摘要:

Abstract1H,2H,13C, and81Br nmr measurements of mixtures of poly‐L‐lysine hydrobromide with water have been carried out over a range of temperatures and water contents. Whenn(number of molecules of water per residue) ∼13 at room temperature, a transition occurs from a gel to a liquid phase. The liquid phase contains polymer molecules that are flexible, but contain more intramolecular structure than the same molecules in trifluoracetic acid solution. The gel phase contains junction zones of hexagonally packed α‐helices, linked by flexible regions of polypeptide chain. The α‐helical residues impart to their associated water molecules a slight anisotropy of motion, which is dectable by2H nmr. These residues bind up to about seven molecules of water each; the other six required to complete the gel–liquid transition space out the polymer molecules, allowing increased segmental motion of the residues in the flexible regions. This increased motion reduces the energy of the flexible regions and thus increases the proportion of residues in them (increasing the temperature has the same effect); the transition occurs when insufficient residues remain in the α‐helica

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140302

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe Raman spectra of human IgG, IgM, and rabbit IgG in lyophilized form and solution are reported. The spectral results indicate that the predominant structure in these immunoglobulin proteins is the antiparallel β‐sheet. The Raman spectra have also been obtained of rabbit anti‐ovalbumin, and this antibody molecule precipitated with its respective antigen. The spectra reflect a conformational change on binding of antibody with antigen. The conformational change occurs in the direction of disorde

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140303

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

年代:1975

数据来源: WILEY

摘要:

AbstractCopolymers of benzylaspartate with the correspondingpara‐nitro andortho‐nitro derivatives are known to undergo, at increasing nitro content, a transition from a left‐handed α‐helical conformation to a right‐handed α‐helical conformation. The circular dichroism associated with then, π* transition of the amide group, as well as the extrinsic bands associated with the nitrobenzyl chromophore, have been studied for these copolymers as a function of the nitro content. The circular dichroism associated with the 330‐nm extrinsic band is shown to present an abrupt change, which parallels the change in the 222‐nm band characteristic of the left‐ to right‐handed helix transition. The intensity of the 222‐nm CD band seems unaffected by the interaction with the side‐band chromophore. The circular dichroism associated with the 330‐nm band is much stronger in the right‐handed conformation and is unaffected by increasing interactions between side chains. Interpretation in the light of the possible mechanism for optical activity of helical molecules seems to indicate that the 330‐nm extrinsic effect is essentially due to the Condon, Altar, and Eyring (CAE) mechanism and μ‐mperturbation (in Schellmann terminology) on the sid

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140304

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

年代:1975

数据来源: WILEY

摘要:

AbstractUltraviolet circular dichroism spectra have been obtained in aqueous solutions in the presence and absence of ethanol for a synthetic DNA, poly[d(AC):d(GT)], a synthetic RNA, poly[r(AC):r(GU)], and two DNA:RNA hybrids, poly[d(AC):r(GU)] and poly[r(AC):d(GT)]. In the absence of ethanol, we find that the RNA and DNA spectra are dissimilar, while the spectra of the hybrids show differing degrees of similarity to that of the RNA. In the presence of 60–80% ethanol by weight, the spectra of the DNA and both hybrids become much closer to the spectrum of the RNA, which remains relatively unchanged. We interpret the results as indicating that DNA can undergo a change to an A‐type conformation in the presence of ethanol and that the DNA:RNA hybrids are not wholly restricted to an RNA‐like conformation in the absence of et

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140305

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe information that may be obtained from a fluorescence correlation spectroscopic study of a nonideal solution is considered. If all of the macromolecules in a two‐component solution are fluorescently labeled, the mutual diffusion coefficient will be measured. If only a few of the macromolecules in a solution are fluorescently labeled, the tracer diffusion coefficient will be obtained. Two nonideal systems that probably may usefully be studied with fluorescence correlation spectroscopy are proposed. The application of fluorescence correlation spectroscopy to studies of lateral diffusion in biological membranes is discussed; the form of the contribution to the fluorescence correlation spectrum of bulk motion within a membrane is note

