摘要:

AbstractDielectric properties of human and horse hemoglobin were studied at frequencies ranging from 20 kc./sec. to 7 Mc./sec. The relative errors in the measurements were usually less than 10−3even for mildly conducting solutions (10−3M KCl). The experimental setup allowed us variation and measurement of the degree of oxygenation of the protein and to determine its dielectric parameters. Our main conclusion is that it was not possible to find any variation of the dielectric increment for hemoglobin oxygenation levels of 25, 50, 75, and 100%, approximately. This result is at variance with some previous reports. We cannot give the reason for this discrepancy but discuss some possible explanations. The specific dielectric increment, Δεs/c, of human hemoglobin was shown to be significantly smaller than that of horse hemoglobin (0.28 against 0.32). This physical property is lowered with increasing ionic strengthI: Δεs/c = 0.28 and 0.20 forI= 10−4and 10−3, respectively (hum

ISSN:0006-3525    

DOI:10.1002/bip.1967.360051002

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

年代:1967

数据来源: WILEY

摘要:

AbstractComplex shear viscosity η* = η′ –iη″ of poly (L‐glutarmic acid) solution was measured by the torsional crystal method at 50 kc./sec. as a function of pH. A sharp peak was found at the midpoint of the helix‐coil transition region in both η′ and η″. The relaxation time is calculated from η′ and η″ assuming a single relaxation process and the peak value at the midpoint of transition is estimated at 10−6sec. Such behavior agrees well with the prediction from the theory of Schwarz. The attenuation of longitudinal sound waves at,3 Me./sec. was measured as a function of pH for solutions of poly(glutamic acid), glutamic acid, and gelatin. A small attenuation peak was observed for the three solutions, the peak height being almost, the same for them. The peak is interpreted in terms of the dissociati

ISSN:0006-3525    

DOI:10.1002/bip.1967.360051003

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe dielectric relaxation of DNA solutions has been investigated with and without extraneous ions covering a wide frequency range. The effect of monovalent ions such as Na, K, and Li as well as divalent ions such as Mg, Ca, and Hg have been included in the study. These ions are found to have a profound effect on the dielectric increment and the relaxation time without affecting the molecular dimension drastically. This dielectric effect is interpreted as indicating the importance of counterion fluctuation on the low frequency dielectric constant of DNA in solution. The effect of an organic ion, tetra‐methylammoniun bromide, has also been studied. This ion has no noticeable effect. A simple theory is derived on the basis of a microscopic model to account for the effect of external ions on the dielectric behavior of solutions of DN

ISSN:0006-3525    

DOI:10.1002/bip.1967.360051004

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

年代:1967

数据来源: WILEY

摘要:

AbstractWe report the circular dichroism (CD) spectrum of poly‐Lacetoxyproline in trifluoroethanol, a solvent in which the form I to form II conformational isomerization occurs slowly enough to permit observation of the spectral changes. A comparison is made to poly‐Lproline. As judged by the similarity of the CD spectra, the conformations of the corresponding forms of the two polymers must be nearly the same. Transition assignments are proposed; these are shown to agree with the theoretical calculations of Pysh. There is a serious unexplained discrepancy between our solution data and those of Fasman for poly‐Lacetoxypr

ISSN:0006-3525    

DOI:10.1002/bip.1967.360051005

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

年代:1967

数据来源: WILEY

摘要:

AbstractFar‐infrared spectra ofN‐methylacetamide and other monosubstituted amides were measured in the liquid state in the region from 250 to 60 cm.−1. Bands characteristic of the molecules with a peptide bond were found and assigned to the hydrogen‐bond vibration and the CN torsional vibration. Far‐infrared and Raman spectra of crystallineN‐methylacetamide were measured. The normal coordinate treatment for the low‐temperature modification of cystallineN‐methylacetamide was made. A reasonable set of force constants can explain all the spectra and their change due to the modifi

ISSN:0006-3525    

DOI:10.1002/bip.1967.360051006

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe Lifson‐Roig and Zimm‐Bragg theories of the helix–coil transition in polypeptides are generalized to include both right‐ and left‐handed α‐helical states. The partition functions for these more general theories are formulated in terms of the parametersu,vR,VL,WR, andwLfor the generalized Lifson‐Roig theory and σR, σL,sR, andsLfor the generalized Zimm‐Bragg theory. Matrix equations are derived for calculating such average molecular properties as the fraction of the amino acid residues hydrogen bonded into right‐ and left‐handed α‐helices, the average number of right‐ and left‐handed helical sequences per molecule, the number‐average length (in residues) of the right‐ and left‐handed helical sequences, and the degree of solvent binding to the peptide NH and CO groups. These equations are shown to be conveniently adaptable to machine methods of calculation, thus avoiding the difficulty of solving an eigenvalue problem where the secular equation is of a high order. A discussion is given of the various energetic and entropic effects which determine the screw sense and stability of helices and of the extent to which it is valid to interpret experimental data by adjustment of the parameters of these statistical mechanical theories which include in their formulation only near‐n

