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Biomedical subjects

A Schmidt

Publications and source records attributed to A Schmidt.

At least 703 records · Page 39Linked to original sources
PubMed1979

Differential effects of two interferon-induced translational inhibitors on initiation of protein synthesis.

At least two different mechanisms for the inhibition of mRNA translation operate in extracts of interferon-treated L cells. One is mediated by an interferon-induced protein kinase which, when activated by double-stranded RNA and ATP, phosphorylates the small subunit of initiation factor eIF-2. Addition of the purified interferon-induced protein kinase to L cell extracts, strongly reduces the amount of methionyl-tRNA bound to 40-S ribosomal subunits. The second translational inhibition is due to the synthesis of (2'-5')oligo(adenylate) by interferon-induced enzyme E. The oligonucleotide in turn activates a ribonuclease F constitutively present in L cells. Addition of the purified nuclease with its oligonucleotide activator to L cell extracts produces a strong decrease in polyribosome formation and an accumulation of initiation complex. These experiments differentiate the effects of the two interferon-induced inhibitors on mRNA translation.

Animals↗
PubMed1979

Studies on the substrate specificity of the DNA methylase activity from Escherichia coli K-12.

A partially purified extract of DNA methylases from E. coli K-12 containing DNA-adenine as well as DNA-cytosine methylase activities has been examined with respect to different DNA species as substrates. The results show that the natural content of 6-MAP) in the applied DNA represses the DNA-adenine methylase activity. On the other hand, 5-MC, already present in the substrate does not influence the activity of the DNA-cytosine methylase. DNA from Micrococcus radiodurans, which is completely free of methylated bases served as comparison. Since netropsin preferentially binds to AT-rich regions of DNA, the influence of this oligopeptide antibiotic on the methylation of DNA was investigated. As expected the antibiotic predominantly inhibits adenine methylation of DNA. The degree of inhibition depends on the molar ratio of netropsin to DNA phosphate.

Animals↗
PubMed1979

An interferon-induced phosphodiesterase degrading (2'-5') oligoisoadenylate and the C-C-A terminus of tRNA.

A phosphodiesterase characterized by a generally higher activity on 2'-5' than on 3'-5' phosphodiester bonds was isolated from mouse L cells treated with interferon. A similar enzyme was purified from mouse reticulocytes. The phosphodiesterase 2'-PDi splits the 2'-phosphate bond of pppA2'p5'A2'p5'A, the oligonucleotide activator of ribonuclease F. The level of phosphodiesterase 2'-PDi is increased by interferon treatment of L cells. The phosphodiesterase was also shown to degrade the C-C-A terminus of tRNA and to reduce the amino acid acceptance of tRNA in cell-free extracts, thereby causing a tRNA-reversible inhibition of mRNA translation.

Amino Acyl-tRNA Synthetases↗
PubMed1979

Kinetics of the induction of three translation-regulatory enzymes by interferon.

Three enzymes that cause inhibition of mRNA translation, eukaryotic initiation factor 2 protein kinase PK-i, oligoisoadenylate synthetase E, and phosphodiesterase 2'-PDi, have been recently isolated from interferon-treated cells. We show that the rise in these three enzyme activities may be used to study the response of uninfected cells to interferon. For each enzyme, a specific microassay that can be carried out on extracts from 2-5 x 10(4) monolayer cells from mouse, monkey, or man was developed. With these assays, the kinetics of induction of the three enzymes in mouse L cells are compared. The dose dependence for protein kinase PK-i induction is shown to be similar to that for the development of the antiviral state. Actinomycin D and anti-interferon serum block enzyme induction if added to the cells early after interferon treatment. The quantitative measurements of the intracellular level of these enzymes provide a new and convenient model to study the cell's response to interferon.

Adenine Nucleotides↗
PubMed1979

Distribution of thioredoxins in Cyanobacteria.

The presence of thioredoxin was demonstrated in 20 strains of cyanobacteria as well as in one phototrophic bacterium Rhodopseudomonas sulfidophila and in Thiobacillus denitrificans. Thioredoxin activity was not found in Cyanophora paradoxa and in Porphyridium cruentum using the thioredoxin-dependent PAPS-sulfotransferase activity from Synechococcus 6301 as assay system.

Bacterial Proteins↗
PubMed1979

[Model trials for isolation of soft rot bacteria by media containing pectic substances (author's transl)].

