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Biomedical subjects

R K Zahn

Publications and source records attributed to R K Zahn.

At least 145 records · Page 8Linked to original sources
PubMed1978

In situ assay of poxvirus-induced and virion-contained deoxyribonucleases in DNA polyacrylamide gels.

Cowpox virus and vaccinia virus WR specific DNases were identified by an in situ assay using DNA-containing acrylamide gels. A DNase present in the isolated virions of strain cowpox and vaccinia WR was identified. Its properties as determined by the in situ assay resembled those of the well-characterized DNase V1. The assay was also used to follow the time course of 'acid' DNase induction by cowpox virus in primary chick embryo fibroblasts.

Cells, Cultured↗
PubMed1978

The major fraction of deoxyribonuclease activity from human urinary proteins. Purification and properties.

The major fraction of deoxyribonuclease activity from human urinary protein was purified 40-fold in about 14% yield. The enzyme shows an isoelectric point at pH 4.2 and has a molecular weight of 33,600+/-3,000. Optimum activity was shown at pH 6.8 in the presence of 12.5 mmol/l Mg2+ plus 1 mmol/l Ca2+. The enzymic reaction is inhibited by high ionic strength (greater than 300 mmol/l Na+). The purified enzyme readily hydrolyzes native DNA to oligodeoxyribonucleotides with an average chain length of 5.3+/-0.2 after exhaustive digestion. Therefore, this endonuclease may be designated as neutral deoxyribonuclease (deoxyribonucleate oligonucleotidohydrolase, EC 3.1.4.5).

Deoxyribonucleases↗
PubMed1978

Species-specific aggregation factor in sponges. VII. Its effect on cyclic amp and cyclic gmp metabolism in cells of Geodia cydonium.

In dissociated single cells from the sponge Geodia cydonium, DNA synthesis is initiated after incubation with a homologous, soluble aggregation factor. During the DNA-initiation phase the cyclic AMP- and cyclic GMP levels vary drastically; the cyclic AMP content drops from 2.2 pmol/10(6) cells to 0.3 pmol/10(6) cells while the cyclic GMP content increases from 0.6 pmol to 3.7 pmol/10(6) cells. The activity of neither the adenylate cyclase nor of the guanylate cyclase isolated from cells which have been incubated for different periods of time with the aggregation factor, is changed. The soluble as well as the particulate enzyme activities were checked in vitro. The cyclic nucleotide receptors have been isolated from the sponge cells and characterized with respect to their molecular weight, dissociation constant for cyclic AMP or cyclic GMP and intracellular concentration. None of these parameters are altered during aggregation factor-mediated DNA initiation. From these data it is concluded that the regulation of cyclic nucleotide levels is a consequence of a changed activity of nucleotide cyclases or of phosphodiesterases, but this is presumably not caused by a changed rate of synthesis of nucleotide cyclases or of cyclic nucleotide receptors.

Adenylyl Cyclases↗
PubMed1978

Tubercidin metabolism in mouse L5178y cells in vivo and in vitro.

Tubercidin (7-deazaadenosine) is a strong inhibitor of cell proliferation in mouse L5178y cells. Radioactive tubercidin is incorporated into DNA and RNA. Poly(A)-containing RNA shows the highest specific radioactivity. The amount of low molecular weight 4S and 5S RNA is diminished to some extent under the influence of the compound. Tubercidin triphosphate is a potent inhibitor of DNA-dependent DNA polymerases alpha and beta, and the DNA-dependent RNA polymerases I, II, and III, although the efficiency of its incorporation is lower than of dATP and ATP. Tubercidin triphosphate also seems to be a good substrate for the Mg2+-dependent poly(A) polymerase.

Animals↗
PubMed1977

Single-step separation of major and rare ribonucleosides and deoxyribonucleosides by high-performance liquid cation-exchange chromatography for the determination of the purity of nucleic acid preparations.

