摘要:

AbstractThe osmotic, sedimentation, and diffusion coefficients of sonicated sodium DNA in aqueous solutions which were rendered rigorously free of salts have been obtained in order to study the polyelectrolyte effect on these parameters. Both native and heat denatured DNA's were studied. All three parameters were found to be independent of concentration between 2 and 10 mmole/1. The osmotic coefficient gives the fraction of counterions not immobilized by the polyelectrolyte potential, under conditions of equilibrium. The value (ca. 0.18) obtained for this fraction agrees very well with that predicted by a theory of rodlike polyelectrolytes. A simplified model that permits the computation of fractions of mobile ions from sedimentation and diffusion coefficients, when applied to the experimental data, showed that under these conditions of flow between 0.5 to 0.9 of counterions are not immobilized. The experimental data also showed that for native DNA the translation frictional coefficient seems to have different values in sedimentation and diffusion, which agrees with a finding reported for another saltfree polyelectrolyte. For denatured DNA, however, the values were found to be equal: no satisfactory explanation could be found for this difference of behavior.

ISSN:0006-3525    

DOI:10.1002/bip.1969.360080102

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

年代:1969

数据来源: WILEY

摘要:

AbstractAn increase in temperature causes an increase in the amplitudes of intramolecular and intermolecular motions and mainfests itself as an increase in the effective radii of the various atoms, especially hydrogen atoms. If one uses a Lennard‐Jones 6‐12 potential function to account for nonbonded interactions, this increase in the radius of the hydrogen atom is equivalent to a modification of the coefficient of the repulsive part of the Lennard‐Jones potential. Accordingly, this effect of increasing temperature on the helix sense of several polyamino acids is computed by allowing the effective radius of the hydrogen atom to increase. It is found that the preferred sense of several polyamino acid helices changes from right‐ to left‐handed as the temperature is increased. This accounts for recent experimental observations of changes in helix sense with te

ISSN:0006-3525    

DOI:10.1002/bip.1969.360080103

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe laser‐excited Raman spectrum of helical polyglycine II has been obtained. Oligomers of polyglycine are in the planar zigzag conformation and their Raman spectra are indicative of the spectrum of polyglycine I. The Raman spectra of polyglycines have bands complementary to the infrared which are sensitive to the conformation of the chain. The spectra of the oligomers have bands sensitive to the length of the polyglycine. The Raman spectra of di‐ and triglycine in aqueous solution suggest the conformation is neither planar nor heli

ISSN:0006-3525    

DOI:10.1002/bip.1969.360080104

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe intrinsic viscosity of sonicated calf thymus DNA (molecular weight 4–5 × 105) increases and the sedimentation constant decreases, with increasing binding of proflavine at 0. 2 ionic strength and at 25°C. The measurements correspond to a linear increase in length of the almost rodlike DNA molecules with the amount of proflavine bound; independent calculations from viscosity and sedimentation measurements yield almost identical results. Over the range ofr(moles of proflavine bound per moles of nucleotides) equal to zero tor= 0.13, the length increases by about 20%. This extension is compatible with the intercalation hypothesis proposed by Lerman. Density increments at various values ofr, at constant chemical potential of diffusible solutes, were determined. It was also found that, in addition to the known isosbestic point of DNA‐proflavine complexes at 455.5 mμ, an additional isosbestic point exists at 225.5 mμ; this proved extremely useful for the evaluation of binding

ISSN:0006-3525    

DOI:10.1002/bip.1969.360080105

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

年代:1969

数据来源: WILEY

摘要:

AbstractPotentiometric titrations and some complementary optical rotation data are presented for solutions of poly(L‐ glutamic acid) (PGA) in several H2O–ethanol mixtures. The data allow the determination of the intrinsic pK(pK0), slope of the apparent. pK(pKapp), versus degree of ionization curves and of the enthalpy of ionization as a function of ethanol concentration. The variation of the degree of ionization at which the helix–coil transformation occurs with ethanol and temperature is also determined. Finally free energy, enthalpy, and intropy changes associated with the helix–coil transformation for the uncharged conformers are determined from the titration curves. The effect of the ethanol is to increase the stability of the helical conformation of PGA for both the charged and the uncharged forms of the polymer. The stabilization of the uncharged helix is essentially an entropic

ISSN:0006-3525    

DOI:10.1002/bip.1969.360080106

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

年代:1969

数据来源: WILEY

摘要:

AbstractSome experimental data are given on the infrared spectra between 3300 and 3500 cm−1of dilute solutions in carbon tetrachloride of three types of model compounds: CH3−CONH‐CH(R1)‐CONH(R2), (I); CH3‐CON(CH3)‐CH(R1)‐CONH(R2), (II) and CH3‐CONH‐CH(R1)‐CON(R2)2, (III). In studying the N‐H stretching bands, it was found that there are two types of intramolecular hydrogen bonds in these molecules; these result in two different cyclized conformations, C5and C7, which contain respectively, five and seven atoms in the ring. By using model substances I, II, and III, in which the nitrogen atoms are unequally substituted, it is possible to identify the N‐H stretching bands which are to be ascribed to the N‐H oscillators included in the two different chelated conformations. It is found also that the stretching frequency of a free N‐H oscillator depends upon the substituent on the nitrogen atom. Thus, it is possible to observe, with some of the model compounds I, four different absorption bands located at 3340, 3420, 3440, and 3460 cm−1. The first two are ascribed to the N‐H oscillators included in the Hbonds which lock the C7and C5conformations; the last two correspond to free N‐H which differ with t

