)H]hypoxanthine into viral deoxyribonucleic acid and, to a large extent, into host deoxyribonucleic acid of infected (but not uninfected) cells. Additional experiments with [gamma-(32)P]adenosine 5'-triphosphate as a radiophosphate donor demonstrated that ara-T is phosphorylated by extracts of HSV-infected BHK cells and not by those of uninfected cells. At an ara-T concentration that almost completely inhibited the growth of LM cells, which had been transformed to a pyrimidine deoxyribonucleoside kinase(+) (dPyK(+)) phenotype by ultraviolet-inactivated HSV-1, the growth of uninfected LM cells was not affected. These results indicate that the viral dPyK is responsible for the selective antiviral activity of ara-T. This conclusion was further supported by experiments that showed that the replication of a variety of dPyK(-) mutants of HSV-1 and HSV-2 were not affected by ara-T and that ara-T inhibited the phosphorylation of deoxycytidine and deoxythymidine by HSV-1 dPyK, but not by host deoxycytidine and deoxythymidine kinases, respectively. Ara-T also selectively inhibited the replication of equine herpesvirus type 1 (EHV-1) in vitro and was effective against EHV-1 infection in vivo in hamsters. Further, EHV-1 was inhibited by ara-T and by bromodeoxyuridine in LM cells lacking a cytosol thymidine kinase, suggesting that EHV-1 induces a dPyK. Finally, spectrophotometric assay for thymine suggested that ara-T is not a substrate for nucleoside phosphorylase of hamster liver, and a microbiological assay indicated that substantial amounts of ara-T were excreted in the urine of uninfected hamsters that had received a single injection of 5 mg of ara-T, the amount given in each injection in the in vivo experiments with EHV-1.

Animals↗
PubMed1975

Metabolism of deoxycytidine, thymine, and deoxythymidine in the hamster.

The ability of growing and of mature Syrian hamsters to anabolize (to liver DNA) or catabolize (to 14CO2) graded amounts of [2-14C]deoxythymidine (TdR), thymine, or deoxycytidine (CdR) was measured in vivo. Of the three precursors, CdR labeled DNA most efficiently and, as expected, incorporation of all three into DNA was greater in younger animals. The catabolism of [2-14C]CdR to respired 14CO2 was dose dependent and showed no signs whatsoever of saturation, even with the highest dose (greater than 20 mumoles/g liver). In contrast, TdR and thymine were catabolized more slowly and saturation was approached with modest doses. The excretion of CdR in the urine was low and independent of dose, while excretion of TdR and thymine was greater and was dose dependent. Rats tested with an intermediate dose of CdR did not catabolize significant quantities to 14CO2, but did excrete considerably more [C]CdR into the urine than did hamsters. These and other findings suggest that, while the rat and the hamster metabolize thymine (and TdR as well) in a similar fashion, they metabolize CdR quite differently, probably because the hamster has a much higher level of nucleoside aminohydrolase which deaminates CdR and related compounds. Because the human also has a very high level of this enzyme, the hamster appears to be a superior animal model for the study of cytosine-containing compounds intended for human use.

Age Factors↗
PubMed1975

Collaborative study of a gas-liquid chromatographic method for the analysis of propazine.

A gas-liquid chromatographic method for the determination of propazine in wettable powder formulations containing about 80% active ingredient was collaboratively studied, using a matched pair scheme. The propazine was extracted from the powder with chloroform, with dieldrin as an internal standard, and chromatographed on Carbowax 20M, using a flame ionization detector. Two samples were analyzed using peak height measurements with the following results (13 collaborators): 1.2% overall coefficient of variation and 1.2% coefficient of variation for the random error. Statistical evaluation of these factors reveals no evidence of systematic error contribution. The method has been adopted as official first action.

Chloroform↗
PubMed1975

Collaborative study of a gas-liquid chromatographic method for the analysis of chlorobenzilate and chloropropylate.

A gas-liquid chromatographic method for the determination of chlorobenzilate and chloropropylate in liquid formulations containing about 46 and 26% active ingredient, respectively, was collaboratively studied, using a matched pair scheme. The samples were dissolved in acetone containing debenzyl succinate as an internal standard and chromatographed on Carbowax 20M, using a flame ionization detector. Analyses of 4 samples by 13 collaborators using peak height measurements showed the following results: chlorobenzilate-2.5% overall coefficient of variation, 1.0% coefficient of variation for the random error, and 0.7% systematic error; chloropropylate-2.0, 1.4, and 0.4%, respectively. The method has been adopted as official first action.

Benzilates↗
PubMed1975

Herpesvirus-induced availability of host DNA to exogenous endonuclease.

Deoxyribonuclease I penetrates herpesvirus-infected L cells and degrades host DNA without interfering with viral multiplication. The DNA of uninfected control monolayers of L cells, disrupted by scraping, is similarly attacked. In contrast, undisturbed L cells are not affected. This suggests that altered cell membrane permeability allows the nuclease to enter the cell, thereby permitting access of exogenous deoxyribonuclease to cellular DNA.

Animals↗