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Biomedical subjects

D Falke

Publications and source records attributed to D Falke.

At least 109 records · Page 6Linked to original sources
PubMed1977

Thymidine transport in herpesvirus hominis type 1 and 2 infected BHK 21 cells.

Increase of dThd-uptake 4 to 12 h after infection of BHK or primary rabbit kidney cells with Herpesvirus hominis of type 1 or 2 can be considered as an early function of the virus genome, because the presence of Cyd-Ara does not prevent the increase of uptake. However, increase of uptake can be prevented by addition of actinomycin D and cycloheximide early in the synthetic cycle. Two modes of uptake have been differentiated by kinetic analysis: at low substrate concentration dThd is taken up by 'facilitated transport', whereas at high substrate concentration (above 2-5 micronM) simple diffusion takes place. The Km of transport of normal BHK or primary rabbit kidney cells (1-4 or 0-5 micronM respectively) is not changed after infection. Only the Vmax increases from 8 to 26-6 pmol in BHK cells or from 2-9 to 9-0 pmol in primary rabbit kidney cells. This indicates that 'carrier sites' with identical affinity for dThd-transport are responsible for the increase of transport after infection. This increase of transport is correlated with the induction of a virus coded thymidine kinase (TK) and not with different types of c.p.e. or cellular damage. Transport of BdUrd increases in a similar manner to that of dThd after infection; transport of dCyd or dUrd increases only slightly, whereas the mechanism of dAdo or Urd uptake by infected cells is quite different.

Animals↗
PubMed1976

Biochemical classification of herpes simplex virus types 1 and 2, and of intermediate strains on the basis of different susceptibilities of thymidine kinase to thymidine analogues.

Herpes simplex virus (HSV) type 1 can be differentiated from HSV type 2 on the basis of the sensitivity to 2'-deoxythymidine-5'-monophosphate of thymidine kinase induced in primary rabbit kidney cells. Whereas thymidine kinase induced by five strains of HSV type 1 (TK 1) is stimulated by suitable concentrations of 2'-deoxythymidine-5'-monophosphate, thymidine kinase induced by eight strains of HSV type 2 (TK 2) is inhibited. On the other hand, TK 2 is strongly inhibited by 2'-deoxythymidine-5'-triphosphate and by 2-bromo-2'-deoxyuridine-5'-triphosphate. The investigation of TK induced by six freshly isolated strains of HSV cross-reacting in neutralisation tests revealed two strains which induced TK 1 and two strains which induced TK 2. Two other strains induced thymidine kinase, the activity of which under the influence of these thymidine analogues was between that of TK 1 and TK 2. The properties of thymidine kinase remained constant after cloning the virus and thus is a genetically fixed trait due to recombination which could well occur in vivo.

Bromodeoxyuridine↗
PubMed1975

Uptake of [3H] thymidine and cell DNA synthesis during the early multiplication phase of herpesvirus hominis in BHK cells.

Experiments about the interaction of herpes viruses with BHK-cells during the first 6 h after infection concerning uptake and incorporation of dThd have been reported. During adsorption and penetration, the inhibition of uptake and of incorporation of [3H] dThd is sensitive to heat, but not to ultraviolet irradiation or cycloheximide. The eclipse is characterized by a strongly increased uptake of [3H] dThd and by inhibition of cell DNA synthesis. Both are sensitive to ultraviolet irradiation of the particles and cycloheximid treatment of the cells. It is concluded that the events during adsorption and penetration are dependent on the particles themselves, whereas the events during the eclipse depend on the activity of the viral genome. The implications of the findings are discussed.

Cell Line↗
PubMed1975

Influence of double infections on the induction of thymidine kinase by UV-irradiated herpes simplex virus types 1 and 2 and pseudorabies virus.

Simultaneous infection of primary rabbit kidney cells with HSV type 1 TK+ and a TK- strain results in a mutual influence of both viruses on the induction of thymidine kinase (TK). TK+ virus has an enhancing and TK- virus a depressing effect on TK induction by a superinfecting TK+ virus. The enzyme induction depends on the ratio of multiplicities of both viruses. The mutual influence on TK induction depends further on the time of addition of the superinfecting virus: the effect of the second virus can still be observed when given 6 hours after primary infection. Identical phenomena can be observed using combinations with HSV type 2 or Pseudorabies viruses. The ability of HSV to induce TK is progressively inactivated with increasing the time of UV-irradiation. The depressing effect of a TK- strain and the stimulating effect of a TK+ strain on superinfecting TK+ strains is UV-sensitive: after 6 minutes of UV-irradiation neither inhibition nor stimulation of TK induction by a superinfecting TK+ strain can be observed. Infection by long-term (20 minutes) UV-irradiated TK+ strains results in a depression of TK induction by a superinfecting TK+ virus. Long-term irradiation of the TK- virus does not show this effect. Cytosine-arabinoside has no effect on the mutual influence of TK induction by TK+ and TK-strains; the phenomenon of mutual depression therefore has to be considered an early process.

Cell-Free System↗
PubMed1975

Regulation by thymidine monophosphate and other nucleotides of thymidine kinase activity in extracts from primary rabbit kidney cells infected by HSV types 1 and 2.

In an attempt to differentiate between thymidine kinase (EC.2.4.1.21) induced by herpesvirus hominis type I (TK I) and type 2 (TK2), the different susceptibilities to the modifying effects of some thymidine analogues proved to be useful criteria: (I)2'-deoxythymidine-5'-triphosphate (dThd-5'-PPP) inhibits TK 2 at a concentration of 0-125 mM by 90%, whereas TK I is inhibited at 4-03 mM by 50%. (2) 2'-deoxythymidine-5'-monophosphate (dThd-5'-P) competitively inhibits TK 2 at all concentrations tested. On the other hand, the direction of its effect on TK I is concentration dependent: at 500 mum it stimulates and at 8 mM inhibits TK I activity. During enzyme kinetic studies, TK I displays substrate inhibition which is reversed by dThd-5'-P. This result explains the stimulating effect of dThd-5'-P at 500 muM. This phenomenon suggests the existence on the enzyme molecule of a second binding site for dThd which mediates substrate inhibition and which can be occupied also by dThd-5'-P. After polyacrylamide gel electrophoresis of TK I, the stimulation by dThd-5'-P disappears, suggesting the separation of the second binding site from the catalytic centre.

Cell-Free System↗
PubMed1975

Enhancement of phagocytosis by Compound 48/80 and its influence upon Ca++-dependent ATP-ase.

A new activity of p-methoxy-phenylethyl-methyl-amine condensed by formaldehyde (Cpd 48/80) has been established: enhancement of phagocytosis. This property seems to be correlated to its ability to activate lysosomes. Enhancement of phagocytosis is discussed in relation to the virus penetration process. Furthermore it was found that Cpd 48/80 and to a smaller degree the dimer inhibit the Ca++-dependent ATP-ase (E. C. 3.6.1.3.) from human red blood cells. The enzyme from bovine myosin is not inhibited by the dimer, but somewhat more by poly-THIQ (7-methoxy-tetrahydroisoquinoline condensed by formaldehyde) than by Cpd 48/80. These properties are discussed in relation to a general hypothesis of virus-induced giant cell formation. Finally it has been shown that the drug does not influence the PHA-stimulation (phytohemagglutinin) of lymphocytes, indicating selectivity of its activity.

Adenosine Triphosphatases↗