ISSN:0006-3525    

DOI:10.1002/bip.1969.360080107

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

年代:1969

数据来源: WILEY

摘要:

AbstractInfrared spectra of polypeptides were measured in the region of 1800–400 cm−1. For the α‐helical form, disordered form, and antiparallel‐chain β‐form, amide V band‐ arising from N‐H out‐of‐plane bending models were observed at 610–620, around 650, and 700–705 cm−1, respectively, and amide V′ bands arising from N‐D out‐of‐plane bending modes were observed at 455–465, around 510, and a 515–530 cm−1, respectively. These correlations are useful for conformation diagnoses, particularly for copolyamino‐acids or proteins which are not oriented. The nature of low‐frequency amide bands are discussed with reference to potential energy distributions c

ISSN:0006-3525    

DOI:10.1002/bip.1969.360080108

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe mechanism of degradation of calf thymus DNA by H2O2in dark and light, and in the presence of either Cu++, Fe++, or Fe+++ions has been investigated by following the decrease of molecular weight M̄wby light scattering. Both in the dark and in light, the rate of degradation decreases in the following order: Cu++>Fe++>Fe+++. In order to exploit quantitatively the variation of M̄wwith time, we calculated the probabilityp(t) of rupture in a double stranded polymer as a function of the occurence at random of both breaks of the “first kind” (single hits) and of the “second kind” (double hits), when there are caused by any degrading agent. The value ofp(t) can then be related to M̄w(t) for the present case of a randomly polydisperse sample of DNA molecules. In the dark, and in the presence of Cu++ions, a degradation of the first kind (which takes place through the simultaneous or successive splitting of both strands of DNA at the same level) is the only one so far observed. The number of degradation sites of the first kind is equivalent to the number of bound Cu++ions in inner sites of DNA. A model is set up to explain the successive breaks of the two strands of the DNA molecule through the formation of a complex (DNA site–Cu++‐H2O2) which exhibits peroxidative properties. The comparison of the degradation induced under these conditions in a native and a sonicated DNA, shows that the specific sites of attack of ultrasonic waves are not specific sites of H2O2action in the presence of Cu++ions. In the dark and in the presence of Fe++or Fe+++ions, breaks of the first kind and second kind are superimposed, but the last are predominant. This is ascribed to the low binding of iron ions in inner sites of DNA under these conditions. A large increase in degradation rate of the second kind occurred in the presence of light (with or without added metallic ions and) is ascribed to the action of the free radicals HO·(and HO2·) which arise from the photolysis of H2O2. These results are discussed in relation to those obtained by the action of ionizing radiations on aqueous

ISSN:0006-3525    

DOI:10.1002/bip.1969.360080109

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe thermal stabilization and the configurational changes of DNA were studied during the binding process of silver ion. Melting curves of silver–DNA complexes were analyzed according to the method of Felsenfeld. An increase ofTmoccurred during the formation of the first complex with a preferential stabilization of G–C pairs. In the case of DNA fromH.influenzae, the transforming power was maintained after heating in presence of silver at a temperature where AT pairs were dissociated but G‐C pairs were not. Shape modifications of the molecule were followed by light scattering, both with native and ultrasonic degraded DNA. In the case of native DNA, the binding of positive ions modified the electrostatic potential and increased the flexibility of the molecule. In the case of rod shaped fragments of DNA, the progressive formation of a kind of polyampholyte was accompanied by aggregation phenomena. The formation of the second complex, with proton release, induced changes of secondary structure and possibly a tilt of the plane of the

ISSN:0006-3525    

DOI:10.1002/bip.1969.360080110

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe binding of cupric ion (Cu++) to DNA was followed by spectrophotometry, melting profiles, and hydrodynamic techniques, in 0. 1MNaClO4and at pH 5. 6. A small amount of Cu++is bound specifically to bases (about 1 Cu++per 20 nucleotides), in agreement with polarographic and EPR data. A preferential stabilization of G–C pairs and only a slight increase of the flexibility of the molecule were observed. In 5 × 10−3MNaClO4, a higher number of nonhomogeneous binding sites is found by spectrophotometry. It is concluded that at least two types of sites are available for Cu++. The first one, where Cu++is chelating N7of purines to phosphate, is observed only at low ionic strength and destabilizes the double helix. The second exists mainly at 0, 1Mor higher ionic strength. All the sites are identical and could be attributed to two successive guanine residues in the same strand. Similar behavior was found for other divalent cations, e. g., Fe++, Mn++, and

ISSN:0006-3525    

DOI:10.1002/bip.1969.360080111

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

年代:1969

数据来源: WILEY