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Biomedical subjects

R K Zahn

Publications and source records attributed to R K Zahn.

At least 163 records · Page 9Linked to original sources
PubMed1976

Endoribonuclease IV. 2. Further investigation on the specificity.

The poly(A)-specific endoribonuclease IV produces oligo(A) fragments of a chain length of 10 AMP nucleotides. One enzyme molecule performs 1700 cleavages per min; the cleavages occur randomly. The endoribonuclease IV is a nuclear enzyme which is present in the oviduct of quails in a concentration of 40 000 enzyme molecules per cell. Poly(A) segments on mRNA are selectively hydrolyzed by endoribonuclease IV; the poly(A)-free part of the RNA is not affected. After incubation with the enzyme, a residual oligo(A) stretch of 5 AMP nucleotides remains on poly(A)-rich RNA. The endoribonuclease IV does not disintegrate the polyribosomal complex after incubation in vitro and the enzyme has also no influence on the translational capacity of a cell-free protein-synthesizing system.

Animals↗
PubMed1976

Poly ADP-ribosylation of DNA-dependent RNA polymerase I from quail oviduct. Dependence on progesterone stimulation.

Progesterone causes in goblet cells of oviducts of estrogen hormone-stimulated immature quails selectively gene activation without affecting DNA synthesis. This biological model has been used to study the influence of poly ADP-ribosylation during the processes of DNA transcription. Administration of progesterone in vivo causes an increase of the activity of RNA polymerase I and II in isolated nuclei. This increase is accompanied by a marked decrease of the specific activity of poly (ADP-Rib) polymerase. After in vitro ADP-ribosylation of nuclear proteins the template capacity of chromatin for ""exogenous'' RNA synthesis (with E. coli DNA-dependent RNA polymerases) as well as for ""endogenous'' RNA synthesis with DNA dependent RNA polymerases II is not affected, whereas the data presented seem to indicate that the capacity for RNA synthesis mediated by ""endogenous'' DNA-dependent RNA polymerase I might be inhibited after ADP-ribosylation. Evidence is presented to show that a considerable amount of poly (ADP-Rib), synthesized by poly (ADP-Rib) polymerase in isolated nuclei, is linked with RNA polymerase I. The rate of synthesis of poly (ADP-Rib) is dependent on the incubation temperature (optimum at 25 degrees C) and it can be inhibited by the specific inhibitors of poly (ADP-Rib) polymerase nicotineamide, thymidine and formycin B. Poly (ADP-Rib) is probably associated with RNA polymerase I through a covalent linkage. ADP-ribosylated RNA polymerase I has been purified 550 fold with respect to the nuclear extract corresponding to a 4,000 fold purification from the whole cell homogenate. The ratio between poly (ADP-Rib), formed during preincubation of nuclei with NAD, and RNA polymerase I remains almost constant during the purification procedures. The extent of ADP-ribosylation of RNA polymerase I decreases during gene expression. Thus we conclude that poly ADP-ribosylation of this enzyme is one of the regulatory mechanisms by which specificity of DNA transcription is achieved.

Animals↗
PubMed1976

Anti-actomyosin. Influence on adhesive behaviour of eukaryotic cells and of Cuvierian tubules.

The effect of antisera against chicken gizzard smooth-muscle actomyosin and against pectoralis striated-muscle actomyosin on adhesive behaviour of eukaryotic cells (from sea urchin embryos and from a silicious sponge) and of Cuvierian tubules has been studied. The results with sea urchin cells, which require divalent cations for aggregation, showed that antiserum to chicken gizzard smooth-muscle actomyosin inhibited reaggreagation of trypsin-treated cells better than mechanically dissociated cells, while anti-chicken pectoralis striated-muscle had no effect. Primary reaggreagation of trypsin-dissociated sponge cells, in the presence of calcium and magnesium, is also inhibitable by anti-gizzard smooth-muscle but not by anti-pectoralis straited muscle. Anti-gizzard smooth-muscle had no effect on secondary reaggregation of sponge cells mediated by a soluble aggregation factor. Anti-gizzard smooth-muscle inhibited Cuvierian tubule adhesion.

