摘要:

AbstractProcedures are developed which make a first neighbor frequency analysis possible from a CD spectrum of homopyrimidine: homopurine DNA's. The contribution to the CD spectrum from the various first neighbor frequencies present in homopyrimidine: homopurine‐type DNA's has been determined, and hence the CD spectrum for any DNA of this type with known first neighbor frequencies can easily be calculated. An identical analysis is presented for the determination of extinction coefficients. It is further shown that unlike the more usual heteropurine–pyrimidine DNA's a random sequence does not lead to a simplified formalism. Finally, it is concluded that the homopyrimidine: homopurine DNA's have a structure that is different from that of the more usual heterobase DNA's.A procedure capable of determining first neighbor frequencies from a CD spectrum for heterobase and/or homopurine: homopyrimidine DNA's is described. This procedure is used to determine that there is only minimal interference between these two types of DNA in the first neighbor analy

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130202

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe small‐angle equatorial X‐ray scattering of alpha keratin (African porcupine quill) was studied using a direct type of analysis, which allows the separation of the intermicro‐fibrillar interference effects from those of the intramicrofibrillar scattering without the use of prior assumptions. X‐ray data were obtained from 470–21 Å; their analysis by the above method resulted in az‐axis projection of the microfibrillar electron density, which extends over a diameter of 80 Å and has a core region surrounded by a peak located at a radius of 28 Å. The macromolecular organization of the 80‐Å‐diameter microfibrils was found to be an arc‐like layer type of aggregation and not a pseudohexagonal packing. When the specimen was subjected to silver staining the aggregation of the microfibrils did not change except for a slight contraction. Thez‐axis projection of the stained microfibril, however, was significantly different. The silver appears to build up slightly around the outer periphery of the microfibril, stains the peripheral region very little, deposits on the inside of the peripheral region, and

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130203

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

年代:1974

数据来源: WILEY

摘要:

AbstractTheoretical calculations of the kinetics of a polymerization reaction have been carried out for a scheme in which there is a nucleation step that is slow relative to subsequent propagation steps.A transient maximum (overshoot) in molecular weight can be expected in such reversibly self‐associating systems when polymerization is initiated suddenly. The extent of overshoot decreases with increasing initial concentration of true equilibrium is strongly dependent on the rate of nucleus formation and the rate of depolymerization when the absolute values of both are small relative to the rate of propagatio

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130204

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

年代:1974

数据来源: WILEY

摘要:

AbstractSemiempirical molecular orbital studies were performed on 5′‐guanosine monophosphate in its various states of base and phosphate ionization (employing the extended Hückel method) and on guanosine protonated on N‐3 and on N‐7 (employing CNDO/2). Semiempirical potential energy calculations (Lennard–Jones and Coulombic) failed to pinpoint the reasons for the recent experimental suggestion that guanine protonation increases thesynpopulation in 2′‐ and 3′‐guanosine monophosphates. Changes in electron densities upon base protonation are much in evidence and are a very sensitive function of the site of base protonation assumed. It is suggested that the CNDO/2‐type calculations when combined with13C and15N pH‐dependent chemical shifts can lead to assignment of the site of proton

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130205

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

年代:1974

数据来源: WILEY

摘要:

AbstractRaman spectra in the region 1000–150 cm−1were measured for copoly(D,L‐alanines) with theD‐residue contents, 3, 7, 10, and 20%, and compared with the spectrum of the α‐helical poly‐L‐alanine. The 532‐ and 378‐cm−1peaks were assigned to theL‐residues with a right‐handed α‐helix‐like local conformation or to theD‐residues with a left‐handed α‐helix‐like local conformation. From the intensity of the latter peak the contents of these local conformations were estimated as a function of theD‐residue contents for the copolymers. The 264‐cm−1peak, which has been assigned to the breathing vibration of the α‐helical poly‐L‐alanine, shows a marked decrease in its intensity upon the introduction of theDresidues. This result suggests that the overall deformation vibration of the α‐helix arises from rather long sequences of theL‐ andD‐alanine residues with the α‐helical conformation and that the intensity of this vibratio

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130206

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

年代:1974

数据来源: WILEY

摘要:

AbstractConformational analysis of DNA–basic polypeptide complexes, based on stereo‐chemical criteria and energy calculations and experimental results, is reported. Three types of polypeptide conformations were selected: the distorted β conformation similar to that proposed by Feughelmann et al.; a structure characterized by a repetition of a right‐handed and left‐handed α helix‐type conformation; and an intermediate structure. A model of the complex between DNA and basic polypeptides was proposed, where the polypeptide chain fits the narrow groove of the B form of DNA. Van der Waals, hydrogen bond, electrostatic, and hydrophobic forces cooperate to stabilize the association complex. This structure also seems to be suitable to represent the molecular model of nucleoprotamines. In the case of nucleohistones, both grooves of DNA are involved in the interaction with the proteins. These have the nonbasic‐rich portion in the α‐helical conformation, whereas the part where a greater proportion of basic amino acids occurs presents a structure similar to nucleoprotamines and complexes between DNA and basic homopolypeptides. The distribution of basic residues of the F2A1(IV) histone on DNA is markedly disproportionate for the two opposite cylindrical sectors of the double helix. This suggests a new mechanism of supercoiling in

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130207

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

年代:1974

数据来源: WILEY

摘要:

AbstractUsing the thermodynamic analysis and methodology of Hill (Biopolymers,12, 257 (1973)) for the treatment of optical thermal transition data the effects of various neutral salt additives on the stability and thermodynamics of the poly U–deoxyadenosine interactions that lead to the formation of triple‐stranded helical polymer–monomer complexes have been studied. In order of increasing molar effectiveness as polyU–deoxyadenosine complex stability perturbants (pH 7 and in the presence of 1MNaCl), the various ions may be ranked: SO4−2

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130208

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe thermal effect of magnesium ions on the helix–coil transition of DNA was studied calorimetrically by a modified differential scanning calorimeter (DSC). It was found that the transition temperature of DNA depends on both the DNA and magnesium ion concentrations. The dependence of the helix–coil transition of DNA on the mole ratio of magnesium ions to DNA(P) can be classified into two groups. When this mole ratio is less than 1, magnesium ions tend to stabilize the double‐helix DNA, so that the transition temperature increases linearly and the heat of transition increases significantly with increasing mole ratio. When the mole ratio is more than 1, magnesium ions tend to destabilize the double‐helix DNA, so that DNA precipitates when the temperature is raised above the transition temperature. In this case, both the transition temperature and the heat of transition decrease with increasing mol

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130209

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe CD spectra of films of the lithium salt ofE. coliand calf thymus DNA, and alternating d‐AT : AT were measured as a function of relative humidity. Films of the ammonium acetate salt of DNA were also measured. The ammonium films yield the previously reported A‐form CD spectra. A possible explanation for the small magnitude of the 260‐nm band of the A‐form film spectra compared to double‐stranded RNA spectra is that the film DNA is in a different conformation than RNA within the A family of conformations.At relative humidities of 92% or lower, a negative nonconservative CD spectrum with negative minima near 270 and 210 nm is observed with the lithium films. The magnitude of the minima varies from film to film. In films of DNA the magnitude ranges from a delta epsilon of −5 to −35; d‐AT : AT films show magnitudes to −300. CD spectra of this type are designated Ψ spectra. Similar spectra have been reported from reconstituted complexes of DNA and polylysine or f‐1 histone. If the origins of the film and protein–DNA complex spectra are similar, the complex spectra are not the result of specific secondary structural changes induced in the DNA by the protein fraction. Theoretical analysis suggests that Ψ spectra are not the result of changes in the secondary or tertiary structure of DNA. Instead, the previously proposed explanation based on liquid crystals is favored. The DNA could form asymmetric structures with long‐range periodicity. It is likely that the observed CD spectra of f‐1 complexes are artifacts of DNA aggregation. The possibility that some other previously published spectra of protein–DNA complexes also r

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130210

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe 218‐nm peak, characteristic of the circular dichroism of randomly coiled poly‐α‐amino acids can be demonstrated in solutions of penta‐L‐lysine, α‐glycyl‐L‐lysine, as well as poly‐L‐lysine. The thermal stability of the particular state that gives rise to this 218‐nm band in the CD is similar for all three peptides. These results eliminate the possibility that poly‐L‐lysine forms a structure with long‐range order in acidic aqueous solution since the stability of such a structure would be expected to be greater for a higher molecular weight polymer than for a pentamer. The intrinsic viscosity of poly‐L‐lysine of molecular weight 180,000 varies only slightly between 25 and 60°C. The proton magnetic resonance spectra of poly‐L‐lysine and penta‐L‐lysine are indistinguishable on the basis of the chemical shift of all resonances, their line widths, and the exchange rates of the NH protons. This demonstrates that poly‐L‐lysine does not possess a cooperatively formed ordered structure in acidic solutions.A weak band at 238 nm is observed in the circular dichroism of poly‐L‐lysine and other peptides. It is suggested that the effects of change in temperature, salt concentration, or polymer on both the magnitude and position of the 238‐nm band may be explained if it is as

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130211

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

年代:1974

数据来源: WILEY