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Biomedical subjects

R K Zahn

Publications and source records attributed to R K Zahn.

At least 181 records · Page 10Linked to original sources
PubMed1975

Poly(A) polymerase in quail oviduct. Changes during estrogen induction.

A nuclear poly(A) polymerase has been isolated from oviducts of immature quails. It could be purified 4300-fold. The enzyme depends specifically on ATP as substrate and requires Mg2+. The most effective primer for the enzyme is a polynucleotide, isolated from oviduct tissue. A poly(A) sequence to a maximum of 60 AMP residues is covalently linked per primer molecule. The poly(A)-rich product of the enzymatic reaction can be annealed to oligo(dT)-cellulose. The purest fraction does not contain any detectable poly(A)-degrading enzyme activity. Only very low activities of RNA polymerase are present. The poly(A polymerase activity in the assay with ATP is reduced by the ATP analogue, beta, lambda-ATP-methylene-diphosphonate. Both K-m and V are lowered. The ATP analogue is incorporated to a smaller extent into the poly(A) sequence, synthesized by the enzyme. Several other analogues of adenine, adenine nucleosides and adenine nucleotides are without effect on the enzymatic reaction. By these properties poly(A) polymerase can be distinguished from RNA polymerases form I and form II, isolated from the same tissue. Actinomycin D and alpha-amanitin failed to inhibit poly(A) polymerase activity. The activity of poly(A) polymerase has been determined during primary stimulation with the estrogen analogue diethylstilbestrol (daily injection for 5 days), after withdrawal of the hormone for 17 days and after secondary stimulation with the hormone analogue. The enzyme activity does not change during primary stimulation, withdrawal of the hormone or secondary stimulation. However the activity of a poly(A) degrading enzyme, localized in the nucleus, is reduced in oviducts from hormone-treated quails.

Adenine Nucleotides↗
PubMed1975

[Method for determination of the bleomycin inactivating enzyme acitivity in tissues].

An enzyme that inactivates Bleomycin (BLM) can be extracted from tissue. The activity of this enzyme varies markedly in different tissues. In the present paper, a method is described by which the activity of the BLM-inactivating enzyme in different organs and tissues of mice can be determined. The highest activity is found in liver; lower enzyme concentrations occur in the testis, spleen, lung and brain. In skin this enzyme is almost completely missing.

Animals↗
PubMed1975

Deoxyribonucleases activities in human leukemic cells and mouse lymphoblasts.

The deoxyribonuclease activities from human lymphocytes have been compared with the activities from acute lymphocytic leukemic cells and mouse leukemic cells L5178Y using the in situ detection of deoxyribonucleases in DNA-containing polyacrylamide gels following their separation by micro-disc-electrophoresis. A neutral deoxyribonuclease activity is completely missing in leukemic cells of untreated patients while a group of acid deoxyribonuclease activities is increased. A similar deoxyribonuclease pattern can be seen in L5178Y cells. Under medical treatment the increment of the acid deoxyribonuclease activities disappears and the neutral deoxyribonuclease activity reappears.

Animals↗
PubMed1975

Alterations of DNA-dependent DNA polymerase activities in the immature quail oviduct in response to estrogen stimulation.

Administration of diethylstilbestrol, an estrogen analogue, to immature female quails causes an increase of extractable DNA-dependent DNA polymerase activities from the oviduct. At least two forms of polymerases have been determined, a high molecular weight polymerase (210,000 daltons) and a low molecular weight polymerase (34,000 daltons) calculated from column chromatography Sephadex G-200. During the primary hormone stimulation the amount of extractable enzyme reaches a maximum on the fifth day after daily injections of the hormone. In the period of withdrawal the activities decrease and reach values similar to those determined in the unstimulated oviducts. During secondary stimulation the polymerase activities increase again the first day; subsequently the values decrease drastically. The alterations in enzyme activity correlate with the DNA synthesis in the oviduct, as measured by analytical determination of the DNA content.

Animals↗
PubMed1975

Influence of molecular weight of DNA on the determination of anti-DNA antibodies in systemic lupus erythematosus (SLE) sera by radioimmunoassay.

