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B J Stevens

Publications and source records attributed to B J Stevens.

At least 55 records · Page 3Linked to original sources
PubMed1975

[Analysis of ribosomes by polyacrylamide gel electrophoresis (author's transl)].

Ribosomal polymers, monomers and subunits from several eukaryotes and prokaryotes were isolated and analyzed by polyacrylamide gel electrophoresis. Extraction of RNA from ribosomal particles after their migration in a polyacrylamide gel, analyses by sedimentation in sucrose gradients and observations in the electron microscope were carried out in parallel. Attention was directed to the reproducibility, the precision and the limitations of the electrophoresis technique.

Animals↗
PubMed1975

Effecting change.

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PubMed1974

Mitochondrial and cytoplasmic ribosomes from Tetrahymena pyriformis. Correlative analysis by gel electrophoresis and electron microscopy.

Mitochondrial and cytoplasmic ribosomes from Tetrahymena pyriformis have been isolated and studied by the techniques of polyacrylamide gel electrophoresis and electron microscopy used in conjunction. Although the two ribosome types show the same coefficient of sedimentation (80S) in sucrose gradients, they can be distinguished by gel electrophoresis: mitoribosomes migrate in a single band, considerably slower than the cytoribosome band. Electron microscope observations of negatively stained cytoribosomes show typical rounded or triangular profiles, about 275 x 230 A; mitoribosome profiles are much larger and clearly elongate, about 370 x 240 A. An electron-opaque spot delimits two nearly equal size subunits. In mixtures of mito- and cytoribosomes, each type can be recognized by its characteristic electrophoretic mobility and by its distinctive fine structure. Cytoribosomal 60S and 40S subunits each produce a distinct electrophoretic band. On the contrary, neither electrophoretic analysis, using a variety of conditions, nor electron microscopy is able to discern two different subunit types in the single 55S mitoribosomal subunit peak. Electrophoretic analysis of RNA shows that both ribosomal RNA species are present in the mitoribosomal subunit fraction. These results establish that mitoribosomes from T. pyriformis dissociate into two subunits endowed with the same sedimentation coefficient, the same electrophoretic mobility, and a similar morphology.

Animals↗
PubMed1973

Menkes' kinky hair disease: further definition of the defect in copper transport.

Duodenal mucosa obtained from two patients with Menkes' syndrome contained abnormally large amounts of copper. The defect in copper absorption in this disease must lie in the process of intracellular handling or of transport across the serosal cell membrane. Fibroblastic cells cultured from the skin of patients and of heterozygous females show intense metachromasia in primary culture which disappears in subculture. These cells may be useful for the study of copper transport in vitro and for the identification of heterozygotes in affected families.

Biological Transport↗
PubMed1972

Mitoribosomes from Candida utilis. Morphological, physical, and chemical characterization of the monomer form and of its subunits.

Highly purified mitochondrial ribosomes (mitoribosomes) have been obtained from the yeast Candida utilis. Sedimentation analysis in sucrose gradients made in 5 mM MgCl(2), 1 mM Tris, pH 7.4 and 50 mM KCl clearly distinguishes mitoribosomes (72S) from cytoplasmic ribosomes (cytoribosomes) (78S). Mitoribosomes are completely dissociated into 50S and 36S subunits at 10(-4)M MgCl(2) whereas complete dissociation of cytoribosomes into 61S and 37S subunits occurs only at 10(-6)M MgCl(2) Electron microscopy of negatively stained mitoribosomes (72S peak) shows bipartite profiles, about 265 x 210 x 200 A Characteristic views are interpreted as frontal, dorsal, and lateral projections of the particles, the latter is observed in two enantiomorphic forms Mitoribosome 50S subunits display rounded profiles bearing a conspicuous knoblike projection, reminiscent of the large bacterial subunit. The 36S subunits show a variety of angular profiles. Mitoribosomal subunits are subject to artifactual dimerization at high Mg(2+) concentration Under these conditions, a supplementary 80S peak arises. Electron microscopic observation of the 80S peak reveals closely paired particles of the 50S type Buoyant density determinations after glutaraldehyde fixation show a single peak at rho = 1.48 for mitoribosomes and 1.53 for cytoribosomes In the presence of ethylenediaminetetraacetate (EDTA), two species of RNA, 21S and 16S, are obtained from mitoribosomes, while 25S and 17S RNA are obtained from cytoribosomes It is established that the small and large RNA species are derived from the 36S and 50S subunits, respectively, by extraction of the RNA from each subunit The G + C content of the RNA is lower for mitoribosomes (33%) than for cytoribosomes (50%). Incubation of C utilis mitochondria with leucine-(14)C results in the labeling of 72S mitoribosomes. The leucine-(14)C incorporation is inhibited by chloramphenicol and resistant to cycloheximide Puromycin strips the incorporated radioactivity from the 72S mitoribosomes, which is consistent with the view that leucine-(14)C is incorporated into nascent polypeptide chains at the level of mitoribosomes

Adenine↗