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Biomedical subjects

R K Zahn

Publications and source records attributed to R K Zahn.

At least 19 recordsLinked to original sources
PubMed1979

Aggregation of sponge cells. Function of a lectin in its homologous biological system.

For the first time, the biological role of a lectin in the process of reaggregation of single cells from the same species (marine sponge: Geodia cydonium Jam.) is described. The galactose-specific lectin does not promote aggregation, but prevents the antiaggregation receptor from disaggregating cell clumps. Competition experiments showed that the lectin inactivates the antiaggregation receptor by binding to it, most likely via its terminal galactose residues. The lectin converts reversibly aggregation-deficient cells (carrying functional cell membrane-bound antiaggregation receptor molecules) to aggregation-susceptible cells.

Animals↗
PubMed1979

Aggregation of sponge cells. XX. Self-aggregation of the circular proteid particle.

In the extracellular space of the tissue of the sponge Geodia cydonium, circular proteid particles are found which carry as subunits the aggregation factor and a series of glycosyltransferases. Using the technique of velocity sucrose gradient centrifugation, the sedimentation coefficient (S020,w) of the particle-monosomes was determined to be 90. By means of the Svedberg equation a molecular weight of 1.3 . 10(8) daltons could be estimated. The monosomes aggregate in the presence of Ca2+ to higher complexes via disomes, trisomes, and pentasomes. The complexes can be redissociated by dodecyl sulfate but not by EDTA. During the Ca2+-mediated self-aggregation, the particles lose their biological activity with respect to their aggregation promoting function.

Animals↗
PubMed1979

Age-dependent gene induction in quail oviduct. IX. Age-dependent alterations of DNA-bound amino acids.

DNA-amino acids (and DNA-protein) complexes were isolated from oviducts of immature, mature and senescent quails by a procedure which does not involve proteolytic enzymes. The content of DNA-amino acids in the complexes, isolated from animals belonging to three different age classes is almost identical and it amounts to about 10 micrograms/mg DNA. However, the fraction of DNA-amino acids which is resistant to pronase is twice as high in lysates from senescent quails as in those from immature and mature animals. The amount of DNA-bound amino acids is strongly dependent on hormone-induced physiological effects in immature quails. If immature animals were treated with estrogen hormone, which causes in induction both of DNA and RNA synthesis, the level of DNA-bound amino acids increases by 220%. This material has been found to be pronase sensitive which might indicate that the amino acids are present as peptides. Treatment of estrogen-stimulated animals with progesterone or inhibitors of DNA and RNA synthesis antagonizes the estrogen-envoked formation of DNA-associated amino acids. From the data we propose that the amount of proteins and/or amino acids, bound to DNA,is not only age-related but also correlated with the physiological state of DNA in immature and mature animals.

Age Factors↗
PubMed1979

Age-dependent gene induction in quail oviduct. VII. Alteration of DNA polymerase activities in response to progesterone treatment.

The changes of DNA synthesis as well as the alterations of DNA polymerase alpha and beta have been determined in oviducts from immature (35 days old), mature (about 300 days old) and senescent (about 3 years old) quails in response to diethylstilbestrol (DES). The DNA synthesis in oviducts from immature quails is strongly stimulated by DES; after 12 days, values equivalent to those determined in mature and senescent animals are reached. The DNA synthesis in immature oviducts can be reversibly blocked by progesterone administration; no influence is observed in the case of DNA synthesis in mature as well as senescent animals. During DNA synthesis in immature oviducts, stimulated with DES, DNA polymerase alpha is strongly induced. Co-administration of progesterone blocks this enzyme induction in a reversible and strong way. The activity of DNA polymerase alpha is identical in mature and in immature animals (after DES treatment for 15 days); the activity of the same enzyme in senescent animals is about 40% lower than the values found in the younger quails. The activity of DNA polymerase beta is not altered if the animals are treated with DES or with DES and progersterone; however, the basic level of the enzyme in senescent animals in 50% lower than in immature or in mature animals.

Aging↗
PubMed1979

Phosphorylation of arabinofuranosylthymine in non-infected and herpesvirus (TK+ and TK-)-infected cells.

The phosphorylation of arabinofuranosylthymine (araThd) has been studied both in non-infected cells and in those infected with herpes simplex virus (HSV-1, Lennette; HSV-1, IES and HSV-2, D-316). In these experiments, HSV strains were used which either contain (Lennette, TK+ and D-316 TK+) or lack (IES, TK-) the capacity to induce pyrimidine deoxyribonucleoside kinase. It was found that extracellularly administered araThd is phosphorylated to ara TTP via araTMP and araTDP in both non-infected and in HSV-infected cells. The phosphorylating capacity is more than tenfold lower in non-infected cells than in infected cells. Interestingly, cells infected with the TK- strain have a tenfold higher phosphorylating capacity than normal, uninfected cells, a fact which might indicate that host cell deoxythymidine kinase is induced during HSV infection. AraTMP is incorporated into cellular DNA but not into HSV DNA. This finding is in contrast to observations with arabinofuranosyladenine, which is incorporated into both cellular and HSV DNA. In vitro experiments with HSV-induced DNA polymerase show that araTTP strongly inhibits the enzyme activity. Therefore we conclude that the inhibition of HSV DNA polymerase by araTTP (formed intracellularly from araThd) is the explanation for the observed antiviral activity of araThd.

