摘要:

AbstractThe adsorption of globular proteins at solid/liquid or liquid/liquid interfaces provides evidence of unfolded molecular conformation. Proteins with high apolar character are strongly unfolded, while those with high polar character are generally incompletely unfolded. Structural changes of globular proteins at adsorption on mercury electrodes were studied by ac polarography and capacity–time curves. The surface area per molecule of nine globular proteins was determined from the adsorption kinetics at the dropping mercury electrode. For all the proteins investigated, this value was greater than the maximal molecular cross section of the native proteins. The surface area was about 19 Å2per amino acid residue, which coincides with the value for unfolded proteins at the water/air interface. Differences between dropping mercury electrode and hanging drop mercury electrode occurred only with lysozyme and phosphorylase; for the other proteins, the structure of the adsorption layer was independent of the time of interaction at the electrode. Since not all of the reducible groups of the adsorbed proteins come into contact with the electrode, the flattening should be incomple

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140802

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

年代:1975

数据来源: WILEY

摘要:

AbstractConformational analysis ofN‐methylamide of pyroglutamic acid has been performed by theoretical energy calculations and experimental physical techniques, namely, laser Raman spectroscopy and depolarized Rayleigh scattering. The two theoretically predicted conformations are evidenced in crystalline state (ψ1= +169°) and in aqueous solution (ψ1≃ −20°). This study confirms the interest of a careful vibrational analysis of peptides andN‐deuterated derivatives for providing an estimate of the dihedral angle ψ. The relationship between amide III frequency and ψ values

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140803

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe structure of β‐chitin has been refined by rigid‐body least‐squares methods, based on the intensity data for highly crystalline specimens from the pogonophoreOligobrachia ivanovi. The structure consists of an array of poly‐N‐acetyl‐D‐glucosamine chains all having the same sense, which are linked together in sheets by NH … OC hydrogen bonding of the amide groups. In addition to the O‐3′H … O‐5 intramolecular hydrogen bond, analogous to that in cellulose, the CH2OH side chain forms an intrasheet hydrogen bond to the carbonyl oxygen on the next chain. This structure shows considerably better agreement between observed and calculated intensities than that possessing an intersheet hydrogen bond, as had been proposed previously. The structure is consistent with the swelling properties of β‐chitin and can also be seen to be anal

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140804

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

年代:1975

数据来源: WILEY

摘要:

AbstractClassical potential energy calculations have been made for the ribodinucleoside monophosphates ApA, CpC, GpG, and UpU. Van der Waal's, electrostatic, and torsional contributions to the energy were calculated, and the energy was minimized with the seven backbone conformational angles as simultaneously variable parameters. At the global minimum, ApA and CpC have conformations like double helical RNA: the angles ω′ and ω areg−g−, the sugar pucker is C3′‐endo, and the bases areanti. GpG and UpU, on the other hand, have the ω′,ω angle pairg−tat the global minimum, and for GpG the bases aresyn. Energy contour maps for ω′ and ω show two broad, low energy regions for ApA, CpC, and UpU: one isg−g−, and the second encompassesg−tandg+g+within a single lowenergy contour. The two regions are connected by a path at 10–13 kcal./mole. For GpG, with basessyn, however, only a small low‐energy region atg−tis found. The helical ‘A’ RNA conformation is 8.5 kcal/mole higher for this molecule. Thus, the base composition is shown to influence the conformations adopted by dinucleoside phosphates. Comparison of calculations with experimetal data,

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140805

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe far infrared spectra of poly(L‐proline) I (190–35 cm−1) and II (400–35 cm−1) were obtained in the solid state at both 300° and 110°K. A significant difference in the region below 100 cm−1was observed. A very intense band located at 60 cm−1in the infrared spectrum of form II has no counterpart in form I. This indicates the sensitivity of low‐frequency vibrations to the difference in conformation assumed by both forms in the solid state.Additional bands observed in this study are correlated with ir and Raman data previously reported and tentative assignments are made using the results of normal mode calculations (in the single‐chain approximation) which

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140806

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

年代:1975

数据来源: WILEY

摘要:

AbstractPotentiometric titrations of poly(S‐carboxymethyl‐L‐cysteine) and poly(S‐carboxy‐ethyl‐L‐cysteine) were carried out in aqueous sodium chloride solutions and in water. For samples of both polymers of high molecular weight, a new pattern was observed concerning the change of titration curve with time; the β‐coil transition became sharper and the transition free energy increased by about 100 cal mole−1as the equilibrium was approached. This suggests that equilibrium data were not obtained in most previous studies on the titration involving the β‐coil transition. It also shows that the reversbility is not necessarily sufficient to confirm the equilibrium. Another pattern, which was previously observed, was also confirmed with a low molecular weight sample of poly(S‐carboxymethytl‐L‐cysteine). The titration curves were shown to be insensitive to polymer concentration, even when aggregation or phase separation was present. The validity of the Gouy model to describe the titration curve of the β‐structure was found to depend on molecular weight as well as o

