Weak Electrostatic Forces Research Articles

Characteristics of a bacteriophage T4-induced complex synthesizing deoxyribonucleotides.

A preparation of bacteriophage T4-induced deoxyribonucleotide synthetase complex is described. This very large complex of enzymes can be separated by centrifugation at 100,000 X g, by sucrose step gradient centrifugation, or with molecular exclusion columns. By direct assay and by unidimensional and two-dimensional acrylamide electrophoretic separations the following T4-coded enzymes were shown to be associated with the complex: ribonucleoside diphosphate reductase, dCMP deaminase, dCTP/dUTPase, dCMP hydroxymethylase, dTMP synthetase, and DNA polymerase. Other phage-coded prereplicative proteins related to DNA replication and other phage functions such as the proteins coded by genes 32, 46, rIIA, and rIIB as well as many unidentified proteins were also consistently associated with the isolated fractions. T4 DNA topoisomerase, a membrane-bound enzyme, was found in quantity in all purified fractions of the complex, even in preparations apparently free of membrane and of T4 DNA. The functional integrity of a segment of the complex was followed by measuring the conversion of [5-3H]CDP to the level of 5-hydroxymethyl dCMP. This series of reactions requires the actions of T4-coded ribonucleoside diphosphate reductase and its associated reducing system, dCTP/dUTPase and dCMP hydroxymethylase, 3H being lost to water at the last step. In this reaction sequence an intermediate, [5-3H]dCMP, is maintained at low steady state concentrations, and argument is presented that the synthesis of deoxyribonucleotides is channeled and normally tightly coupled to DNA replication. One of the primary characteristics of this complex is its ready dissociation of dilution into smaller complexes of proteins and to the free forms of the proteins. That the complex is held together by weak electrostatic forces was supported by its sensitivity to dissociation at moderate salt concentrations. Not only the enzymes required in deoxyribonucleotide synthesis but T4 DNA polymerase, T4 DNA topoisomerase, and a number of other proteins dissociate to varying degrees from the larger complexes under these conditions.

Capture of aerosols on a sphere in the presence of weak electrostatic forces

Capture of aerosols on a sphere in the presence of weak electrostatic forces

Thermodynamic study of the 1 : 1 solid compound, hexafluorobenzene–benzene

A study of the 1 : 1 solid compound hexafluorobenzene–benzene using a differential scanning calorimeter has enabled an estimate to be made of the enthalpy of formation of the compound when it is formed from the two pure solids. The measured value, + 1.0 ± 0.3 kJ mol–1, is small and positive and is good evidence that the compound is stabilized by preferred geometrical packing effects probably enhanced by weak electrostatic forces rather than by any of the normal specific intermolecular interactions of the charge transfer type. A solid–solid transition was detected at 249.2 K. This is thought to be a genuine order–disorder transition brought about by a partial disordering of the regular alternate packing sequence observed at lower temperatures.

Interaction in vitro des acides nucléiques avec des alcaloïdes extraits de Vinca rosea et l'acide glutamique

Summary The vinca alcaloids and glutamic acid react with nucleic acids and cause a decrease of their Tm. Glutamic acid binds to DNA and poly (A) poly (U) and cosediments with these macromolecules in a sucrose gradient. The binding is probably due to weak electrostatic forces as the bonds are very sensitive to modifications of ionic strength.