Using a radioimmunoassay (RIA) based on the Farr technique with radioactively labeled 3-H-DNA for quantitative measurements of anti-DNA antibodies in sera of patients with systemic lupus erythematosus (SLE), the influence of molecular weight of DNA (ranging from 0.1 times 10-6 to 22.0 times 10-6 daltons) on binding and precipitation in this system has been investigated. Comparing our results with mathematical models it follows that one antibody molecule is fixed on the average to a statistical DNA segment of 2 times 10-6 to 4 times 10-6 daltons. Furthermore binding capacity of the DNA was found to be independent of the molecular weight, as demonstrated in a double label experiment using 14-C and 3-H-labeled DNA of different size. However, the amount of radioactivity precipitated was found to depend on the molecular weight of the labeled DNA following a non-linear function. It was calculated that a minimal ratio of fixed antibody molecules per a certain size of DNA was necessary for precipitation. The mathematical treatment of the observed non-linear precipitation dependence will be discussed using various statistical models. Our results indicate that the quantitative measurements of anti-DNA antibodies with the Farr technique e.g. for diagnosis and control of SLE in clinical immunology is highly dependent on the molecular weight of the labeled DNA used in the assay system and reliable results are only obtained with DNA of a sufficiently high molecular weight.

Antibodies↗
PubMed1975

Deoxyribonuclease in human parotid saliva.

Deoxyribonuclease (EC 3.1.4.5, EC 3.1.4.6) activities in human parotid saliva were examined by microdisc electrophoresis. Three fractions, differing in their electrophoretic mobility and in their optimal incubation conditions, were characterized. The various enzyme activities were tested at pH 5.0 in 100 mmol with l-minus 1 Na-acetate buffer or at pH 7.04 in 100 mmol with l-minus 1 Tris-HCl-buffer in the presence of different combinations of MgCl(2), CaCl(2), EDTA, and Na(2)SO(4).

Adult↗
PubMed1975

A 3'-deoxymononucleotide-producing nuclease from the marine sponge Verongia aerophoba. I. Purification.

A four-step procedure for purification of a nuclease from the keratinous sponge Verongia aerophoba is described. The extracted material is lyophilized, acidified, and subjected to chromatography on Sephadex, hydroxyapatite, and phosphocellulose. The nuclease is purified about 1,000-fold from the crude extract and approximately 1,600-fold from concomitant acid RNase. Phosphodiesterase is lost after chromatography on Sephadex. The purified enzyme solution contains one single activity as determined by polyacrylamide gel electrophoresis.

Acid Phosphatase↗
PubMed1975

A 3'-deoxymononucleotide-producing nuclease from the marine sponge Verongia aerophoba. II. General properties.

The properties of a 3'-deoxymono-nucleotide-producing nuclease highly purified from the marine sponge Verongia aerophoba are described. The hydrolysis of heat-dentured DNA-proceeds at about five fold the rate of native, double-stranded DNA. The enzyme behaves as an exonuclease by producing 3'-deoxymononucleotides. Kinetic analysis by means of initial hyperchromicity at 260 nm indicates that the enzyme requries 120 mmol/l of mono-valent and 30 mmol/l of divalent cations with a clear dependence on ionic radius. The enzyme has a pH optimum at 4.7, the pH value of the isoelectric point is 6.1. The molecular weight has been evaluated at 62,000.

Animals↗
PubMed1975

Influence of formycin B on polyadenosine diphosphoribose synthesis in vitro and in vivo.

Formycin B inhibited growth of L5178Y mouse leukemia cells in concentrations of less than twice the concentration that inhibits cell proliferation at 50% by cytostasis; at higher concentrations (more than twice the 50% concentration mentioned), the cells were killed. In cells treated with the concentration that inhibits cell proliferation at 50%, the average cell volume did not change. The formycin B inhibitory effect on cell proliferation was reduced by coincubation with nicotinamide adenine diphosphate or adenosine. The biosyntheses of DNA,RNA, and protein in whole cells were sensitively inhibited by formycin B as checked by incorporation studies with radioactive precursors. In addition, the formation of polyadenosine diphosphoribose was reduced even with higher sensitivity; in particular the extent of adenosine diphosphate ribosylation of histone subfraction H1 was reduced. Formycin B has been shown to be an inhibitor for the polyadenosine diphosphoribose polymerase, isolated from oviduct nuclei of quails. Both the chromatin-bound and the soluble enzyme are inhibited competitively; the relative affinity (Ki/Km) of formycin B to the polyadenosine diphosphoribose polymerase is 1.5.

Adenosine↗