ISSN:0006-3525    

DOI:10.1002/bip.1967.360051007

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe half molecules of 186 DNA have been isolated by the Hg(II)–Cs2SO4density gradient centrifugal ion technique. The buoyant densities of the two halves in CsCI at 25°C. are 1.713 and 1.709 g./cm.3, corresponding to GC contents of 54% and 50%, respectively. Similarly, 5‐bromouracil labeled λ DNA halves were separated. The isolation of the four DNA halves made it possible to test for homology in base sequences between the cohesive ends of λ and those of 186. There was no indication of any significant homology in base sequences between the cohesive ends of the two DNA's, as indicated by the absence of a band with intermediate buoyant density in CsCI when either half of 186 DNA was annealed with either half of 5‐bromouracil labeled λ DNA and then centrifuged. The lack of cohesion between the two DNA's made it possible to demonstrate unequivocally the formation of interlocked rings (catenanes) between the two DNA's. The existence of a dimeric catenane is evidenced by the formation of a species of intermediate buoyant density when 5‐bromouracil labeled λ DNA is cyclized in the presence of cyclic 186 DNA of a relatively high concentration. The molecular weight of one DNA relative to the other can be calculated from the position of the dimeric catenane in a density gradient by using the method of Baldwin. The result was in complete agreement with our previous measurements from the sedimentation coefficients and by electron microscopy. The probability of dimeric catenane formation when one DNA is cyclized in the presence of another DNA is discussed. The experimental results agree with the theoretical

ISSN:0006-3525    

DOI:10.1002/bip.1967.360051008

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe thermal helix–coil transition of DNA can be studied by means of the spin‐echo technique. The longitudinal spin–lattice relaxation timeT1 and the transvense spin–spin relaxation timeT2 of the DNA sample show a similar phase transition as observed spec‐trophotometrically with increasing and decreasing temperatures. Four slopes on theT1 andT2 temperature relationship curves were found and interpreted as functions of nonrelational hydration of the DNA molecule. TheT1 andT2 values differ depending on the native or denatured state of the DNA molecule. The importance of the dynamic equilibrium between water molecules in the hydration lattice and steps in the denaturation of the DNA molecule are discussed. This phenomenon may be directly related to the nonrotational

ISSN:0006-3525    

DOI:10.1002/bip.1967.360051009

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

年代:1967

数据来源: WILEY

摘要:

AbstractAn approximate analytical expression for the electrostatic free energy of a polynucleo‐tide in any of its possible ordered or random conformations is derived by integration of the screened‐Coulomb potential energy function over all charge pairs in the structure. The electrostatic free energy of any form is found to be a linear function of the logarithm of the monovalent counterion concentration, in the range of low salt concentrations. Hence the electrostatic free energy difference between ordered and disordered forms in a polynucleotide structural transition is a linear function of the logarithm of the monovalent counterion concentration. A free energy balance applied to a two‐state model for the transition then yields a linear dependence of the transition temperatureTmupon the logarithm of the counterion concentration. Calculation of the quantitydTm/dlogM, whereMis the monovalent counterion concentration, shows it to be a characteristic constant for a given transition, with a magnitude and sign proportional to the charge density difference between the ordered and disordered forms. Use of any one of several alternate, simple assumptions yields predicteddTm/dlogMvalues in good agreement with experimental data for various polynucleotide transi

ISSN:0006-3525    

DOI:10.1002/bip.1967.360051010

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe theory developed in the previous paper to discuss changes in electrostatic free energies in polynucleotide order–disorder transitions is extended to cases where one or more of the participating species is titrated to some degree α. It is shown that, for any class of transition, the melting temperatureTmat constant pH is a linear function of the logarithm of the monovalent counterion concentrationM, that at high salt the logarithm of the depression of the melting temperature by pH titration is proportional to the pH change, and that the stability of the ordered form as measured by its melting temperature at neutral pH, is a monotonic function of the quantity pHm– pK, where pHmand pKare the pH of melting and the monomer base pK, both measured under similar conditions of temperature and ionic strength. For the transition from double helix to coil, the dependences ofTmanddTm/d logMon pH are determined experimentally and compared with the qualitative predictions of the theory. It is found thatdTm/dlogM, a measure of – ΔF̄el(the negative of the electrostatic free energy change in the transition), decreases with increasing pH. In acid solution, where the coil is more extensively prolonated than the helix, the change in electrostatic free energy in the transition is larger than at neutral pH. Conversely, in alkali the electrostatic five energy change is smaller than at neutral pH. Hence (dTm/dlogM)acid>(dTm/dlogMneutral)>(dTm/dlogM)alkali. At Suffeciently high pH,dTm/dlogMis observed to become negative, indicating that the electrostatic free energy change is positive in the transition of this region. Date from the literature on the ionic strength dependence of the melting temperature for the acid helices of poly rA, poly rC, and poly dC are also considered from the standpoint of th

ISSN:0006-3525    

DOI:10.1002/bip.1967.360051011

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

年代:1967

数据来源: WILEY