Actomyosin↗
PubMed1976

Species-specific aggregation factor in sponges. V. Influence on programmed syntheses.

Isolated cells from the siliceous sponge Geodia cydonium as well as small primary aggregates (diameter: 70 mum) consisting of them show no increase in rates of programmed syntheses and mitotic activity with time. After addition of a highly purified aggregation factor to a culture with primary aggregates which subsequently form secondary aggregates (diameter: larger than 1000 mum), a dramatic increase of DNA, RNA and protein synthesis occurs. Together with this increase, the cells show a high mitotic activity. The values for the mitotic coefficient reach a first maximum 8 h after the beginning of the secondary aggregation process. The stimulation of the mitotic activity of cells during the aggregation factor induced secondary aggregation process can be suppressed by inhibitors of RNA and protein synthesis as well as by a blocker of DNA synthesis. This finding may indicate that cells from the G0-population enter the proliferating cell pool via the G1-phase.

Animals↗
PubMed1976

Alteration of poly (ADP-Rib) synthesis during progesterone- caused gene expression in oviducts of quails.

The biological model of the selective induction of RNA synthesis in oviducts of estrogen stimulated immature quails by progesterone has been used to clarify whether poly (AD-Rib) is involved in DNA transcription. The chromatin-bound as well as the soluble poly (ADP-Rib) polymerase has been isolated from oviducts and the optimal reaction conditions have been determined. The activities, as measured by the incorporation rates of NAD+ into poly (ADP-Rib), of both, chromatin-bound "endogenous" polymerase (in the absense of "exogenous" DNA and histones) and soluble enzyme (native DNA-lysine-rich histone ratio: 4.3) from progesterone treated quail oviducts, have been determined to be only 30 per cent and 46 per cent respectively, as compared with the activities of the enzymes from the controls. This decrease in incorporation rates is apparently not due to an increased poly (ADP-Rib) degrading enzyme activity. Poly (ADP-Rib) synthesis in vivo was determined by incorporation studies with the precursor (14C) ribose. 12 h after intraperitoneal administration, 0.014 per cent of the total radioactivity was recovered in the oviduct histone fraction, 0.011 per cent in the oviduct nonhistone fraction and 0.009 per cent in the oviduct "HCIextract" containing the histone subfractions f1, f2 and f3. Among these histone subfractions f1 is ADP-ribosylated to the largest extent. ADP-ribosylation of f1 is less extensive in progesterone-stimulated oviducts (65 per cent) than in the controls (100 per cent). The present results suggest that in course of the selective, progesterone-induced DNA transcription the poly (ADP-Rib synthesis might drop.

Animals↗
PubMed1976

The conservation of poly-A-containing RNA during the dormant state of the moss Polytrichum commune.

The moss Polytrichum commune can be dried to less than 2% of free water and kept for some weeks without losing its viability. Upon rehydration of the moss, protein synthesis starts about 60 minutes before incorporation of radioactive precursors into RNA can be observed. Pulse labeled total RNA and poly-A-containing RNA do not show quantitative or qualitative alterations during desiccation up to 20 days.

Drug Stability↗
PubMed1976

Species-specific aggregation factor in sponges. VI. Aggregation receptor from the cell surface.

An aggregation receptor from the siliceous sponge Geodia cydonium has been isolated and purified in an almost pure form. It sediments at about 2-6s, has a buoyant density of 1-51 g/ml in CsCl and elutes from Sephadex G-50 at a Ve/V0 value of 1-311. Chemical analysis revealed that the receptor consists of 81% neutral carbohydrate and 7-5% protein. The activity of the receptor is rapidly destroyed by Na-periodate. The receptor is released from the cell surface after removal of Ca2+ from the medium or after incubation of the cells with trypsin. The depleted cells can be charged again with isolated receptor molecules. The binding of the receptor molecules on the cell surface is prevented in the presence of trypsin. For optimal binding, physiological salt concentrations with respect to NaCl (540 mM NaCl) and Ca2+ ions are necessary. The receptor whose isolation is described in this report, is involved in secondary aggregation processes, which are initiated by a soluble aggregation factor. The primary aggregation of the cells is not influenced by the receptor. Time-course studies with receptor-depleted cells revealed that new aggregation receptor molecules are formed during the aggregation process. By competition experiments it could be shown that high concentrations of soluble aggregation receptor molecules inhibit secondary aggregation. The soluble receptor molecules can complete with surface-bound receptor molecules only if these are not linked with the aggregation factor.

