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Biomedical subjects

B Hartmann

Publications and source records attributed to B Hartmann.

At least 199 records · Page 11Linked to original sources
PubMed1983

Spectroscopic studies of (m5dC-dG)3: thermal stability of B- and Z-forms.

The hexanucleoside pentaphosphate d(m5CpGpm5CpGpm5CpG) has been studied in solution by ultra-violet absorption, circular dichroism and 31P nuclear magnetic resonance under various experimental conditions. In 0.2 M NaClO4 at low temperature, an hexamer duplex is formed which has a B or B-like conformation. As the salt concentration is increased, a transition from a B-form to the Z-form occurs and is complete in 3 M NaClO4. In 3 M NaClO4, the behavior of the Z double helix is complex as a function of temperature. The variation of the circular dichroism at 295 nm is biphasic. A first transition occurs over a large range of temperature and corresponds to a conformational change due to a non-cooperative intramolecular process. Ultra-violet absorption and 31P nuclear magnetic resonance show that the new conformation arising from a distortion of the backbone is not similar to that observed in low salt conditions (B-form). At high hexanucleotide concentration, aggregates are formed. The second transition is cooperative and corresponds to the melting of a double stranded helix into single strands.

Circular Dichroism↗
PubMed1982

The B reversible Z transition of poly(dI-br5dC).poly(dI-br5dC). A quantitative description of the Z form dynamic structure.

The study of poly(dI-br5dC).poly(dI-br5dC) films by infrared spectroscopy shows that in low salt concentration, the conformation of this polynucleotide belongs to the B-family and in high salt concentration to the Z-family. 31P nuclear magnetic resonance and circular dichroism confirm the existence of these two forms. By circular dichroism and ultraviolet absorption, it is shown that the equilibrium constant of the B reversible Z transition depends upon temperature. The deuteration rates of exchangeable protons involved in hydrogen bonds between base pairs were deduced from the changes in absorbance near 1700 cm-1. In the B-form, one class of protons is measured with an exchange half-time of 20 minutes. In the Z-form, two classes of protons are measured with very different exchange half-times, the exchange half-time of the slow protons being of the order of 850 minutes. By comparison of these results with those previously obtained for poly(dG-dC).poly(dG-dC), these very slow protons of these two Z-polynucleotides are identified as the cytosine amino protons. A quantitative description of the dynamic structure of the Z-form is presented.

Circular Dichroism↗
PubMed1981

The B goes to Z transition of poly(dG-dC) . poly(dG-dC) modified by some platinum derivatives.

Poly(dG-dC) . poly(dG-dC) was modified by chlorodiethylenetriamino platinum (II) chloride, cis-dichlorodiammine platinum (II) and trans-dichlorodiammine platinum (II), respectively. The conformation of these modified poly(dG-dC) . poly(dG-dC) was studied by circular dichroism. In 4 M Na+, the circular dichroism spectra of poly(dG-dC)dien-Pt (0 less than or equal to rb less than or equal to 0.2) are similar (rb is the amount of bound platinum per base). It is concluded that the conformation of these polymers belongs to the Z-family. Dien-Pt complexes stabilize the Z-form. The midpoint of the Z goes to B transition of poly(dG-dC)dien-Pt(0.12) is at 0.2 M NaCl. Moreover another B goes to Z transition is observed at lower salt concentration (midpoint at 6 mM NaCl). In 1 mM phosphate buffer, the stability of Z-poly(dG-dC)dien-Pt(0.12) is greatly affected by the presence of small amounts of EDTA. Poly(dG-dC) . poly(dG-dC) modified by cis-Pt and trans-Pt complexes do not adopt the Z-form even in high salt concentration.

Circular Dichroism↗
PubMed1981

Synthesis and structural studies of a self-complementary decadeoxynucleotide d(AATTGCAATT). I.-Synthesis and chemical characterization of the decanucleotide.

The synthesis of the self-complementary decadeoxynucleotide d(AATTGCAATT) is described. The phosphotriester method has been used with several modifications. Protected nucleotides have been prepared in a one-step reaction involving a new monofunctional phosphorylating agent: p-chlorophenyl-beta-cyanoethyl phosphate. Triethylammonium salts of mononucleoside 3'-phosphodiesters were obtained either by decyanoethylation of the triesters or, in the case of thymine, by a one-step reaction starting from 5'-0-methoxytritylthymidine and the mixture pyridine-para-chlorophenyl-methyl-phosphorobromidate. The usual coupling reactions were then used to prepare the decadeoxynucleotide in large quantities.

Chemical Phenomena↗
PubMed1981

Immunochemical studies of DNA modified by cis-dichlorodiammineplatinum(II) in vivo and in vitro.

Two rabbits were immunized with native DNA modified in vitro by cis-dichlorodiammineplatinum(II) (cis-Pt). The interactions between the antiserum and several natural and synthetic nucleic acids were studied primarily by radioimmunoassays. Native DNA's modified by platinum compounds with labile groups in the cis position are recognized by the antiserum. No cross-reaction is found with native DNA's substituted by other platinum compounds [trans-dichlorodiammineplatinum(II), cis-diamminotetrachloroplatinum(IV), and chlorodiethylenetriamminoplatinum(II)] and with natural and synthetic modified polyribonucleotides. cis-Pt-modified oligodeoxyribonucleotides and enzymatically hydrolyzed cis-Pt-modified native DNA do not bind to the antiserum. cis-Pt-modified double-stranded synthetic polydeoxyribonucleotides are either hardly recognized or not recognized at all. The antiserum recognized a modified double-stranded helix in DNA which is not formed in several modified synthetic DNA's and RNA's. At least two different antigenic determinants are present in cis-Pt-modified DNA at a ratio of cis-Pt to bases equal to 0.05. Finally, the antiserum does not react with in vivo cis-Pt-modified DNA.

Animals↗
PubMed1978

Conservation of active ribosomes in acetone-treated cells of Tetrahymena pyriformis.

The preparation of an acetone powder of cells of Tetrahymena pyriformis GL is described. A comparison of ribosomal particles isolated from acetone-treated and untreated cells shows that structurally and functionally intact ribosomes can be isolated from acetone-treated cells. Fully active ribosomes have been isolated from acetone powder of Tetrahymena that had been stored for more than 6 months at 4 degrees C. Thus, this procedure allows easy storage of large quantities of cells for the bulk preparation of active ribosomes.

Acetone↗