摘要:

AbstractDifferential scanning calorimetry studies of the effect of NaCl on protein‐based polymer self‐assembly has been carried out on six elastin‐based synthetic sequential polypeptides‐ i.e., the polypentapeptide (L‐Val1‐L‐Pro2‐Gly3‐L‐Val4‐Gly5)nand its more hydrophobic analogues (L‐Leu1‐L‐Pro2‐Gly3‐L‐Val4‐Gly5)nand (L‐Val1‐L‐Pro2‐L‐Ala3‐L‐Val4‐Gly5)n; the polytetrapeptide (L‐Val1‐L‐Pro2‐Gly3‐Gly4)nand its more hydrophobic analogue (L‐IIe1‐L‐Pro2‐Gly3‐Gly4)n; and the polynonapeptide (a pentatetra hybrid), (L‐Val1‐L‐Pro2‐Gly3‐L‐Val4‐Gly5‐L‐Val6‐L‐Pro7‐Gly8‐Gly9)n.Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order of the polypentapeptide, as the temperature is raised from below to above that of the transition, has been repeatedly observed using different physical characterizations.In the present experiments, it is observed that the transition temperatures of the polypeptides studied are linearly dependent on NaCl concentration. The molar effectiveness of NaCl in shifting the transition temperature ΔTm/[N], is about 14°C/[N], with the dependence on peptide hydrophobicity being fa

ISSN:0006-3525    

DOI:10.1002/bip.360310502

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

年代:1991

数据来源: WILEY

摘要:

AbstractHeat capacities of polyglycine, poly(L‐alanine), and poly(L‐valine) were analyzed using approximate group vibrations and fitting of the skeletal vibrations to a two‐parameter (Θ1, Θ3) Tarasov function. New experimental data were measured by differential scanning calorimetry in the temperature range of 230–390 K. Good agreement between our experimental data and the calculated data was observed for all three poly(amino acids). Previous investigations showed agreement between calculation and reported experimental data for only limited low temperature ranges. At higher temperatures, discrepancies of up to 55% existed between experiment and calculation. The cause of this discrepancy must be assumed to be experimental error. Recommended experimental data are revised on the basis of this investigation. Computed heat capacities are available for the three biopolymers in the solid state from 0

ISSN:0006-3525    

DOI:10.1002/bip.360310503

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe reversible thermally induced unfolding of various forms of tropomyosin, a two‐chain α‐helical coiled coil, has been studied by high‐sensitivity differential scanning calorimetry (DSC). Included in the study are the reduced and oxidized (disulfide cross‐linked) forms of αα‐ and ββ tropomyosin, and the forms of αα‐tropomyosin in which all sulfhydryl groups have been blocked by carboxymethylation or carboxyamidomethylation. Oxidation or blocking of the sulfhydryl groups of tropomyosin strongly affect the thermotropic behavior of the protein in unpredictable ways. The empirical results presented here are in qualitative agreement with those from an earlier DSC study of the oxidized and carboxymethylated forms of αα‐tropomyosin [ S. A. Potekhin and P. L. Privalov (1982)Journal of Molecular Biology, Vol. 159, pp. 519‐535], but we find that a different decomposition into subtransitions is possible. Comparison of the αα and ββ species indicates, in agreement with extant CD studies, that the noncross‐linked ββ species is somewhat less stable than its αα counterpart, but that cross‐linking enhances the stability of the ββdoubly cross‐linked species by a greater amount and does not lead to the small low‐temperature transition (“pretransition

ISSN:0006-3525    

DOI:10.1002/bip.360310504

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

年代:1991

数据来源: WILEY

摘要:

AbstractCD spectra of reduced and S‐3‐(trimethylated amino) propylated lysozyme (TMAP lysozyme) have been measured in various solutions containing guanidine hydrochloride or trifluoroethanol (TFE). The CD spectra indicate that there remain residual secondary structures in protein in aqueous solution. The addition of TFE further promotes the formation of secondary structures. In order to examine whether secondary structures are evenly induced over all the polypeptide chain, or locally at particular segments, the limited proteolysis of TMAP lysozyme by trypsin has been performed, and the CD spectra of all the final and intermediate products have been observed in solutions containing TFE. As a result, the fragments vary in a helix‐forming propensity. The CD spectra of peptide fragments T5, T7, T9T10, T12T13, T14T15T16, and T17T18 are not significantly affected by the addition of TFE, where T refers to the nomenclature of R. E. Canfield [(1963),Journal of Biological Chemistry, Vol. 238, pp. 2691–2697]. They are fragments of a helix‐breaking propensity. On the other hand, fragment 12 composed of T1‐T4, and fragments T6T7, T8, and T11, attain secondary structures with the addition of TFE. They are fragments of a helix‐forming propensity. Further, it is found that the fragments of a helix‐forming propensity just correspond to the helical segments in native lysozyme. We examine the interactions between neighboring fragments, which contribute to the stabilization of local structures along the po

ISSN:0006-3525    

DOI:10.1002/bip.360310505

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe ability of tracts of synthetic oligopurine · oligopyrimidines containing both adenosine and guanosine residues to approach the conformation of analogous polypurine · polypyrimidines has been examined as a function of tract length by CD spectroscopy. Tracts of up to 19 contiguous, alternating dA and dG residues yield CD spectra that are distinctly different from that of the analogous alternating polymer. Thus the structural changes reflected in the unusual CD spectrum of poly[d(AG)] · poly [d(CT)]must require even longer tract lengths. Tracts of contiguous adenosines flanked by guanosine residues were seen to approach the CD spectrum of poly[dA] · poly[dT]quite slowly as a function of tract length, requiring more than 24 contiguous adenosines to give CD spectra similar to the homopolymer. These results lead us to the conclusion that oligopurine tracts in vivo are not well modeled by synthetic polypurine · polypyrimidines with one or two base pair repeating u

ISSN:0006-3525    

DOI:10.1002/bip.360310506

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

年代:1991

数据来源: WILEY

摘要:

AbstractViscosimetric and kinetic results allow one to characterize three modes of DNA binding in the ellipticine series: (1) Ellipticine and its 9 methoxy derivative, which present maximal DNA lengthening properties and bind DNA through a single step mechanism, can be considered as pure intercalators. (2) Ellipticinium derivatives and short‐chain substituted oxazolopyridocarbazoles, which present intermediate DNA lengthening properties, bind DNA through a two‐step mechanism, one being intercalation. (3) Long‐chain substituted oxazolopyridocarbazole derivatives, which display the smallest DNA lengthening properties, bind DNA through a single‐step mechanism, probably resulting from an outside binding mode.The viscosimetric and kinetic results are compared with the thermodynamic results obtained from the temperature dependence of the binding constants. It appears that drugs binding on the outside of the DNA double helix tend to have large enthalpy and small entropy contributions, whereas pure intercalating drugs have contributions from both enthalpy and entropy, with entropy dominating by about 2 : 1. Drugs showing two binding modes exhibit a continuum between the aforementioned extremes, with no breaks in behavior.From this comparison, a correlation between thermodynamic data and DNA binding modes is proposed. Possible molecular implications of both enthalpy and entropy to DNA binding free energy are di

ISSN:0006-3525    

DOI:10.1002/bip.360310507

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

年代:1991

数据来源: WILEY

摘要:

AbstractAbsorption and CD spectra of the π‐π* transition near 200 nm are calculated for helical (Pro)10forms I and II with a variable proline ring conformation characterized by torsion angle χ2in the range −60° to 60°. The spectra for poly (Pro) I are not sufficiently sensitive to χ2to suggest a preferred ring conformation. The spectra for poly (Pro) II are more sensitive to χ2, and suggest preferred ring conformations near either or both of the χ2regions −50 ± 10

ISSN:0006-3525    

DOI:10.1002/bip.360310508

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

年代:1991

数据来源: WILEY

摘要:

AbstractOligomers of (−)‐epicatechin with 4β → 8 interflavan bonds, and as many as five monomer units, have been studied by conformational analysis and time‐resolved fluorescence. The conformational analysis yields 2x−1conformations for each oligomer withxmonomer units. There are two conformations accessible at each interflavan bond. These conformations are denoted by + and −. The dominant conformations for the trimer and higher oligomers have an interaction between the phenolic hydroxyl groups on monomersiandi+2. This interaction involves the hydroxyl group at C(5) on monomeri, and either C(13) or C(8) of monomeri+2, depending on whether the conformation of the two intervening interflavan bonds is + + or + −, respectively. Minor contributions to the ensemble for the tetramer and pentamer are made by conformations that contain the sequence of successive interflavan bonds denoted by −+ or −−. In −+ the interaction between monomer unitsiandi+ 2 involves an aliphatic hydroxyl with a phenolic hydroxyl, and there are no hydroxyl‐hydroxyl interactions between unitsiandi+ 2 in −−. The onset of a different decay law for the fluorescence whenxincreases from 3 to 4 may be associated with the appearance of the −+ and −− conformations as

ISSN:0006-3525    

DOI:10.1002/bip.360310509

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

年代:1991

数据来源: WILEY

摘要:

AbstractA theory is presented for the dynamic structure factor [S(K, t)] of weakly bending rods. This treatment is based on a discrete bead model for the Brownian dynamics in which all bead motions associated with bending are constrained to occur in a plane perpendicular to the end‐to‐end vector, thus prohibiting extension or contraction along that axis. Preset hydrodynamic interactions are incorporated in a numerically exact manner. The predicted normalized dynamic structure factorS(K,t)/S(K, 0) should be valid for short timestsuch that the rms rotation of the end‐to‐end vector around any transverse axis is much less than 1.0 radian. With geometrical parameters appropriate for the M13 virus, the intensity autocorrelation functionG(2)(K,t) = 1 + |S(K,t)/S(K, 0)|2is calculated over a range of times and scattering vectorsKfor selected values of the persistence lengthP.The calculatedG(2)(K,t) are fitted to a single exponential with unit baseline over the same range of times as the experimental photon correlation functions, and the apparent diffusion coefficientsDapp(K) are obtained from the best‐fit relaxation times. For the sake of completeness, an exact expression is derived for the apparent diffusion coefficient obtained from the initial slope of the dynamic structure factor. However, this does not reduce to the known correct result in the rigid rod limit. To obtain the correct result, the limit of infinite bending rigidity must be takenbeforethe limit of zero time. For this and other reasons, the initial slope value of Dapp(K) is not useful for weakly bending rods.Photon correlation functions are measured for the M13 virus, which is virtually identical to the often‐studied fd virus. The experimental photon correlation functions are fitted over 8 relaxation times to a single‐exponential plus baseline, and theDapp(K) are calculated from the best‐fit relaxation times. Theoretical curves ofDapp(K) vsK2for selected values ofPare compared with the experimental data, which are satisfactorily reproduced whenP= 22000 ± 2000 Å. This dynamic value is close to the static value,P= 20000 ± 2000 Å, reported for the very similar fd virus. The most recent theories of Maeda and Fujime and their dynamic light scattering studies of fd virus are compared with the present results in some detail. Their optimum value ofPis in surprisingly good agreement wit

ISSN:0006-3525    

DOI:10.1002/bip.360310510

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

年代:1991

数据来源: WILEY

摘要:

AbstractAn improved model for calculating the CD of polypeptides has been developed. Excited state wavefunctions were derived from CNDO/S (complete neglect of differential overlap, spectroscopic) calculations on N‐methylacetamide. Four discrete peptide‐localized transitions were employed: π0π*(NV1), π+π* (NV2),nπ*, andn′π*. Inclusion of the π+π*transition (λ0= 140 nm) significantly improves the accuracy of the calculated CD spectra in the 180‐250‐nm region. Spectra were computed for various helical structures, including right‐handed α‐, αII‐, ω‐, π‐, 310‐, and poly(proline)I‐helices, and the left‐handed poly(proline)II‐helix. Sensitivity to changes in the peptide backbone geometry and chain length are examined. Electronic factors such as ground‐state charge distribution, hybridization effects, and basis set deorthogonalization have been investigated. The nonconservative nature of the poly (Pro) I and II CD spectra is reproduced, and the helix band present in earlier exciton calcu

ISSN:0006-3525    

DOI:10.1002/bip.360310511

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

年代:1991

数据来源: WILEY