Animals↗
PubMed1976

Determination of the bleomycin-inactivating enzyme in biopsies.

A method for the determination of the Bleomycin-inactivating enzyme is described. The amount of conversion of active Bleomycin to inactive Bleomycin is used as a measure for the determination of the Bleomycin-inactivating enzyme activity. The active Bleomycin is determined in a DNA-dependent DNA polymerase assay; in a certain Bleomycin concentration range the resulting reduction of the activity of the DNA-dependent DNA polymerase is correlated linearly when plotted semilogarithmically. By application of this method it has been found that the activity of the Bleomycin-inactivating enzyme is highest in liver and present in lower concentrations in testis, spleen, lung, brain, and skin.

Bleomycin↗
PubMed1976

Effect of bleomycin on DNA, RNA, protein, chromatin and on cell transformation by oncogenic RNA viruses.

Bleomycin (BLM) exclusively affects thymidine-containing compounds such as DNA and polydeoxyribonucleotides by releasing free thymine and leaving aldehyde functions. Molecular morphology and base sequence of the DNA strongly influence BLM activity. High BLM concentrations, besides modifying DNA into oligothyminic or athyminic nucleic acids, cause strand scissions. Enzymatic DNA and RNA synthesis is strongly influenced by BLM. The inhibition in DNA-dependent DNA polymerase and DNA-dependent RNA polymerase assays is of the non-competitive type. Protein biosynthesis in in vitro systems is not affected by BLM even at high concentrations. BLM turns out to be a strong inhibitor of DNase I and of DNase II; the inhibition is of the competitive type. The enzymatic activities of nucleases using RNA as substrate (RNase A, RNase B, Rnase T1, venom phosphodiesterase I and spleen phosphodiesterase II) are not influenced by this antibiotic. The antibiotic reduces cell proliferation (L5178y mouse lymphoma cells) in vitro in low concentrations by cytostasis and at higher concentrations by cytotoxicity. In BLM-treated L5178y cells, DNA synthesis is strongly reduced, while RNA and protein synthesis are not affected. In vivo, using growing quail oviducts, cell proliferation and cytodifferentiation are markedly inhibited after BLM treatment. This is attributed to the observed inhibition of DNA synthesis. RNA and protein synthesis as well as gene expression are not influenced by BLM under the conditions used. The selective inhibition of DNA synthesis in vivo may be caused by the following mechanisms: (1) competition of BLM with RNA; (2) blocking of the accessibility of DNA in chromatin to BLM, and (3) dependence from the repair processes. BLM inhibits growth of sarcomas, induced by oncogenic RNA viruses in vivo; well-developed tumours show regression after BLM treatment. Transformation of chick embryo fibroblasts by oncogenic RNA viruses in vitro and growth of these viruses is blocked by BLM; the most sensitive period for BLM inhibition is the time during the first period (integration of viral genome into cellular genome?) after infection.

Animals↗
PubMed1975

Separation of deoxyribonucleases (DNases) of normal human stratum corneum and psoriatic scales by micro-disc-electrophoresis.

Normal stratum corneum and psoriatic scales were homogenized and a differential centrifugation was performed. The DNase activity of the individual fractions was investigated by micro-dis-electrophoresis. At pH 5 only in the 600xg pellet and 105.000xg supernatant of normal keratin DNase activity could be observed. However, all psoriatic fractions showed distinct enzyme activities. At pH 7.4 little psoriatic DNase activity could only be demonstrated in the 105.000xg supernatant. Except from the 15.000xg pellet all fractions of normal stratum corneum displayed marked activities. In addition the 105.000xg supernatant showed two different DNase bands.

Deoxyribonucleases↗