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K Dose

Publications and source records attributed to K Dose.

At least 37 records · Page 2Linked to original sources
PubMed1986

Survival under space vacuum--biochemical aspects.

Exposure to vacuum predominantly causes the removal of water. As a consequence hydrophobic bonds (e.g. of membranes and proteins) are disrupted and metabolism practically comes to a complete halt. Removal of hydrate water also causes substantial changes regarding the structure of DNA (A-structure likely prevails). Some organisms, however, especially bacterial spores and fungal conidia are so well adapted to extreme dryness that substantial fractions of these organisms survive several months of vacuum even at room temperature. In these organisms some vacuum-induced alterations occur that are not readily reversed by readdition of water; mutations become evident and the amount of DNA covalently bound to protein is drastically increased. The mechanisms of these processes and their possible repair are not yet clear. There is evidence that chemical reactions (e.g. dehydration reactions) are involved although they likely proceed at an extremely low rate. Using the dehydration of serin by vacuum as a model system (the resulting amino acrylic acid is converted into pyruvic acid and ammonia after reexposure to water) we could establish that about 3 out of 100 000 serins are finally converted into pyruvic acid after exposure to 10(-6) Torr for 1 week at 55 degrees C In dry Ar the corresponding rate is only about 1.5.

Adaptation, Physiological↗
PubMed1985

Vitamin K epoxide reductase activity in the metabolism of epoxides.

The importance of vitamin K epoxide reductase for the metabolism of a range of structurally diverse epoxides has been investigated. Vitamin K1 epoxide is reduced by rat liver microsomes at a rate of 0.47 nmoles/g liver/min. The rate of menadione oxide reduction is not significantly higher than the non-enzymatic reduction rate. No measurable reduction of benzo[a]pyrene 4,5-oxide, benzo[a]pyrene 7,8-oxide, phenanthrene 9,10-oxide, styrene 7,8-oxide, and dieldrin has been detected, nor could trichothecene T-2 toxin inhibit reduction of vitamin K1 epoxide. Thus, vitamin K epoxide reductase is very specific for vitamin K1 epoxide. Taking into account the range of structurally diverse epoxides investigated and the high specific activities of microsomal epoxide hydrolase and cytosolic glutathione transferase for these epoxides it may be concluded that vitamin K epoxide reductase, in all likelihood, generally does not significantly contribute to the control of epoxides metabolically formed from xenobiotics.

Animals↗
PubMed1984

Photoaffinity cross-linking of the coupling factor 1 from Micrococcus luteus by 3'-arylazido-8-azido-ATP.

The vicinity of nucleotide binding sites and the mechanism of ATP synthesis/hydrolysis have been studied with the bifunctional photosensitive ATP analog 3'-arylazido-8-azido-ATP. 3'-Arylazido-8-azido-ATP is hydrolyzed by the F1-ATPase from Micrococcus luteus in the absence of ultraviolet light. Irradiation, by ultraviolet light, of F1-ATPase in the presence of 3'-arylazido-8-azido-ATP results in the specific formation of cross-links between alpha and beta subunits. The results suggest that a hydrolytic nucleotide binding site is located on a beta subunit at or near an alpha subunit, probably at the interface between these subunits. Such a constellation would permit direct subunit-subunit interactions during ATP synthesis/hydrolysis.

Adenosine Triphosphate↗
PubMed1984

Formation of specific amino acid sequences during carbodiimide-mediated condensation of amino acids in aqueous solution, and computer-simulated sequence generation.

Carbodiimide-mediated peptide synthesis in aqueous solution has been studied with respect to self-ordering of amino acids. The copolymerisation of amino acids in the presence of glutamic acid or pyroglutamic acid leads to short pyroglutamyl peptides. Without pyroglutamic acid the formation of higher polymers is favoured. The interactions of the amino acids and the peptides, however, are very complex. Therefore, the experimental results are rather difficult to explain. Some of the experimental results, however, can be explained with the aid of computer simulation programs. Regarding only the tripeptide fraction the copolymerisation of pyroGlu, Ala and Leu, as well as the simulated copolymerisation lead to pyroGlu-Ala-Leu as the main reaction product. The amino acid composition of the insoluble peptides formed during the copolymerisation of Ser, Gly, Ala, Val, Phe, Leu and Ile corresponds in part to the computer-simulated copolymerisation data.