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140807

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

年代:1975

数据来源: WILEY

摘要:

AbstractA series of copolymers ofL‐lysine andL‐valine [poly(L‐lysinefL‐valine100‐f)] containing 0–13%L‐valine have been studied, in 0.10MKF solution, using potentiometric titration and circular dichroism spectroscopy. Incorporation of increasing amounts of valine into the copolymers favors β‐sheet formation over α‐helix formation at high pH and room temperature. The titrations were analyzed using the method of Zimm and Rice and the partial free energy (ΔG0cβ) for the coil‐to‐β‐sheet transition for valine is estimated at 900 cal/mole at 25°C. From the temperature dependence of the free energy, the partial enthalpy, ΔH0cβ, and entropy, ΔS0cβ, of the transition for valine is estimated to be 854 cal/mole and 6.0 e.u., respectively. The corresponding partial thermodynamic parameters forL‐lysine are in agreement with published results. The fraction of β‐sheet versus pH has been calculated for poly(L‐lysine86.8L‐valine13.2) at 25.0°C using the titration data; data obtained from circular dichroism spectroscopy for the same copolymer are in good accord. It is concluded from these results thatL‐valine is a very strong β‐sheet forming amino acid. Furthermore, these results indicate that the Zimm–Rice method is applicable to transitions between the coil and β‐sheet state

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140808

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

年代:1975

数据来源: WILEY

摘要:

AbstractThree kinds of fluorescence enhancement result from the interaction of 2‐p‐toluidinylnaphthalene‐6‐sulfonate and calf‐skin collagen. They are negatively cooperative, independent, and highly cooperative fluorescence enhancement. In the independent region at pH 3.7, the binding number is about 36 moles of 2‐p‐toluidinylnaphthalene‐6‐sulfonate per mole of tropocollagen with a binding constant of 2.0 × 104M−1; with ΔG= −5.7 kcal/mole, ΔH= −4.0 kcal/mole, and ΔS= 6 e.u. The pH dependence of fluorescence of native collagen shows that the deprotonated forms of the β and γ carboxyl groups of aspartic and glutamic acid decrease the intensity, possibly by charge repulsion of the negatively charged sulfonate group of 2‐p‐toluidinylnaphthalene‐6‐sulfonate. The positive charge of lysine is found to be unimportant in the interaction of 2‐p‐toluidinylnaphthalene‐6‐sulfonate with collagen. Fluorescence enhancement is caused mainly by the hydrophobic interactions of 2‐p‐toluidinylnaphthalene‐6‐sulfonate and collagen. Salt bridge formation between basic and acidic side chains in very low salt concentration may be detectable

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140809

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

年代:1975

数据来源: WILEY

摘要:

AbstractConformational analysis of double‐stranded helical polynucleotides was carried out in terms of internal and external parameters, using semiempirical energy potential functions. The results obtained show that the structures proposed on the basis of the X‐ray analysis for A‐DNA and RNA's are almost identical to those corresponding to the conformational energy minima, whereas that proposed for B‐DNA still appears to suffer from conformational strains. On the other hand, the B‐DNA structure theoretically predicted is stabilized by both van der Waals energy and possible specific interactions with water molecules and counterions. This may explain the stability of the B form with respect to the A form at high relative humidity and ion strength. A possible role of the A + T fraction in stabilizing the B‐type DNA emerges in connection with its preferential ability to bind ions. This agrees with the results on the crystalline structures of GpC and ApU. For RNA's, the occurrence of only A‐type structures is explained as being due to the C(3′)‐endopuckering of ribose

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140810

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

年代:1975

数据来源: WILEY

摘要:

AbstractA very general approach to the chemical equilibria between many interacting molecules during sedimentation (boundary, band, or active enzyme) taking into account boundary conditions, cell geometry, equilibrium constants, diffusion, enzyme kinetics, etc., is presented. Through a Fortran program, the method has been applied to two very simple but typical cases. With only minor adjustments, the method presented here for sedimentation studies can be extended to all sorts of problems in which “pools” of various species are interacting with each ot

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140811

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

年代:1975

数据来源: WILEY