A method is described for the separation of 13 major and minor ribo- and deoxyribonucleosides in a single chromatographic run using high-performance liquid chromatography on strongly acidic cation-exchange columns. The method proved useful for the routine determination of small amounts of ribonucleic acid impurities in deoxyribonucleic acid preparations and vice versa. About 3% or even less of nucleic acid contamination in a given sample can be easily detected and quantitatively determined under the conditions used.

Chromatography, High Pressure Liquid↗
PubMed1977

The quantitative determination of metabolites of 6-mercaptopurine in biological materials. II. Advantages of a variable-wavelength HPLC spectrophotometric detector for the determination of 6-thiopurines.

The advantages of a variable-wavelength spectrophotometric detector for use in high-performance liquid chromatography are demonstrated with the detection of 6-mercaptopurine metabolites in cell extracts. 6-Methylthiopurines, unsubstituted 6-thiopurines and 6-thioguanines are most sensitively detected at 291, 322, and 342 NM, respectively. Compared with detection at 254 nm, the sensitivity at these wavelengths is about one to two orders of magnitude greater. Furthermore, in the 291-355-nm range, common purines, which are normally contained in cell extracts as free bases, nucleosides and nucleotides exhibit only minute absorbances and so do not interfere in quantitative determinations of 6-thiopurine compounds.

Animals↗
PubMed1977

Alterations of activities of ribonucleases and polyadenylate polymerase in synchronized mouse L cells.

The activities of the three known catabolic and the one anabolic polyadenylate enzymes have been determined in synchronized L5178y cells: endoribonuclease, exoribonuclease, 5'-nucleotidase and poly(A) polymerase (Mg2+-dependent). These four enzymes were found primarily in the nuclear fraction. The activity of poly(A) polymerase remains essentially constant during the transition from G1 to S phase. However, the poly(A) catabolic enzyme activities increase parallel with DNA synthesis; the endoribonuclease activity increases 4-fold during G1 to S phase, the exoribonuclease and the nucleotidase activities increasing 30-fold and 16-fold. During the S phase the poly(A)-degrading enzymes are far more active than the poly(A)-synthesizing activity of poly(A) polymerase. We conclude that in L5178y cells the poly(A)-degrading enzymes probably function in regulation of the post-transcriptional net-polyadenylation of heterogeneous nuclear RNA during the phase of DNA synthesis.

Cell Division↗
PubMed1977

Species-specific aggregation factor in sponges. Sialyltransferase associated with aggregation factor.

The sialyltransferase (= glycoprotein-sialic acid transferase) was studied in the sponge Geodia cydonium, a mesozoan organism. The experiments were performed both in intact cellular and in isolated enzyme systems. It is shown, that desialylated cells show a lower aggregation potency than the controls. During aggregation enzymic sialylation of desialylated sponge cells occurs in the presence of an aggregation factor, which is associated with a high molecular weight particle. The sialylation process is temperature-dependent and can be inhibited by N-ethylmaleimide. Sialylation occurs predominantly at a distinct cell surface component, the aggregation receptor. The sialyltransferase was isolated and purified by the following steps: Sepharose 4B, CM-cellulose, Nonidet treatment, and Sephadex G-100. By this procedure the enzyme was purified 680-fold with a 31% yield. The sialyltransferase is originally associated with the high molecular weight particle also carrying the aggregation factor. In the last step the aggregation factor was separated from the sialyltransferase. The enzyme catalyzes the transfer of sialic acid from CMP-sialic acid to the desialylated aggregation receptor. The molecular weight of the sialyltransferase has been determined to be 52,000. Kinetic studies revealed no lag phase and a dependence on enzyme concentration. The purified transferase has a pH optimum of 7.75 and requires 200 mM NaCl for activity. No requirement for Mg2+ or Ca2+ could be observed. The reaction is inhibited by 10 micronM N-ethylmaleimide.

Animals↗
PubMed1977

Inhibition of herpesvirus DNA synthesis by 9-beta-D-arabinofuranosyladenine in cellular and cell-free systems.

9-beta-D-Arabinofuranosyladenine 5'-triphosphate (ara-ATP) is an inhibitor both of DNA polymerase-alpha and -beta from noninfected rabbit kidney cells and of the DNA-dependent DNA polymerase induced by herpes simplex virus Type 1 (strain IES). The studies were performed with partially purified enzymes, and each of the different polymerase preparations contained only one DNA-dependent DNA polymerase species. These enzymes were inhibited in a competitive manner. The HSV-induced DNA-dependent DNA polymerase was 39-fold more sensitive to ara-ATP than was cellular DNA polymerase-beta and 116-fold more sensitive than cellular DNA polymerase-alpha. The affinity of the HSV-induced enzyme for ara-ATP was only slightly influenced by the use of different template/initiators in the enzyme assays. In intact cell systems DNA synthesis was affected by 9-beta-D-arabinofuranosyladenine (ara-A) as indicated by the reduced incorporation of deoxythymidine. In herpesvirus-(strain Lennette)-infected cells, however, ara-A shows no influence on the incorporation on deoxythymidine into cellular DNA, but it substantially reduces the incorporation into viral DNA. Ara-A itself is incorporated into both cellular and herpesviral (strain Lennette, D-316 and IES) DNA during DNA synthesis.

Cell-Free System↗
PubMed1977

Bleomycin-sensitivity test: application for human squamous cell carcinoma.

Bleomycin (BLM)-inactivating enzyme activity, which is probably a parameter for the efficacy of this antibiotic in cancer therapy, was determined in biopsies from human carcinomas in the head and neck region. Twenty-three cases were studied. It was found that highly differentiated as well as moderately differentiated squamous cell carcinomas had low extractable activities of this enzyme, comparably to those found in normal skin tissue. Slightly differentiated as well as undifferentiated carcinomas (only one case) had increased enzyme activity. Parallel experiments estimating the total extractable thiol content in the biopsies gave no obvious correlation. The results are discussed in the light of the reported BLM efficacy in the treatment of differently differentiated squamous cell carcinomas.

Bleomycin↗
PubMed1977

Filter paper disk techniques for assay of nucleotidase.

A DE filter disk technique for assaying the activity of nucleotidase is described. This method is based on the observation that nucleotides bind to the filters at 5 mM Tris-HCl (pH 7.8) while nucleosides do not. As parameter for the nucleotidase activity the decrease of bound nucleotides is determined. In parallel experiments the amount of the product (nucleoside) formed can be measured by DEAE Sephadex column chromatography. The filter disk technique can be applied for the determination of vmax and Km of a nucleotidase by using different ribonucleosidase monophosphate substrates.

Adenosine Monophosphate↗
PubMed1977

Consequences of detergent pollution of the sea: effects on regenerating sponge cubes of Geodia cydonium.

Regenerating cubes of the sponge Geodia cydonium cyconium were used as a model in the investigation of detergent pollution in the sea. The anionic detergent sodium dodecylsulphate (SDS) and a 1:1 mixture of Faks and Radion, two commercial laundry detergents, were used in the concentration range from 1 X 10(-9) g/ml (1 ppb) to 1 X 10(-5) g/ml. It is shown that SDS is taken up, weakly accumulated but not incorporated into the macromolecular fractions of the sponge. At concentrations of 0.1 ppm and above, SDS decreases the uptake of thymidine, uridine and phenylalanine into the acid-soluble sponge fraction. Their incorporation into the acid insoluble fractions, which have been isolated, was different from the controls at 10 ppb and higher levels. Faks and Radion were less active by a factor of 10. However, they showed similar effects. The chemical composition of the regenerating sponge cubes with respect to DNA, RNA and protein content has been evaluated. The alterations are less pronounced on detergent incubation than precursor uptake. The use of the cetyltrimethyl-ammoniumbromide-turbidity-dilution technique reveals drastic qualitative changes in the nucleic acid fractions. The relevant literature on biological effects of detergent is listed. It is shown that this investigation extends the scale of known effects far into the low and pollution-relevant concentration levels.

Animals↗