Amino Acid Sequence↗
PubMed1984

Photobiology in space: an experiment on Spacelab I.

The joint European/US Spacelab Mission I, scheduled for October 1983 for a 9 day lasting Earth-orbiting flight, provides a laboratory system for various disciplines of science, including exobiology. On the pallet, in the experiment ES 029 "Microorganisms and Biomolecules in Space Hard Environment" 316 dry samples of Bacillus subtilis spores will be exposed to space vacuum and/or selected wavelenghs of solar UV radiation. After recovery action spectra of inactivation, mutation induction, reparability and photochemical damage in DNA and protein will be determined. The results will contribute to the understanding of the mechanism of the increased UV sensitivity of bacterial spores in vacuo and to a better assessment of the chance of survival of resistant life forms in space and of interplanetary transfer of life.

Bacillus subtilis↗
PubMed1984

Microorganisms and biomolecules in space environment experiment ES 029 on Spacelab-1.

Bacterial spores are proper test organisms for studying problems of space biology and exobiology. During the Spacelab 1 mission, studies on the limiting factors for survival of Bacillus subtilis spores in free space have been performed. An exposure tray on the pallet of Spacelab 1 accomodated 316 samples of dry spores for treatment with space vacuum and/or the following selected wavelengths of solar UV: > 170 nm, 220 nm, 240nm, 260nm and 280 nm. After recovery, inactivation, mutation induction, reparability, and photochemical damages in DNA and protein have been studied. The results contribute to the understanding of the mechanisms of increased UV sensitivity of bacterial spores in vacuo and to a better assessment of the chance of survival of resistant forms in space and of interplanetary transfer of life.

Atmospheric Pressure↗
PubMed1984

Self-instructed condensation of amino acids into polymers.

In contemporary cells biological information is largely stored in nucleic acids. Therefore, a prerequisite in many theories on the origin of cellular life is the pre-existence of self-replicating polynucleotides that had to be formed by abiotic processes on the prebiotic Earth. It is usually assumed that the spontaneous synthesis of a self-replicating polynucleotide could take place readily. However, serious stereochemical obstacles exist which make Such a synthesis extremely improbable. Amino acids on the other hand, which are abundantly formed in prebiotic simulation experiments, are relatively easily polymerized to macromolecules (protoproteins) that share with modern proteins many properties: e.g., definable non-random structure, selected amino acid sequences, enzyme-like activities and self-assembly into supramolecular structures. Prebiotic polyamino acids are therefore regarded by some scientists, including the present author, as the first informational macromolecules. The origin of this information is the chemical reactivity of the various prebiotic amino acids and their chemical response to their environment. The first informational polynucleotides were likely formed by a polynucleotide polymerase activity of prebiotic protoproteins. A contemporary model for this process is seen, e.g., in the activity of template-free Q beta-replicase.

Amino Acids↗
PubMed1983

Neutron small angle scattering of matched proteoliposomes with incorporated F0F1 ATPase complex from Rhodospirillum rubrum FR1. An approach to the structure of membrane proteins in their natural environment.

Purified F0F1 ATPase from Rhodospirillum rubrum FR1 has been incorporated into lipid vesicles from the partially deuterated phospholipid dimyristoylglycerophosphocholine (DMPC-D54). These proteoliposomes were able to carry out energy transducing reactions. The incorporation of the membrane protein was controlled by freeze fracture electron microscopy. A method for structural research of the membrane protein in its natural environment has been developed by means of neutron small angle scattering. Using the contrast variation technique, the lipid part of the proteoliposomes was matched by adding an appropriate amount of D2O to the solvent. Thus the neutron scattering profile of F0F1 ATPase incorporated into vesicles was separated from the neutron scattering of the liposome. F0F1 ATPase incorporated in a lipid bilayer, as well as the free enzyme, yields a radius of gyration of Rg = 6.0 +/- 0.1 nm which leads to an overall diameter of 15.5 nm. This result suggests that the monomeric form of F0F1 ATPase is incorporated in DMPC-D54 membranes at 20 degrees C.

Adenosine Triphosphatases↗
PubMed1983

Response of soluble and membrane-bound F1 ATPase of Rhodospirillum rubrum to the photoaffinity label 8-azido ATP.

