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At least 37 records · Page 2Linked to original sources
PubMed1978

Comparison of Artemia salina and Escherichia coli ribosome structure by electron microscopy.

The structure of eukaryotic Artemia salina and prokaryotic Escherichia coli ribosomes has been compared by electron microscopy. Despite the established differences in size and in the amount and proportion of the protein and RNA moieties, both types of ribosomes appear to have substantial similarity in the overall shape and in the mutual orientation of the subunits on the monosome. The small subunit is located in the "crown" region of the large subunit lengthwise between the two side crests. However, high-resolution electron microscopy reveals distinct differences in the fine structure of both small and large subunits. The 40S A. salina subunit with three structural domains is more complex than the corresponding E. coli subunit. The 60S A. salina subunit has a less expressed "crown" region and shows a knob-like protrusion in the base. Structural asymmetry is a characteristic feature common to subunits and monosomes from both A. salina and E. coli.

Decapoda↗
PubMed1978

Electron impact mass spectra of 1-methyl-oestra-1,3,5(10)-trienes having intact and 13,17-seco-D-ring structures.

Electron impact mass spectra of 1-methyl-oestra-1,3,5(10)-trien-17-one, its oxime, the homologous 18-norketone, 1-methyl-oestra-1,3,5(10),13(18)-tetraene-17-carbonitrile and the corresponding 13,17-seco epoxide are described. The major fragmentation pathways of these compounds are reported and discussed in relation to their structures, and the structures of the ions m/e 144, 157, 170 and 183 characteristic of the 1-methyl-oestratriene skeleton are described. The relative abundances of these characteristic ions were shown to relat to the presence or absence of a 13,17-seco-D-ring in these compounds.

Estrenes↗
PubMed1975

Proton magnetic resonance studies of peroxidases from turnip and horseradish.

Proton NMR spectra at 270 MHz have been measured for horseradish peroxidase and turnip peroxidase isoenzymes (P1, P2, P3 and P7) in both their high spin ferric native states and as the low spin ferric cyanide complexes. Resonances of amino acids near the heme have been identified and used to investigate variations in the structure of the heme crevice amongst the enzymes. Ligand proton resonances have been resolved in spectra of the cyanide complexes of the peroxidases and these provide information on the heme electronic structure. The electronic structure of the heme and the tertiary structure of the heme crevice are essentially the same in the acidic turnip isoenzymes, P1, P2 and, to a lesser extent, P3 but differ in the basic turnip enzyme, P7. The heme electronic structure and nature of the iron ligands in peroxidases are discussed. Further evidence is presented for histidine as the proximal ligand. A heme-linked ionizable group with a pK of 6.5 has been detected by NMR in the cyanide complex of horseradish peroxidase.

Binding Sites↗
PubMed1978

Nucleosome structure.

Electron microscopic and biochemical results are presented supporting the following conclusions: (1) Two molecules of each histone H2A, H2B, H3 and H4 are necessary and sufficient to form a nucleosome with a diameter of 12.5 +/- 1 nm and containing about 200 base pairs of DNA. (2) H3 plus H4 alone can compact 129 +/- 8 DNA base pairs into a sub-nucleosomal particle with a diameter of 8 +/- 1 nm. In such a particle the DNA duplex is under a constraint equivalent to negative superhelicity. (3) Chromatin should be viewed as a dynamic structure, oscillating between a compact structure (the nucleosome) and more open structures, depending on the environmental conditions.

Animals↗
PubMed1978

Differentiation of progressive versus regressive Rous virus-induced avian sarcomas according to tumor and infiltrating lymphocyte fine structure.

Electron microscope examination of progressing and regressing Rous virus-induced sarcomas in an inbred line of White Leghorns revealed that regressing tumors contained moderate to marked lymphocyte infiltration, frequent contact between lymphocytes and tumor cells, and extensive areas of necrosis. Lymphocytes infiltrating regressing tumors exhibited a polar accumulation of organelles at the point of contact between lymphocyte and target cell. On the other hand, progressing tumors contained low to moderate numbers of lymphocytes, infrequent lymphocyte-tumor cell interaction and less evidence of tumor cell degeneration. Lymphocytes from progressing tumors lacked the polar organization of organelles. This experimental system is offered as a means of studying the role of lymphocytes in tumor regression.

Animals↗
PubMed1979

A mammary gland whole mount technique that preserves cell fine structure for electron miscroscopy.

