Search PubMed⌕ Search

Biomedical subjects

K Weber

Publications and source records attributed to K Weber.

At least 721 records · Page 40Linked to original sources
PubMed1977

[Disturbances in time perception in relation to changes in experiencing music in experimental psychosis].

Music is a structure ('Gestalt') in time. The recognition of disturbances of the perception of music enhances the knowledge of disorders of perception of time. Disturbances of perception of music and time in experimental psychoses (psilocybine) are discussed in relation to the studies by Piaget on the development of the notion of time in childhood. The results allow a new interpretation of the disturbances of the perception of time in diencephalic disorders as described in the literature.

Adult↗
PubMed1976

Thermodynamic studies on the specificity of L-isoleucine-tRNA ligase of Escherichia coli MRE 600. Calorimetric investigations on binding of amino acids and isoleucinol to the enzyme.

The association enthalpies, delta Ha, involved in the reactions between L-isoleucine:tRNA ligase (AMP-forming) from Escherichia coli MRE 600 (EC 6.1.1.5) and various amino acids have been determined calorimetrically in 50 mM potassium phosphate buffer, at pH 7.5, in the presence of 1 mM dithioerythritol. The delta Ha values for binding of L-isoleucine, L-leucine, L-valine, L-norvaline and L-2-amino-3S, 4-dimethyl pentanoic acid agree within the limits of experimental error in magnitude (3.7 +/- 0.9 kcal mol-1 or 15.5 +/- 3.8 kJ mol-1 at 25 degrees C) and variation with temperature (delta cp = -430 +/- 20 cal mol-1 K-1 or 1799 +/- 84 J mol-1 K-1). In view of the large differences in the equilibrium constants for the corresponding binding equilibria, the identical association enthalpies suggest that the enthalpic contribution to the Gibbs free energy of binding, delta Ga, cannot be responsible for the specificity of the interaction of the enzyme with the amino acids. It has rather to be inferred that the entropic term, delta Sa, is decisive in discriminating the correct amino acid. Analogous calorimetric binding studies on the reaction between L-isoleucinol and the enzyme suggest that the absence of the carboxyl group renders the association enthalpy more positive (by 4-5 kcal mol-1 or 16.7-20.9 kJ mol-1) with respect to that of the amino acids. The variation with temperature of the delta Ha values, however, practically parallels that of the amino acids.

Amino Acids↗
PubMed1976

Limited proteolytic digestion of lac repressor by trypsin. Chemical nature of the resulting trypsin-resistant core.

Tryptic digestion of Escherichia coli lac repressor under nondenaturing conditions readily removes 59 amino acids from the NH2-terminal end of the polypeptide chain. Longer digestion removes an additional 20 or more amino acids from the COOH terminus, leaving a highly trypsin-resistanct core molecule. The lac repressor tetrameric structure and inducer-binding activity are retained by the tryptic core. Operator-binding activity, however, is lost as the NH2-terminal end is degraded. Many or all of the possible trypsin cleavage sites in the NH2-terminal region are available to attack by the enzyme, indicating that this part of the polypeptide chain is exposed to the environment. Lac repressor, missing the NH2-terminal end, renatures efficiently from random-coil solvent to tetramers with full inducer-binding activity, indicating that the NH2-terminal region is not necessary for the appropriate three-dimensional folding of the polypeptide chains. Core which lacks both the NH2 and COOH termini renatures to tetramers with low efficiency.

Amino Acid Sequence↗
PubMed1976

Immunochemical analysis of the functions of the subunits of phage Qbeta ribonucleic acid replicase.

We have prepared rabbit gamma-globulins specifically directed against each of the bacterial host proteins required for the in vitro replication of RNA phage Qbeta RNA: the protein synthesis elongation factors EF-Tu and EF-Ts, the 30 S ribosomal protein S1, and the Qbeta "host factor". We have used these antibodies as specific probes to study the roles that these polypeptides play in the in vitro replication of Qbeta RNA by the Qbeta replicase as well as the poly(C)-directed synthesis of poly(G) by this enzyme. The poly(C)-directed reaction is much less sensitive to antibody inhibition than is the Qbeta RNA-directed reaction.

Animals↗
PubMed1976

The relationship between group C adenovirus tumor antigen and the adenovirus single-strand DNA-binding protein.

The group C adenoviruses code for a single-strand specific DNA-binding protein of molecular weight 72,000 daltons which is synthesized at early times after productive viral infection. Experiments were designed to determine whether this single-strand specific DNA-binding protein was expressed in adenovirus tumors and transformed cells. Two independently derived preparations of anti-sera from hamsters bearing group C adenovirus tumors were tested for antibody against the single-stranded DNA-binding proteins. One antiserum contained antibodies that reacted with these DNA-binding proteins, while the second antiserum did not contain detectable levels of antibody. Five adenovirus type 2 transformed rat cell lines were tested for the presence of the single-stranded specific DNA-binding proteins. Two of the five transformed cells expressed detectable levels of this protein. These results indicate that the group C adenovirus single-strand specific DNA-binding proteins are expressed in some, but not all, adenovirus tumors and transformed cell lines. Those transformed cell lines (type 2) containing a portion of the adenovirus genome designated by the Eco R-I-B restriction enzyme fragment express the single-strand specific DNA-binding proteins. Those cell lines missing this Eco R-I-B fragment do not contain this viral protein. Other experiments have located the structural gene of the signle-strand specific DNA-binding protein in the Eco-R-I-B DNA fragment, indicating that when this gene is present in a transformed cell, it is expressed.

Adenoviridae↗
PubMed1976

Cytoplasmic microtubules in tissue culture cells appear to grow from an organizing structure towards the plasma membrane.

A structure which appears to organize cytoplasmic microtubules in interphase mouse 3T3 cells can be visualized by immunofluorescence microscopy. Purified monospecific antibody against homogeneous tubulin from brain visualizes, in addition to cytoplasmic microtubules, a cytoplasmic polar structure as the focal point from which the microtubules seem to radiate. The structure is preserved after treatments that depolymerize cytoplasmic microtubules, i.e., exposure of cells to mitotic drugs or to low temperature. When cells recover from these treatments one end of each microtubule organizing structure acts as a nucleating center from which cytoplasmic microtubules grow toward the plasma membrane. Thus cytoplasmic microtubules assemble in vivo in an ordered unidirectional manner, and therefore the cell must be able to avoid the assembly of unwanted, unoriented, and disconnected microtubules. These results suggest that the assembly of tubulin into microtubules is regulated in vivo.

Cell Line↗
PubMed1976

Isolation of a set of hybrid lac repressors made in vitro between normal lac repressor and its homogeneous tryptic core.

Lactose repressor can be renatured from 8 M guanidine-HCl solution. The renatured repressor is tetrameric and shows DNA binding activity. Thus it becomes possible to obtain hybrid tetramers in vitro between normal repressor and repressor defective in DNA binding by simultaneous denaturation and renaturation. In order to facilitate the separation of the different hybrids, we have used a lac repressor derivative that does not bind DNA, which is missing the amino-terminal 59 residues of the polypeptide chain (homogeneous tryptic core). The hybrids resulting from the mixed renaturation of homogeneous tryptic core and normal repressor can be separated by electrophoresis on Cellogel. The hybrids have been recovered, and a preliminary characterization of their DNA-binding properties is reported.

Bacterial Proteins↗