摘要:

AbstractInvestigations have been made on the optical rotatory dispersion properties ofE. coliribosomes and their constituent RNA and proteins. The results indicate that (1) no conformational changes are involved in the formation of a 70S particle from the 50S and 308 subunits, (2) theE. coliribosomal proteins are similar to most globular proteins with little α‐helix content, and (3) the conformation of RNA and proteins inside the ribosome is very similar to that in the free sta

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractThe iodine which is added to an aqueous amylose solution is bound only partly by the amylose while forming the blue complex and partly remains free. The equilibrium normality of the free and the bound iodine at half‐saturation of amylose by iodine is designated as [If]vand [Ib]w, respectively. The stability of the poly iodine chain formed within the axis of amylose helices depends on its length, i.e., indirectly on the DP of the amylose helices: the greater this stability, the lower the [If]vvalue. The amylose molecule consists of helical segments. Such a molecule may behave as a random coil. The average length of the helical segments in freshly prepared amylose‐iodine complexes depends on temperature, pH, iodide concentration, the presence of other complex‐forming agents, and the DP of the amylose. This latter factor is investigated in the present paper. By the aid of an automatically recording photometrictitrating device the coherent values of [Ib] and [If] were determined. Plotting these values againstDPnfor mechanochemically degraded as well as for periodateo‐xidized amyloses resulted in curves consisting of two linear sections. The break of the curves occurred betweenDPn110 and 130. It was concluded that belowDPn= 100 the DP of helical segments (=sDPn) is identical to theDPnof the total molecule, i.e., the molecule consists of only a single, relatively stiff helix. Above this limit the molecule contains several helical segments. TheDPof these helical segments can be calculated as follows:sDPn= 141.1 − 10.2 × 105[If]v. This equation is considered to be valid for 0.5–0.6 mg. amylose in 100 ml. 0.1NHCl at 20°C., λ = 650 mμ, euuvet diameter 3.4 cm., the feed rate of the iodate‐iodide titrating solution (in acid medium resulting in a 5 × 10−3NI2solution with a molar iodide to iodine ratio of 1.5) is 0.4ml./min. Amylose molecules of, e.g.,DPn= 1380 consist of an average of 11.4 segments having aDPof about 120 and consisting of an average of

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractThe equilibrium normality [If] of free iodine in amylose‐iodine complex formation is a function of the length of the polyiodine chains. This length depends on theDPof helical segments of amylose (sDPn). Values of [If] and of the concentration of the bound iodine [Ib] were determined by the continuous photometric titration with automatic recording. Plots of [Ib] versus [If] give an integral distribution curve. Since the relation between [If] andsDPnis known, the graphic differentiation of the [Ib] versus [lf] curve furnishes the differential distribution curve, representing the mass distribution of the helical segments according to theirDP. The peak of this curve is characteristic of the percentage and DP of those helical segments, which occur in the largest amount. On the basis of the differential distribution curve the polymolecularity of the investigated sample may be judged. The titration of amylose samples degraded by various methods gives different distribution curves. Titrating mixtures of samples with widely differing average DP values results in differential curves having more than one maximu

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractThe helix‐coil transition temperatureTcof poly(γ‐benzylL‐glutamate) in binary solvent mixtures of dichloroacetic acid and 1,4‐dichlorobutane, 1‐chlorooctane, or 1‐chlorododecane have been measured. A treatment is presented with which the transition enthalpy can be calculated from the observed dependence ofTcon solvent composition. Results are compared with previously obtained calorimetric data. The underlying assumptions of the calculation a

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractA marked molecular weight fractionation accompanies the demixing or phase separation resulting from the complex coacervation of mixtures of aqueous solutions of salt‐free isoionic unfractionated gelatins with pI's of 5 and 9. Viscosity studies show that the fractionation is such that the concentrated phase tends to maintain constant, homogeneous composition. A second feature, seen in phase volume and concentration measurements, is a marked self‐suppression of coacervation intensity with increasing mixing concentration. These data were interpreted in terms of a dilute‐phase aggregate model which assumes nearly equal electrostatic free energies of mixing in dilute aggregate and concentrated random phase. The driving force for phase separation is the entropy increase upon formation of the random phase but demixing also depends upon the polymer‐solvent interaction parameter χ, in the same fashion as in simple coacervation. The dilute‐phase aggregate model indicates that the sharp molecular weight selection takes place in the aggregate formation step and explains the self‐suppression. Phase equilibria studies utilizing fractionated, paucidisperse high molecular weight gelatins, emphasize the requirement for concentrated phase homogeneity and indicate that aggregates of different molecular weight may act as different components, so that χP1Q1,PkQk>0, bringing about a separation of the system into three or more coexisting phases. The formation of several coexisting phases from a homologous polyelectrolyte system and the very marked requirement for phase homogeneity suggest that the phenomenon of complex coacervation is a very good model for some of the essential steps in the pre‐biologic organization of pol