A mammary gland whole mount technique has been developed that preserves cell fine structure and makes it possible to also examine the preparations by electron microscopy. The glands are placed on glass microscope slides, fixed in a paraformaldehyde-glutaraldehyde mixture, defatted in acetone, stained with 0.5% methylene blue (or trypan blue) in saline, and dehydrated in ethanol. They are evaluated and photographed in 100% ethanol. Then specific areas (i.e. containing small growths, tumors, or other lesions) are selected, excised and prepared for electroscopy. The ultrastructural preservation is good, organelles are evident and there is no observable dye precipitate. The only unusual finding is that cell membranes display a "negative" image.

Animals↗
PubMedDate not supplied

[Electron microscopic structure of the Oidium, Oospora fragrans, a producer of lipase].

The fungus Oospora fragrans Berkh. was studied by electron microscopy. Both aerial and submerged oidia were found to be formed by division (septation) of mycelial hyphae in the course of growth. The ultrastructure of the aerial and submerged oidia was identical as was established by the techniques of ultratomy and freezing-etching. The latter technique revealed a certain difference in the morphology of the cytoplasmic membrane of these cells. The oidia of this fungus (arthrospores) differed in their structure from the arthrospores of actinomycetes.

Freeze Etching↗
PubMed2022

Preparation of Nucleosome Core Particles Complexed with DNA Repair Factors for Cryo-Electron Microscopy Structural Determination.

DNA repair in the context of chromatin is poorly understood. Biochemical studies using nucleosome core particles, the fundamental repeating unit of chromatin, show most DNA repair enzymes remove DNA damage at reduced rates as compared to free DNA. The molecular details on how base excision repair (BER) enzymes recognize and remove DNA damage in nucleosomes have not been elucidated. However, biochemical BER data of nucleosomal substrates suggest the nucleosome presents different structural barriers dependent on the location of the DNA lesion and the enzyme. This indicates the mechanisms employed by these enzymes to remove DNA damage in free DNA may be different than those employed in nucleosomes. Given that the majority of genomic DNA is assembled into nucleosomes, structural information of these complexes is needed. To date, the scientific community lacks detailed protocols to perform technically feasible structural studies of these complexes. Here, we provide two methods to prepare a complex of two genetically fused BER enzymes (Polymerase β and AP Endonuclease1) bound to a single-nucleotide gap near the entry-exit of the nucleosome for cryo-electron microscopy (cryo-EM) structural determination. Both methods of sample preparation are compatible for vitrifying quality grids via plunge freezing. This protocol can be used as a starting point to prepare other nucleosomal complexes with different BER factors, pioneer transcription factors, and chromatin-modifying enzymes.

Chromatin↗
PubMedDate not supplied

[Electron microscopic structure of the mycelium of Actinomyces chrysomallus, the producer of the antibiotic chrysomallin, during the stab fermentation process].

Ultrastructural changes in the mycelium of Actinomyces (Streptomyces) chrysomallus 2703 producing the antibiotic chrysomallin in the process of submerged fermentation are described. When the antibiotic was produced at a high rate, most hyphae remained viable for a long period of time and had the ultrastructure typical of the young cells of actinomycetes. At the same time, a number of degenerative changes due to aging were observed; these resulted in autolysis. A decrease in the antibiotic titre was accompanied with intensive sporulation in a considerable number of the submerged hyphae. Structural changes in the sporeforming hyphae distinctly differed from those in the vegetative ones: the cell walls became thicker and numerous septa were formed. The exogenous formation of submerged spores in the culture under study has been studied in detail for the first time.

Culture Media↗
PubMed1979

Light- and electron-microscopic structure of cells protruding into the mesencephalic ventricle of Scyllium stellare (Elasmobranchii, Selachii).

In the elasmobranch fish, Scyllium stellare, a complex group of cells protrudes into the cavity of the mesencephalic ventricle of the optic tectum. It consists of six to seven large spherical perikarya which resemble neurons of the mesencephalic nucleus of the Vth cranial nerve. The bundled processes of these cells form a stalk connecting the protrusion with the brain tissue. The protrusion is located in the region where the mesencephalic ventricle joins the cerebral aqueduct. This complex was not found in all specimens examined in the present study. The functional role of this peculiar group of cells, which contain dense core granules and are bathed in the cerebrospinal fluid, is open to discussion.

Animals↗