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Biomedical subjects

B Wolf

Publications and source records attributed to B Wolf.

At least 379 records · Page 21Linked to original sources
PubMed1976

New low resolution model for 50S subunit of Escherichia coli ribosomes.

Neutron low angle scattering studies of the 50S subunit of E. coli ribosomes with the contrast variation method reveals large fluctuations in the scattering density. A region of relatively low scattering density, rich in proteins, surrounds an RNA-rich core of higher scattering density. The centers of mass of the RNA and protein parts of the 50S subunit are separated by a distance (20 A) that is considerably smaller than that reported in previous studies.

Escherichia coli↗
PubMed1976

Ligament length patterns, strength, and rotational axes of the knee joint.

Using intact fresh specimens, the cruciate ligament lengths for positions of flexion and internal-external rotation were computed using a non-invasive technique; using photographic methods, the centers of transverse rotation on the tibia and the direction of the flexion axis were also obtained. The anterior cruciate was found to be particularly effective in restraining internal tibial rotation; the ability of the posterior cruciate to restrain external rotation, however, depended strongly on the transverse axis location. Ligament length changes during flexion were found to be small in the absence of rotary torque and anteroposterior forces. The average internal rotation occurring during flexion was 37 degrees, half of which took place during the first 15 degrees of flexion. Ultimate rupture strengths of approximately 60 kh for the cruciates were measured, with stiffnesses of 16 kg/mm.

Adult↗
PubMed1976

[A simple opto-electronic device for morphometry of electron micrographs (author's transl)].

Morphometric investigations of light or electron microscopic photographs can be both time consuming and tedious when statistical results are to be obtained. Therefore, an opto-electrical morphometer has been developed to facilitate such investigations. The photograph is placed in between a light source and a grid, and the shape of the object in question is outlined with an electronic pencil. The impulses so produced can be converted into counts which may than be fed into a pocket-sized calculator or micro-computer for further analyses.

Cytological Techniques↗
PubMed1976

Rosette plaques with lymphoid cells from heterozygous rabbits. Ani-hapten antibody-forming cells displaying either one or both b locus surface allelic markers.

A rosette-plaque model was employed to test for the expression of b locus allelic markers at the surface of lymph node lymphocytes (LNL) from heterozygous (b4,6) rabbits, 5 days after immunization with NIP-diphtheria toxoid. Before immunization, in all animals examined, LNL displaying both b4 and b6 determinants at the surface (range 5-20 per cent) were detected, the remainder consisting of cells exhibiting only one or the other determinant. After immunization, five of the thirteen heterozygotes apparently had gone into allelic exclusion as LNL from these animals showed only b4 or b6 rosettes which secreted anti-NIP antibody in the plaque. The eight remaining rabbits remained in allelic inclusion. Since cytophilic uptake of allotype might have contributed to double expression, LNL from immunized animals were treated with pronase to remove surface immunoglobulin. When the stripped cells were cultured overnight in serum-free medium, reappearance of b4, b6, and b4 plus b6 expressing cells was seen. When pronase-stripped cells were incubated in cycloheximide (20 mug/ml) for 5 hr, no allotype synthesis was found but inhibition was relieved when the cells were washed free of the antibiotic. Regrowth resulted in rosette levels similar to those found originally in the three allotype-bearing populations. Stripping the cell surface allotype with pronase, and allowing regrowth of allotype overnight also resulted in one of four animals regaining the ability to express both allotypes at the surface in the plaque-forming situation. Lymphocytes from homozygous controls (b4,4 and b6,6) displayed their own individual allelic markers either when the cells from each were tested alone or in combination, unimmunized or immunized. An additional finding was the apparent lack of allelic preference for NIP in the heterozygotes as approximately similar numbers of cells were found bearing the b4 and b6 marker at the surface in the NIP plaque.

Alleles↗
PubMed1975

Structural transitions of deoxyribonucleic acid in aqueous electrolyte solutions. I. Reference spectra of conformational limits.

The circular dichroism properties of calf thymus DNA have been examined at 27 degrees over the wavelength range of 215-300 nm in aqueous solutions of NaCl, KCl, LiCl, CsCl, and NH4Cl at pH 7. The concentrations of these electrolytes were varied from 0.01 to ca. 5-10 m. The spectral changes induced by changes in concentration of NaCl and KCl and all but the highest concentrations of NH4Cl as well as lower concentrations of Cstcl and LiCl could be represented by a common two-state transition involving the conversion of the typical conservative spectrum commonly seen in dilute solutions of these salts to a nonconservative spectrum similar to that obtained by Tunis-Schneider and Maestre ((1970), J. Mol. Biol. 52, 521) for the C form of DNA. At higher concentrations of CsCl, LiCl, and NH4Cl, an additional component, resembling an A type spectrum, was required to account for the observed CD changes with changing concentration of electrolyte. Relying on the published spectra of the B, the C, and the A forms of DNA by Tunis-Schneider and Maestre for identification and approximate values of the molecular ellipticities of these forms, we have analyzed these spectral transitions by two least mean squares methods in order to obtain accurate reference spectra of aqueous "B", C, and "A" conformations of calf thymus DNA. The results obtained suggest that although the C form in solution is identical with that obtained in film, the aqueous B conformational limit is not identical with the crystallographic Watson-Crick structure. In addition, the A form generated in solution under our experimental conditions appears to be more similar to that assumed by low molecular weight Escherichia coli DNA at 75% relative humidity rather than calf thymus DNA at the same relative humidity.