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractThe electrochemical possibilities for investigation of nucleic acids with high molecular weight are restricted to the determination of the adsorption behavior. According to our experience the alternating current polarography (Breyer‐polarography) is mainly appropriate for the characterization of changes in the secondary structure of DNA. The Breyer‐polarogram shows the alternating current of the dropping electrode in dependence on their potential which varied from 0–2 v. negative against the normal calomel electrode (NCE). By addition of native DNA to the supporting electrolyte (buffer solution) the current drops down in the range of adsorption between 0 and 1 v. At 1.16 v. against NCE the desorption takes place together with the formation of a rounded desorption peak. The investigation was carried out in phosphate buffer solution 0.1mwith 0.075mNaCl or in a phosphate buffer 0.18mwith 0.03mNaCl. In the pH range above pH 8 NaOH was added to realize the higher pH values. A calf thymus DNA sample having a mean molecular weight of about 18 million was used. The concentration of DNA was 5 × 10−3−1 × 10−1wt.‐%. The polarographic measurements were performed with an a.c./d.c.‐polarograph “GWP 564” from Akademiewerkstätten für Forschungsbedarf der Deutschen Akademie der Wissenschaften zu Berlin (DAW). The denaturation of the double helix causes a sharp desorption peak at negative potentials of the alternating current polarogram. This new criterion for the helix‐coil transition is due to formation of unpaired bases. These nearly free bases undergo a specific adsorption and the desorption takes place within a narrow potential range. Nevertheless, at present time an electron transfer to particular bases cannot be excluded at special conditions. The increase of the sharp peak permits to estimate: (a) the melting curve of the double helix in agreement with spectroscopic measurements; (b) the photolysis of the double helix; (c) the strand separation in acid and alkaline solution. In the alkaline range the sharp peak increases and reaches its maximum at pH>12. In the acid range, however, no sharp peak is observed and the rounded desorption peak decreases. Therefore, the best way of following the conformation changes is to measure the current difference between the curves of the solutions with and without DNA at electrocapillary‐zero‐potential. On the classical d.c.‐polarogram one can measure small current steps only, which may be caused mainly by capacity changes. Moreover, the scission of the molecule by ultrasonic action can be followed. In this case the rounded peak of DNA increases but the sharp peak does not appear. Similar alternating current polarograms are obtained with poly‐A in the native state, because helical and unordered regions coexist in the same molecule. The very rapid indication of these structure changes allows one to carry out kinetic measurements at a

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractThe degree of helicity θ of a series of homologous polypeptides as a function of solvent composition was investigated. The polypeptides studied were: poly‐N5‐(3‐hydroxypropyl)‐L‐glutamine (PHPG) as well as the corresponding 2‐hydroxyethyl and 4‐hydoxybutyl derivatives (PHKG and PHBG, respectively). PHPG, which is nonhelical in formic acid, attains helicity on addition of relatively small amounts of formates, formamide, and urea to its solution in formic acid. This demonstrates that the high acidity of pure formic acid is largely responsible for its helix‐breaking power‐probably through protonation of the peptide bonds. In formic acid‐water mixtures all three polymers show a maximum in degree of helicity at a mole fraction of about 0.3 formic acid. This is interpreted as being due to interaction between the two helix‐breaking solvents, which results in the formation of an inactive molecular species. It is shown that solvent‐induced transitions with helicity maxima are predicted by the Bixon‐Lifson treatment w

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractThe electronic absorption and circular dichroism spectra of the DNA‐acridine orange complex have been measured over a range of ionic strength, pH, and DNA phosphate to dye (P/D) ratios. Three circular dichroism bands associated with the long wavelength absorption band of acridine orange are induced on complex formation with DNA. Two of the dichroism bands, due mainly to dimeric dye molecules, are favored by low ionic strength, low pH (3.2), and a low P/D ratio (∼3), while the third, deriving primarily from monomeric dye, is optimum at high ionic strength, neutral pH, and a larger P/D ratio (9). The data suggest that monomeric acridine orange binds to DNA in the form of a left‐handed helical array with four dye molecules per turn, while the bound dimer has a skewed sandwich conformation which is itself dissymmetric. The stereochemical relations between the bound monomer dye and the DNA are consistent with a modified intercalation model for the DNA‐acridine

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractLight scattering of multichain poly‐α‐amino acids was studied in dimethylformamide (DMF). The polymers consisted of a backbone of poly‐L‐lysine of degree of polymerizationnwith side chains of benzylL‐glutamate and benzylL‐aspartate of degree of polymerization,m, on each ε‐amino group. The backbone lengthnis known andmis obtained by amino acid analysis. The results on a series of such materials confirm this structure and show that the molecules are dissolved in highly compacted conformations. It was found that DMF is a poor solvent for these polymers. In the case of the higher molecular weight polymers, the solutions initially were not molecularly disperse. The aggregates were resistant to dilution in the experimental range. Mild heat treatment, however, disaggregated the solutions irreversibly, and the light‐scattering data indicated that a structural rearrangement of the molec

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractThe intrinsic viscosity, sedimentation and diffusion of a series of branched, multichain poly‐α‐amino acids having a poly(L‐lysine) backbone and poly(γ‐benzylL‐glutamate) and poly (β‐benzylL‐aspartate) side chains was studied at room temperature in dimethylformamide. The molecules were found to be extremely compact structures in which the molecular backbone is either lying along the major axis in a slightly twisted configuration (the longer the side chain the smaller the twist) or is coiled up in the form of a disk with backbone and side chains coplanar. Heat treatment (to 70°C.) introduces only small changes in the hydrodynamic parameters showing that the heat‐labile aggregates detected by light scattering are reversibly broken up during the hydrodynamic measurements. The above structural information concerns the initial metastable conformation of the molecules which is irreversibly destroye

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY