摘要:

AbstractThe Raman and infrared spectra of poly(L‐lysine) and poly(DL‐lysine) in solution are reported and the effects of various salts are investigated. The results demonstrate that α‐helix formation in solution is induced by specific salts and the spectral data support the hypothesis of regions of local order for poly(L‐lysine) in aqueous solutions of low ionic

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150202

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe hyperchromic and hypochromic changes in the intensity of the amide‐I and amide‐III lines of polypeptides and certain ring vibrations of the bases of polynucleotides are shown to be related to similar changes in the lower energy uv absorption bands. The selection rules strictly limit the pairs of excited electronic states that can contribute to the elements of the polarizability matrix. An energy‐dependent term in this equation weights the contribution of the pairs of electronic transitions in favor of those involving the lower energy transitions. For both polypeptides and polynucleotides, there is a large hypochromic inensity change in the first π → π* exciton band upon the coil‐to‐helix transition. Through the selection rules, certain conformationally sensitive Raman lines are shown to derive their intensity predominantly from this band and hence also display hypochromism. Again, through an application of the selection rules, certain Raman lines can be demonstrated to depend predominantly for their intensity upon then→ π* transition, and consequently have the opposite hyperchromic intensity change upon the same conformat

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150203

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe adsorption of protein films on polystyrene latex spheres was studied by optical mixing spectroscopy. With this technique, we show that both the hydrodynamic thickness of protein films and their optical density can be measured. Thus, we found that films of the glycoproteins isolated from the human erythrocyte membrane were four times as thick as films of either human serum albumin or bovine serum albumin for about the same surface coverage. This result suggests an end‐on orientation for the adsorbed glycoprotein molecules, which is consistent with the model proposed by others for the orientation of these molecules at the surface of the red blood cell itsel

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150204

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

年代:1976

数据来源: WILEY

摘要:

AbstractPrecision density measurements were performed at 25°C on Na‐DNA‐Na2SO4mixtures in the presence of either 0.005mcacodylic acid buffer (pH 6.8) or in the presence of 0.1mNaOH (pH 12.3). From measurements executed under equilibrium dialysis conditions, the so‐called “density increments” (∂ρ/∂c2)μ0for native (pH 6.8), heat‐denatured (pH 6.8), and alkali‐denatured (pH 12.6) Na‐DNA were evaluated as a function of Na2SO4concentration. (∂ρ/∂c2)μ0for native DNA was found to decrease almost linearly with ionic strengthI1/2of the supporting electrolyte. The density increment for Na‐DNA at pH 12.6, on the other hand, increases in more or less linear fashion withI1/2. (∂ρ/∂c2)μ0for heat‐denatured DNA at pH 6.8 is not affected very much by increasing salt strength. From density measurements performed on the Na‐DNA–Na2SO4mixtures at fixed concentrations of diffusible components, the partial specific volumesν2° of native (pH 6.8), heat‐denatured (pH 6.8), and alkali‐denatured (pH 12.6) Na‐DNA were determined as a function of Na2SO4concentration. Allν2° values, irrespective of the secondary structure of the DNA, increase with increasing salt concentration although the increase for heat denatured DNA (pH 6.8) is barely noticeable.ν2° of both native and heat‐denatured DNA (pH 6.8) extrapolates to a value of 0.50oml/g at vanishing salt concentration;ν2° of DNA in 0.1mNaOH, on the other hand, assumes the value 0.2oml/g.Distribution coefficients of diffusible components, expressed in terms of preferential water and salt interaction, were evaluated from the (∂ρ/∂c2)μ0data, solvent densities, and partial specific volumes of all solution components. All interaction parameters depend strongly on salt concentration and on the conformation of DNA. From data collected and from information available in the literature it is concluded that Na2SO4, for instance, displaces water of hydration from native DNA much more readily with increasing salt concentration than does NaCl. The solvation properties of the denatured forms of Na‐DNA are rather complex but appear to be in har

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150205

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe low‐temperature relaxation of native ox Ligamentum nuchae elastin and of two purified elastin samples has been investigated in the dry state by means of the Rheovibron DDV II viscoelastometer, at the fixed frequencies of 3.5, 11, 35, and 110 Hz. Besides the glass transition at about 200°C, a relatively strong secondary loss‐tangent peak, whose activation energy is about 13 kcal/mol, is found for all samples below room temperature. The peak maximum is at −71°C for the 3.5‐Hz frequency. On the basis of its location, intensity, and width, it is attributed to a main‐chain relaxation of the pure protein. When suitable reduced variables are used, the loss‐tangent‐temperature curves obtained at different frequencies can be satisfactorily superimposed to give a master curve. Comparison of the data with the prediction of a semiempirical viscoelastic model can also be consider

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150206

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

年代:1976

数据来源: WILEY

摘要:

AbstractSolvent binding to bovine serum albumin in 2‐chloroethanol‐water mixed solvents of different composition, measured previously by Inoue and Timasheff (Biopolymers(1972)11, 737–43) is applied to a hydrodynamic study of the solvated protein.From sedimentation and diffusion data, the apparent molecular weight of the solvated protein particle can be calculated, provided an average partial specific volume, computed from the composition of the particle, is introduced in Svedberg's equation. The unsolvated molecular weight of the protein can than be calculated by subtraction of the bound solvent. Further data on the hydrodynamic particle (f/fminand axial ratio of the equivalent ellipsoid) are readily calculated from these experiments, and reinforce the supposition that 2‐chloroethanol is a strong helix‐inducin

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150207

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

年代:1976

数据来源: WILEY

摘要:

AbstractTransient electric birefringence experiments have been performed on well‐characterized highly monodisperse samples of tobacco mosaic virus (TMV). Experiments and calculations are presented that show that the sensitivity and accuracy of the traditional transient electric birefringence technique can be enhanced by several orders of magnitude through the use of a low‐powered laser and crystal polarizing optics, signal averaging, and digital data processing. Measurements of the field‐free decay of the birefringence yield for the rotational diffusion coefficient,DR= 318 ± 3 sec−1. The length of the rodlike virion, calculated from the Broersma equation with this value ofDRand a rod diameter of 15 nm, is 292.5 ± 1.0 nm. Measurements of the growth of the birefringence when an electric field is applied across the sample yield μ2/kT(α∥− α⊥) = 0.47 ± 0.07, where μ is the permanent dipole moment (assumed parallel to the symmetry axis of the virus) and α∥− α⊥is the electrical polarizability anistropy of the virus. Using the value of α∥− α⊥measured by O'Konski et al.,

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150208

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

年代:1976

数据来源: WILEY

摘要:

AbstractRacemization in the synthesis of tripeptide intermediates and their polymers was investigated, usingL‐amino acid oxidase. Stepwise investigation of peptide intermediates showed no racemization during peptide coupling steps or deprotection of benzyl esters by hydrogenolysis. Saponification of one of the methyl esters produced some racemization. Preparation of active esters fromN‐protected tripeptide acids containing optically active C‐terminal amino acid, with one exception, produced racemization. The fractionated polymers were found to contain less racemized amino acids than the crude products or starting monomeric tripeptides, indicating that the racemized sequences gave rise to lower molecular‐weight oligomers. The sequences investigated were ‐Pro‐Pro‐Ala‐, ‐Ala‐Pro‐Pro‐, ‐Val‐Pro‐Pro‐, ‐Pro‐Pro‐Leu‐, ‐Pro‐Gly‐Leu‐, ‐Pro‐Gly‐Phe‐, ‐Pro‐Gly‐Val‐

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150209

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe high‐resolution nmr spectrum of baker's yeast tRNA CUALeu, a recently sequenced non‐denaturable tRNA, has been compared with the spectra of the native and denatured conformers of the closely related species tRNA UUGLeu. Because of the presence of many common base pairs in the different tRNA's, it is possible to assign most of the low‐field resonances to specific secondary‐structure base pairs. A comparison of the observed positions of the various resonances with those predicted by a semiempirical ring‐current shift theory shows a root‐mean‐square deviation of 0.14, 0.11, and 0.12 ppm for tRNA UUGLeu(native), and tRNA UUGLeu(denatured), respectively. These results support the ring‐current shift theory currently used to interpret the low‐field nmr spectra of the tRNA molecules. Differences between the predicted and observed positions of some resonances provide new evidence for higher order effects such as shifts from second nearest neighbors, anomalous shifts exerted by G·U base pairs, and tertiary‐structure effects. A model that was previously proposed for the denatured conformer of

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150210

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe basic theoretical groundwork for the use of derivative binding isotherms in the analysis of ligand binding is presented. The derivative binding isotherm is defined as Γ (Y) =df/dywheref= fractional degree of saturation andy= natural logarithm of the free ligand concentration. Since Γ (y) is a positive function, which goes to zero as y → ±∞, the mean value of y, 〈y〉, and the second and third moments, μ2and μ3about 〈y〉 are well defined.For a macromolecular system consisting ofNequivalent and independent binding sites, Γ (y) is a symmetrical bell‐shaped function with one maximum. The maximum occurs when y = −lnKassoc; μ2= π2/3, and μ3= 0. For multiple sets of independent binding sites, Γ (y) is a superposition of Γ‐type functions. If the sets are sufficiently well separated in binding free energy, multiple extrema may be seen at positions corresponding to the logarithms of the dissociation constants for the individual sets. In any case, 〈y〉 is equal to the mean value of the logarithms of the dissociation constants for the sets; μ2>π2/3 and equal to π2/3 plus the variance of the logarithms of the dissociation constants about their mean value; and μ3is, except by coincidence, not equal to zero and equals the third moment of the distribution of logarithms of the dissociation constants about their mean value.Analysis of Γ(y) for the case of cooperative interactions within a set of binding sites was investigated by examining (1) the Hill model (whose mathematical representation is equivalent to that used to describe antibody heterogeneity except that in the latter case the parametera, the Sips, constant, is constrained (0−4; and μ3= 0. General expressions for the moments in terms of ϕ(f) are derived. In general, μ2(π2/3) for negative for negative cooperativity. Γ(y) will be symmetrical if and only if the

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150211

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

年代:1976

数据来源: WILEY