Animals↗
PubMed1979

Aggregation of sponge cells. Isolation and characterization of an inhibitor of aggregation receptor from the cell surface.

From the cell membranes of the sponge Geodia cydonium a component was isolated and purified which inhibits the aggregation factor isolated from the same source; the component was termed anti-aggregation receptor. This molecule was characterized as a glycoprotein (54% neutral carbohydrate) and its molecular weight is in the range of 180,000 One biological site of the anti-aggregation receptor was determined to be D-galactose. Indirect evidence presented seems to indicate that this molecule is present in an active form in aggregation-deficient cells and absent in aggregation-susceptible cells.

Animals↗
PubMed1979

Poly(adenosine diphosphate ribose) synthesis during herpes simplex virus infection.

Immediately after infection of baby hamster kidney cells with herpes simplex virus (HSV), cellular DNA synthesis was blocked, while extensive HSV DNA synthesis began. These dramatic alterations of the control mechanisms for these two DNA synthesizing systems were not accompanied by a change in the poly(adenosine diphosphate ribose) polymerase activity.

Animals↗
PubMed1979

Age-dependent enzymatic poly (A) metabolism in quail oviduct.

The poly(A) metabolism in oviducts from adult and senescent quails has been studied. The incorporation studies by double-labelling of mRNA with [3H]adenosine and [3H]uridine revealed, that after inhibition of transcription by actinomycin D, the incorporation ratio adenosine/uridine increases drastically in adult animals compared with the ratio determined for mRNA from senescent animals. This finding is a hint that in senescent animals the poly(A) stretch of mRNA is shorter than in adult animals. This assumption is supported by the finding that the activity of the extractable poly(A) exoribonuclease is higher in senescent than in adult animals. The activity of poly(A) exoribonuclease is even enhanced after stimulation of senescent animals with progesterone. The activity of the other catabolic enzyme studied, the poly (A) endoribonuclease, as well as the activity of anabolic poly(A) enzyme, the poly(A) polymerase, are almost identical in oviducts from adult and senescent animals. The properties of the catabolic poly(A) enzymes and of the anabolic poly(A) polymerase seem to be identical.

Adenosine↗
PubMed1979

Malignancy-associated DNA-binding protein C3DP from human serum. Further characterization and purification of C3DP retaining its DNA-binding affinity.

C3DP, a malignancy-associated DNA-binding protein from human serum[1], was purified to homogeneity without loss of its DNA-binding affinity. For this purpose normal human serum was submitted to affinity chromatography on Con A-Sepharose and DNA-cellulose and to preparative polyacrylamide gel electrophoresis. The purified C3DP was identified by immunodiffusion and sodium dodecylsulfate polyacrylamide gel electrophoresis and it was shown to bind to DNA by DNA-cellulose chromatography. The isoelectric point of C3DP was determined to 4.9 by isoelectric focusing.

Chromatography, Affinity↗
PubMed1979

[Age-dependent avidin induction. V. Changes on the level of post-transcriptional modification].

For the elucidation of the age-dependent reduction of the avidin induction in the ovidict of quails, studies on the level of the post-transcriptional events were performed. In estrogen-treated young animals, the extractable activity of DNA dependent RNA polymerase II increases by 145% after progesterone treatment, while in old animals no increase is observed. In the presence of actinomycin D the incorporation ratio [3H] Ado/[3H] Urd into mRNA increases by about 80% in the case of mature animals; this value is drastically lower (15%) using old animals. The activities of the poly(A)-degrading enzymes in oviducts of mature animals are lower than those in old ones. After progesterone treatment the activities of these enzymes increase in oviducts from old animals, while in young quails no alteration is observed. The possible consequence of these findings on the chain length of the poly(A) segment of mRNA is discussed with regard to its translation capacity.

Aging↗
PubMed1979

Quantitation of intracellular metabolites of [35S]-6-mercaptopurine in L5178Y cells grown in time-course incubates.

6-Mercaptopurine (6MP) metabolism was quantitatively determined in L5178Y murine lymphoma. Cells grown in time-course incubates with [35S]-6MP were extracted with cold perchloric acid, and the buffered extracts were subjected to high-performance liquid cation-exchange chromatography prior to and after hydrolysis with alkaline phosphatase. Free sulfate, 6-thiouric acid, 6-thioxanthosine, 6-thioguanosine, 6-thioinosine, free 6MP, and 6-methylthioinosine were separated from each other; identified in the radiochromatograms by elution volume, UV spectroscopic data, and enzymatic peak-shifting analyses with purine nucleoside phosphorylase; and quantitatively determined by means of 35S radioactivity. Gross intracellular 35S concentrations remained constant at 5 x 10(-5) M after 1 hr of incubation. 6MP metabolism in L5178Y cells was distinguished into an early phase (to 1 hr of incubation) in which 6MP was predominantly catabolized to 6-thiouric acid and free sulfate, into an intermediate phase (to 8 hr) in which substantial amounts of free 6MP and of ribonucleotides of 6-thioxanthosine and 6-thioguanosine were present while the concentrations of nonnucleotide oxidation products sharply decreased, and into a late phase (to 24 hr) in which the ribonucleotides of 6MP, of 6-thioguanosine and, in particular, of 6-methylthioinosine were the most abundant metabolites.

Animals↗