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Biomedical subjects

G Siebert

Publications and source records attributed to G Siebert.

At least 109 records · Page 6Linked to original sources
PubMed1978

A study of microsomal oxidative functions with the aid of a series of N-colchiceyl derivatives.

N-Colchiceyl derivatives are presented as a class of substances which, provided certain structural requirements are met, are oxidatively degraded by microsomal suspensions both at the nitrogen-linked side chain at ring C and at the oxygen-linked side chain(s) at Ring A. The chemical structures of unknown metabolites have been elucidated by comparison with authentic samples whose syntheses are described. Comparative studies indicate structure-dependent preferred sites for the introduction fo oxygen, whose extent correlates rather closely with the partition coefficient in the system n-octanol/ethanol/water. The results demonstrate, with the inclusion of some inhibition data, the suitability of N-colchiceyl derivatives for detailed investigations of microsomal degradative processes.

Animals↗
PubMed1978

Nucleotides and coenzymes in nuclei isolated from rat liver.

In rat-liver nuclei, isolated by the non-aqueous technique, the concentrations and labelling rates of the purine moiety of acid-soluble nucleotides were determined and compared with corresponding data for non-fractionated tissue and nuclei-free cytoplasm. Livers were used from untreated rats, from rats with a highly stimulated synthesis of NAD and from rats following a heavy metabolic load with adenosine. Under all circumstances, the nuclear and cytoplasmic concentrations of nucleotides (e.g. ATP and its dephosphorylated forms, pyridine nucleotides) and of free glucose were practically identical. Specific radioactivities after a pulse with formate also indicated a nucleo-cytoplasmic equilibrium for purine-containing nucleotides. It is concluded that precursor pools for nuclear biosyntheses as well as energy supply for other nuclear activities may be determined by an analysis of the non-fractionated tissue.

Adenine Nucleotides↗
PubMed1978

[Clinical pantographic studies on "immediate side shift"].

The immediate side shift was pantographically recorded, photographed and measured in 32 volunteers with mostly complete dentures. 28 showed initial Bennett movement up to 0.4 mm under tooth contact. Values of between 0.4 and 1.5 mm were demonstrable in only 4 cases. Comparing these investigations in 10 volunteers with and without central supporting peg a clear decrease in measurements could usually be demonstrated.

Adult↗
PubMed1978

[Kinetics of supporting teeth in patients with partial dentures].

In 2 female patients with partial prostheses in the lower jaw, a pilot study was undertaken by means of inductive distance measures into the kinetics of supporting teeth during blank mastication over a period of 10 weeks. 1. Already at the beginning the end supports show unphysiological characteristics of movement during pressing and rubbing. 2. The existing canine guidance shows no abnormal kinetics of the supporting teeth during the excursions. 3. The direction of the kinetics of the supporting teeth changes in embedded part prostheses. 4. The abutment teeth show higher kinetic values after 10 weeks (without embedded partial prosthesis) than in the beginning. 5. In embedded partial prostheses all kinetic values closely approach the physiological norm. The directions on the other hand do not correspond with the physiological norm. The partial prosthesis acts as a splint for the abutment teeth.

Adult↗
PubMed1977

Interaction of colchicine with DNA molecules.

Colchicine (7.5 X 10-6M or 3.3 X 10-5M) was incubated at pH 7.0, 10.0, or 12.0 with high-molecular DNA from salmon sperm (7 X 10-5M or 3.5 X 10-5M DNA-P) at 40 degrees C. Interaction was monitored by UV spectrophotometry; Amax/Amin ratios, difference and additive spectra, and the quantity of colchicine bound to DNA were presented as functions of time, ionic strength and DNA concentration. Using NMR techniques, delta deltav 1/2/deltac values, chemical shifts and half-line widths of colchicine protons were analyzed as a function of the DNA/colchicine ratio, thus proving the interaction between alkaloid and DNA. An intercalation of the tropolone moiety of colchicine between the nitrogenous bases of DNA is suggested.

Animals↗
PubMed1977

[Metabolic behavior of disaccharide alcohols and related substances].

The present study suggests that part of the digestion of disaccharide alcohols is due to microbic processes, primarily in the cecum. The utilization of sorbitol and palatinitol by endogenous metabolic systems seems to be restricted insofar as these substances become accessible to the intestinal flora. Interim products of the bacterial fermentation are likely to be utilized by the host organism.

Disaccharides↗
PubMed1976

Metabolic transformation of colchicine, IV[1]. On the interaction of colchicine and colchiceine with sulfhydryl compounds.

The interaction of colchicine and one of its metabolites, O10-demethylcolchicine (colchiceine), with sulfhydryl compounds was studied in several experimental systems. Colchiceine protects reduced glutathione from oxidation by atmospheric oxygen. Inactivation of enzymes with catalytically essential sulfhydryl groups is prevented by colchiceine. In affinity chromatographic experiments, Agarose-bound colchiceine adsorbs sulfhydryl enzymes which may be eluted specifically by SH-compounds like mercaptoethanol. No such effects are shown by colchicine. The data demonstrate a novel type of biochemical reactivity in the metabolite colchiceine with potential biological relevance.

Adenosine Deaminase↗
PubMed1975

On the bound state of alkali cations in subcellular preparations of rat liver.

Gel filtration and ion-specific electrodes were used together with atomic absorption spectrophotometry in a search for substances in rat liver which are capable of binding alkali cations. In the cytosol, a material which binds K specifically and reduces the ion activity of potassium can be detected. The binding material, which may be destroyed by alpha-chymotrypsin, has been purified about 100-fold. Its molecular weight is around 5 x 10(3). 1 muval K becomes bound per 20-40 amino acid residues; the total binding capacity may amount to 10-15% binding of the K in rat-liver cytoplasm. Washed nuclear residues, consisting mainly of chromatin, are capable of binding Na in a cation-specific mode. DNA and RNA are ruled out as binding material, so it is assumed to consist of protein, and would then contain about 20 amino acid residues per Na. The cation-binding processes are discussed with regard to nucleo-cytoplasmic sequestration of Na and K, with consequences for the cellular chemi-osmotic gradients, and for the regulation of gene activity in the nucleus.

Animals↗