1. Under aerobic conditions bacterial soft rots are caused in the most cases by pectolytic Erwinia, Pseudomonas, and Bacillus spp. 2. Using 7 soft rotting strains several selective media were tested for their ability to sure a quick and exact isolation and differentiation of these pathogens. By bile salt-lactose-medium all Erwinia spp. under test could be isolated. For isolation of pectinolytic Pseudomonas strains the D4 medium of Kado and Heskett was suitable as the best one. 3. By the use of substrats containing pectic substances the results of isolation could be essentially improved: So, a sure differentiation of soft rotting bacteria and saprophytic organisms already upon the substrate and in addition, the isolation of pectinolytic Bacillus strains also became possible. The pectinolytic activity of the test strains on pectin-double layer-media was dependent upon the composition of the basal medium. 4. On the base of the results we obtained an isolation scheme is proposed, that allowed to indicate the pectolytic active bacilli (after heating to 80 degrees C for 10 min) on thioglycollate medium covered by a pectin layer, the Erwinia spp. on Stewart-Medium covered by pectin layer and the pectolytic pseudomonads on FPA-medium described by Sands, Hankin and Zucker (containing citrus pectin) to the equal time. 5. The trials also demonstrated, that the preparing of double layer-media instead of sodium polypectate mostly being recommended in literature lower estered pectic compounds can be used successfully.

Bacillus↗
PubMed1978

Correlation of lysozyme activity with proteoglycan biosynthesis in epiphyseal cartilage.

Pig epiphyseal cartilage (proximal ulna epiphysis) previously incubated into vitro in the presence of sodium [35S]sulfate or [3H]thymidine was either analyzed by autoradiography or separated into 9 morphologically defined consecutive layers and investigated for 35S-incorporation into the guanidinium chloride-extractable proteoglycans and for lysozyme activity. The lowest 35S incorporation and lysozyme activity were determined in the zone of resting cells, but there is a consecutive increase in the rate of proteoglycan synthesis and lysozyme activity toward the diaphyseal cartilage-bone junction, with the maximum at the lower columnar cell zone and a sharp reduction of both parameters at the hypertrophic zone. The maxima of 35S incorporation and [3H]thymidine incorporation do not coincide. The guanidinium chloride-soluble proteoglycans exhibit macromolecular polydispersity. Fractions excluded from as well as retarded by Sepharose 2B gel could be separated and were detected in all zones. The results indicate a correlation of proteoglycan biosynthesis and lysozyme activity in epiphyseal cartilage.

Animals↗
PubMed1978

Analysis of the HLA-ABC linkage disequilibrium: decreasing strength of gametic association with increasing map distance.

1242 HLA-ABC haplotypes of the North German population (Hambrug) as deduced by family analyses are described. They are in perfect agreement with recently published data by Mayr (1977) from Austria (Vienna) in all parameters tested: frequency of the single HLA-alleles, haplotype distribution and linkage disequilibrium values. Gametic association studies revealed that 69.4% of the B and C genes (map distance 0.2cM) 36.9% of the A and C genes (0.6 cM), but only 23.2% of the A and B genes (0.8 cM) were significantly more often combined than expected due to their frequencies. From these findings it seems likely that the linkage disequilibrium within the MHC is rather due to a short evolutionary period than to selective forces. Some observations as to the most common European haplotype A1,B8 are discussed.

Alleles↗
PubMed1978

Diamine oxidase activity in gastric and duodenal mucosa of man and other mammals with special reference to the pyloric junction.

In the gastric mucosa of human subjects and of various mammals methylation was accepted as the main pathway of histamine catabolism. However, augmentation of gastric acid secretion by aminoguanidine, the strong inhibitor of diamine oxidase, indicated an influence of diamine oxidase activity on this secretory process. Therefore a careful reinvestigation of the occurrence of diamine oxidase activity was started from the distal duodenum in the direction of the cardia. In all species studied, diamine oxidase activity decreased from distal duodenum towards the pylorus. In dogs, landrace pigs and in human subjects the diamine oxidase activity clearly exceeded the pyloric borderline gradually becoming zero in corpus or fundus. In rabbits, however, and especially in mini-pigs no diamine oxidase activity was found beyond the pylorus. Among individuals gastric diamine oxidase activity showed a variable prevalence and could not be found regularly in all the subjects. In one patient with prepyloric ulcer a strong influence of pathophysiological processes on gastric diamine oxidase activity could be suspected. Thus, in every alteration of the gastric mucosa under experimental or clinical conditions also an alteration of gastric diamine oxidase activity should be taken into account.

Aged↗