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140306

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe enthalpies of transfer, ΔHtr, of a series of amides from water to aqueous solutions of either guanidinium hydrochloride (GuHCl) or potassium iodide were obtained from calorimetric measurements at 25°C. The amides were studied at molalities around 10−2mwhile salt molalities ranged from 0–10m. The amides investigated were Ac‐Gly‐NHMe, Ac‐Gly‐Gly‐NHMe, Ac‐Ala‐NHMe, and Ac‐Leu‐NHMe. Use of an additivity assumption allowed the calculation of group contributions to ΔHtrin these two salt systems for the methyl group, leucyl side chain, and the peptide backbone unit. Values of the entropy of transfer were also obtained. The great ability of GuHCl to randomize protein structures appears to arise from effects on polar and nonpolar groups, which are characterized by enthalpies and entropies of transfer not substantially different from those with KI, a salt comprised of ions of comparable size and polarizability. The difference in the sign of the free energies of transfer of nonpolar groups from water to MX solutions, negative for GuHCl and positive for KI, is the result of these small differences in enthalpies and entropies of transfer. Variations in water structure produced by differences in ionic properties rather than a mode of action for GuHCl very different from that of other salts characterizes its sup

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140307

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe quasi‐elastic light‐scattering (homodyne) time‐correlation functions of calf thymus and λDNA are shown to contain contributions from at least two relaxation processes. A method of asymptotic analysis is described and used to obtain an estimate of the longest relaxation time as well as the “average” relaxation time and the mean‐squared dispersion in this average. Most theories of scattering from macromolecules in the limit of inifinite dilution predict that the longest relaxation time is due to translational self‐diffusion. The data obtained, however, indicate that the longest time is not simply related to the translational self‐diffusion coefficient of unaggregated macromolecules. It is also shown that the longest relaxation time of λDNA decreases in the later stages of the denaturation transition region. Some possible mechanisms for the origin of this long time are discussed, including a model of restricted motion of a molecule

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140308

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe electric birefringence for the aqueous solution of poly‐L‐glutamic acid (PGA) in the helical form was studied. PGA samples were fractionated by gel column chromatography. PGA showed a positive electric birefringence. The permanent dipole moment of the PGA molecule was suggested to be largely suppressed. The measurements of the intrinsic Kerr constants for various molecular lengths showed that the electric anisotropy (polarizability) of PGA is proportional to the 1.5 power of the length. The electric birefrigence measurement was also carried out in the helix–coil transition region. The Kerr constant of PGA was largely reduced on going from the helical form to the coiled

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140309

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe circular dichroism (CD) and absorption spectra of uridine, thymidine, purine ribonucleoside, and the four adenine derivatives 2′‐deoxyadenosine, adenosine, adenosine‐3′,5′‐cyclic phosphate, and arabinosyl adenine were measured in water at pH 7 and pH 2. The absorption and CD spectra of the pyrimidines were simultaneously fitted to four Gaussian bands, and the dipole and rotational strengths of the electronic transitions determined. Adenine‐derivative CD spectra were determined by computer averaging six runs. The spectra showed CD bands at 268, 226, 209, and 195 nm. The band at 226 nm probably is ann–π* transition; the band at 209 nm cannot be detected without a computer. The CD and absorption spectra of purine ribonucleoside indicate three transitions in the 2

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140310

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

年代:1975

数据来源: WILEY

摘要:

AbstractStudies have been made of the precipitation of poly‐L‐glutamic acid from dilute aqueous solutions, over the pH range where the α‐helical conformation is maintained. The major purpose is to establish the molecular conformation in the precipitate and to outline the mechanism of the precipitation. Utilizing molecular‐weight fractions, it is shown that there are two distinctly different precipitation regions, which depend on temperature, concentration, and pH. In one of these regions, the α‐region, a variety of physical properties demonstrate that precipitation occurs without any conformational change. The temperature coefficient of the precipitation process in this region indicates that it is nucleation

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140311

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

年代:1975

数据来源: WILEY