Animals↗
PubMed1975

Structural transitions of deoxyribonucleic acid in aqueous electrolyte solutions. II. The role of hydration.

The data and approach reported in paper I (Hanlon et al., 1975, preceding paper) have been used to calculate the fractional changes in secondary structure of calf thymus deoxyribonucleic acid which occur in aqueous solutions as a function of the concentration of NaCl, KCl, LiCl, CsCl, and NH4Cl. There is a continuous loss in the "B" character of the nucleic acid with concomitant production of the C and, in some instances, an A form, as well, as the salt concentration increases. Sedimentation velocity studies suggest that there is an accompanying change in the hydrodynamic characteristics of the DNA molecules, as well. Utilizing the existing hydration data in the literature (Hearst and Vinograd, 1961a,b; Hearst, 1965; Tunis and Hearst, 1968a; Cohen and Eisenberg, 1968; Falk et al., 1962, 1963a,b), we have found that a gradual loss of "B" character and a decrease in the frictional coefficient of DNA occur as the net hydration of DNA is reduced from the fully hydrated from (60-80 mol of H2O/mol of nucleotide) to values of ca. 12-14 mol of H2O/mol of nucleotide. Below that value, a more precipitous decrease in these properties occurs. Extrapolation of the linear relationship observed between the fractional B content and the net hydration in the latter regions yield values of ca. 18 mol of H2O/mol of nucleotide at 100% B and ca. 4 mol of H2O/mol of nucleotide at 0% B (i.e., 100% C or C + A) for the alkali metal salts of DNA. The ammonium salt retains somewhat more H2O in the C and A forms (ca. 7). These results together with the hydration site assignments of Falk et al. (1962, 1963a,b) are interpreted in terms of a hydration model for DNA in aqueous solution in which an intact primary hydration shell of ca. 18 mol of H2O/mol of nucleotide is required for the maintenance of the "B" conformation. Removal of all but those water molecules solvating the phosphate groups results in the conversion to the C forms, predominantly, with a small amount of A structure formed as well in some salts. The accompanying changes in the sedimentation coefficients suggest that the DNA molecule assumes a more compact and/or flexible form under these conditions in which it is mainly in the C and A structures. The combination of these two events which ensue upon dehydration create a polymeric structure which can be more easily packaged in biological systems.

Animals↗
PubMed1972

Mixed conformations of deoxyribonucleic acid in chromatin: a preliminary report.

We have established empirical limits for the circular dichroism spectra appropriate for aqueous solutions of the B, C, and A forms of calf-thymus DNA and have analyzed DNA conformations in biological structures. The circular dichroism spectrum above 250 nm of purified calf-thymus chromatin can be satisfactorily accounted for as a linear combination of contributions of the B and C reference spectra without invoking higher-order structures such as supercoils. The amount of A contribution, if any, is below the limit of detection (</=4%). The fraction of bases in the B conformation depends on the method of isolation of nucleohistone, and ranges from 30-50%. The B content of a given preparation is increased by addition of a chelating agent and decreased by addition of divalent ions. More radical increases ensue upon protein removal. Nuclease treatment results in a dramatic decrease in B content. The fraction of bases melting out in the lower transitions of the complex melting profile of a given chromatin preparation corresponds to its B content. We propose a model for chromatin structure in which part of the DNA duplex is exposed or accessible to the solvent and is in the B conformation. The remainder of the base pairs and ribophosphate backbone are protected from interaction with the solvent by efficient histone coverage and are in the C conformation. Divalent ions modulate the distribution of bases between these two conformations.

Animals↗
PubMed1972

The characteristics and genetic map location of a temperature sensitive DNA mutant of E. coli K12.

A temperature sensitive strain of E. coli K12 has been isolated in which residual DNA synthesis occurs at the 40 degrees C restrictive temperature; syntheses of RNA, protein and DNA precursors are not directly affected. The mutation has been designated dna-325 and is located at 89 min on the E. coli map in the same region where the dnaC locus is found. dnaC mutants are considered to be defective in DNA initiation. Some of the data are consistent with the view that the dna-325 mutation is temperature sensitive in the process of DNA initiation rather than DNA chain elongation: (1) more than two cell divisions occur after a shift to 40 degrees C; (2) upon a shift down to 30 degrees C, cell division occurs again only after the DNA content of the cells has doubled; (3) 80% more DNA is made at 30 degrees C in the presence of chloramphenicol after prior inhibition of DNA synthesis at 40 degrees C. These three observations indicate that rounds of DNA replication were completed at 40 degrees C. Also (4) infective lambda particles can be made at 40 degrees C long after bacterial DNA replication has ceased. It appears however that some DNA initiation can occur at 40 degrees C since (1) a limited amount of DNA synthesis does occur at 40 degrees C after prior alignment of the chromosomes by amino acid starvation at 30 degrees C, and (2) after incubation in bromouracil at the restrictive temperature, heavy DNA is found with both strands containing bromouracil.

Amino Acids↗