Soluble ATPase (F1 ATPase) and membrane-bound ATPase (chromatophores) of Rhodospirillum rubrum have been photoaffinity labeled with 8-azidoadenosine 5'-triphosphate (8-N3ATP). The specific binding of 8-N3ATP to nucleotide binding sites of the chromatophore-bound enzyme is established by competition experiments and it is suggested that hydrolysis and phosphorylation involve the same nucleotide binding sites. The experimental results also indicate that the function of the coupling factor F1 is influenced by its environment.

Adenosine Triphosphate↗
PubMed1982

Formation of specific amino acid sequences during carbodiimide-mediated condensation of amino acids in aqueous solution.

Carbodiimide-mediated peptide synthesis in aqueous solution at room temperature has been studied with respect to self-ordering of amino acids. Inasmuch as glutamic acid is readily converted into pyroglutamic acid, the peptides formed by copolymerization of glutamic acid with other amino acids are preferentially pyroglutamyl-peptides. Competition experiments were carried out to determine the influence of the amino acid side chains on the reactivity of amino acids and peptides during the dehydration condensation. The results show that the self-ordering process is controlled by both the activated carboxyl component (amino acid or growing peptide) and the incoming amino acid. A condensation of pyroglutamic acid, alanine and another amino acid component Xxx (Xxx = Gly, Val, Leu or Gly-Tyr) preferentially yielded the dipeptide pyroGlu-Ala, but the formation of the tripeptide pyroGlu-Ala-Ala became strongly reduced because of competing reactions. A simple explanation for the observed selectivities is not at hand. Polypeptides were so far only obtained when they were allowed to precipitate in the reaction system. Evidence for the non-random copolymerization of larger peptides is presented as well.

Amino Acid Sequence↗
PubMed1982

Enzyme-linked immunosorbent assay for detection of T-2 toxin.

A microtest plate enzyme immunoassay has been developed for the detection of T-2 toxin. Haptenic T-2 hemisuccinate was immobilized on polystyrene surfaces coated with poly(D-lysine). rabbit antisera against T-2 toxin were added. The binding of the first antibody was detected by addition of an anti-rabbit-immunoglobulin/peroxidase conjugate. After conversion of the substrate 2,2'-azinobis(3-ethyl-2,3-dihydrobenzothiazole-6-sulfonate)/H2O2, the absorbance at 414 nm was monitored. Presence of free T-2 toxin during the first incubation step led to a concentration-dependent lowering of absorbance. The lower detection limit was at about 2 pg per assay. The cross reactivity of T-2 toxin antiserum with other trichothecenes, as determined by ELISA, is weaker than that reported by other authors using a radio-immunoassay technique.

Animals↗
PubMed1981

Ernst Haeckel's concept of an evolutionary origin of life.

In 1865/66 E. Haeckel for the first time suggested an evolutionary sequence in order to explain the origin of the first living cell. Haeckel's concept is compared with modern theories of the origin of life. It is evident that Haeckel has not as yet received the credit that he deserves for his evolutionary concept.

Biological Evolution↗
PubMed1981

Formation of specific amino acid sequences during thermal polymerization of amino acids.

The mechanism of the thermal polymerization (at 180 degrees C) of glutamic acid, tyrosine, and glycine has been studied. Glutamic acid is quickly and almost completely converted into pyroglutamic acid. The only dipeptide that is formed by dimerization of the remaining two amino acids is cyclic glycyl-tyrosine (a diketopiperazine). In a secondary reaction pyroglutamic acid interacts with cyclic glycyl-tyrosine and yields pyroglutamyl-glycyl-tyrosine and pyroglutamyl-tyrosyl-glycine. Other di- or tripeptides are not observed. The preferential appearance of the two pyroglutamyl-peptides has been reported earlier by Nakashima et al. (1977). The present data explain those results. Model experiments show that cyclic glycyl-tyrosine can also be cleaved by other acids or bases. In the presence of acetic acid at 118 degrees C N-acetyl-glycyl-tyrosine is the major product. Partial hydrolysis predominantly yields tyrosyl-glycine. These effects are explained by stereospecific interactions. The results on self-ordering of amino acids during peptide formation are discussed in respect of the origin of prebiotic enzymes and genetic information.

Amino Acid Sequence↗