Decrease In Ionic Strength Research Articles

The interaction of nucleic acids with diamines

1. 1. The interaction of nucleic acids with aliphatic diaminns (H 2N(CH 2) nNH 2; 2≦ n≦10) has been investigated, largely by means of helix → coil transition (absorbancy-temperature) profiles. In general the most pronounced effects effects produced by amines were those on T m , the transition midpoint, which is increased (rise ≡ ΔT m ) in the presence of diamines depending on the following parameters. (a) The ionic strength: for any one DNA and amine a decrease in ionic strength leads to an increase in ΔT m and in the strength of the interaction. (b) The concentration of amine: a typical saturation behavior is observed with ΔT m proportional to the amine concentration at low values of the latter and reaching a limiting value ΔT m (max.) at high concentration. Half saturation with diaminopentane is reached at 10 −2 M amine at high, and 10 −4 M amine at low ionic strength. (c) The chain length of amine: the effect is optimal when n = 5 and decreases on either side of the optimum. (d) The conformation of the nucleic acid: the effect is exhibited by double-stranded DNA but not by RNA or single-stranded DNA, nor by “acid” polyadenylic acid. (e) The base composition of the DNA: ΔT m is related to mole % (adenine plus thymine) or, more rigorously, proportional to T m of the DNA used. Teh proportioonality constants are −0.13 and −0.47° per degree in high- and low-ionic-strength media, respectively. 2. 2. These observations have been interpreted in terms of a model which postulates m independent binding sites for diamines on a DNA helix, where m ⪡ total number of nucleotide pairs. These sites involve bridging between the phhosphate residues of one strand and the adenine and/or thymine residues of the other, with the most stable interaction occuring for n = 5.

Polyelectrolyte expansion of a lignin sulfonate microgel

The polyelectrolyte expansion of selected fractions of sodium lignin sulfonate has been measured viscometrically and by light scattering. Isoionic dilution techniques were used. The light-scattering radius of gyration, S ̄ , and the intrinsic viscosity, [η], increased with decrease in ionic strength I E and with S ̄ proportional to [η] 1 8 . These results supported a microgel model for the macromolecule. The increase of [η] with decrease in I E was not in quantitative accord with the theories of Flory or with those of Hermans and Overbeek. A new theory was developed in which the molecule was assumed to have free charges only on the surface. The elastic energy of the expanding network was equated to the electrostatic energy in the double layer. The resulting equation was found to apply to the first part of the expansion, but at very low values of I E the expansion was less than predicted theoretically.

Sodium chondroitin sulfate-protein complexes of cartilage. I. Molecular weight and shape

1. 1. Sodium chondroitin sulfate (SCS)-protein complexes of hyaline cartilage contain protein markedly different in amino acid composition from that of collagen. 2. 2. Light-scattering and viscosity data support the existence of a rodlike basic molecular unit. The molecular weight is 4.0 × 10 6, the length is 3700 A., the linear density is about 1000 avog./A. The structure proposed conceives the protein moiety as a core 3700 A. in length along which are distributed about 62 units of SCS, each of 50,000 molecular weight. Each linear SCS molecule, attached by one or more bonds to the protein core, retains its flexibility which allows an increase in average lateral chain extension with decrease in ionic strength. 3. 3. Aggregates, which have molecular weights as great as 50 × 10 6, are possibly formed by both lateral and end-to-end, hydrogen-bonded association of basic units. Additional protein may also be involved. 4. 4. The physiological significance of the results is discussed.

Electrophoretic Studies of Tobacco Mosaic Virus

Abstract The variations of the mobility of tobacco mosaic virus (TMV) in phosphate buffer at pH 7.7 with changes in concentration and ionic strength have been investigated. The mobility is essentially independent of the concentration and has an average value of −7.05×10−5cm2/sec. volt in the phosphate buffer of ionic strength 0.2. On the other hand, the mobility increases greatly with the decrease of ionic strength. The net charge on the TMV particle, calculated from the mobility data by the aid of Gorin’s equation, was found to be constant (about −1,800) all over the range of ionic strength examined. Although it is considerably lower than the theoretical valency calculated from the analytical data, this low value of the valency from the mobility is quite reasonable to explain the observation that there is no serious, divergence from the ideal behaviour in the electrophoresis of TMV solution.

Reversible association processes of globular proteins. I. Insulin

1. 1. The dissociation of insulin is favored by ( a) an increase in charge, ( b) a decrease in ionic strength, and ( c) an increase in temperature. 2. 2. The dissociation curves may be fitted best with stepwise constants. 3. 3. The heat of dissociation falls with increase of charge. 4. 4. Evidence is presented for the presence of aggregates as high as the pentamer.