摘要:

AbstractRaman spectra of DNA from calf thymus DNA have been taken over a wide range of temperatures (25°–95°) in both D2O and H2O. A study of the temperature dependence of the Raman spectra shows that the temperature profiles of the intensities and frequencies of the various bands fall into four different categories: (1) base bands that show a reversible increase in intensity prior to the melting region, i.e., a definite premelting phenomenon; (2) base bands that show little or no temperature dependence; (3) deoxyribose‐phosphate backbone vibrations that show no temperature dependence up to the melting region, at which point large decreases in intensity occur; and (4) slow frequency changes in certain in‐plane vibrations of guanine and adenine due to deuteration of the C‐8 hydrogen of these purines in D2O.Certain Raman bands arising from each of the four bases, adenine, thymine, guanine, and cytosine have been found to undergo a gradual increase in intensity prior to the melting region at which point large, abrupt increases in intensity occur. The carbonyl stretching band of thymine, involved in the interbase hydrogen bonding actually undergoes both a gradual shift to a lower frequency as well as an increase in intensity. These changes provide evidence that some change in the geometry of the bases relative to each other begins to occur around 50°C, well below the melting region of 70°–85°C.From the spectra taken at various temperatures, the DNA appears to remain in the B conformation until the melting point is reached, at which time the DNA progresses into a disordered random‐coil form. No A‐form conformation is found either in the premelting or

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140202

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

年代:1975

数据来源: WILEY

摘要:

AbstractPurified potato starch, cross‐linked with epichlorohydrin (65–5.4 anhydroglucose units per cross‐link) by an iterative method that preserved the native crystalline structure of the starch granule, was exposed to enzymic (B. subtilisα‐amylase at 50°C) and acidic (3NHCl at 40°C) hydrolysis. The stability of the granules to digestion by enzymes, as measured by their weight loss after incubation with the enzyme solution, increased with the degree of cross‐linking; by contrast, the stability to acid attack decreased as a function of the degree of cross‐linking. The morphology of these samples was studied by scanning electron microscopy. A lamellar structure, which was most evident after enzyme treatment, was observed in samples that had a weight loss of greater than 50%. The results reflect differences in accessibility, which are interpreted in terms of a statistical model of the ultrastructure with correlated fluctuations in density in the ra

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140203

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe broadening of a helix–coil transition due to base pair heterogeneity is calculated on the basis of a cumulant perturbation expansion in the quasi‐grand ensemble. In this ensemble the fictitious, homogeneous chain, to which the perturbation is referred, automatically decreases its correlation length as the heterogeneity increases. This “renormalization” seems to stabilize the perturbation expansion, in view of the good agreement between the present results and the exact theory of a heterogeneous polypeptide helix–coil transition. For the DNA model in which ring entropy is included, the transitions is found to be extremely narrow for an infinite random chain with conventional parameters. A tentative reconciliation of this result with contradictory calculations of some other workers is offered on the basis of end effects, coarse graining, or approximation to the ring entropy. An application of the new method to DNA with a non‐random base pair distribution requires evaluation of the correlation function between molecular states (helix or coil), at different sites of the reference chain. The evaluation is reduced to quadrature, but numerical calculations have been made only for the r

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140204

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe conformation of single‐stranded polyrA in aqueous solution has been measured at temperatures down to −12°C. The radius of gyration of low‐molecular‐weight polyrA varies very little with temperature in this range. By studying the dependence of radius of gyration on temperature for several polyrA fractions, we show that the dependence of the radius upon chain length is consistent with formation of a single‐stranded rodlike structure at low temperature. The structure has an approximate length of 3.2 Å

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140205

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe growth of the weight‐average double‐strand length of renaturing sonicated DNA was investigated as a function of the degree of renaturation. Endonuclease S1 was used to digest single‐strand ends and gaps. The ratio of the average renatured length to the initial length was found to be 0.6 ± 0.1 early in the reaction and to approach 1.0 at infinite time, while the ratio of the average single‐strand length of native regions increased from 0.6 ± 0.1 to 0.8 ± 0.1 at infinite time. The ratio increases are nonlinear, with the greatest growth occuring around 50% renaturation. Relaxation times of double‐strand DNA were measured in low salt using alternating field electric birefringence and were found to increase to only 70% of the relaxation time of the initial DNA at infinite time. In the molecular‐weight range examined (150–320,000 daltons), relaxation times vary with the 2.3 ± 0.3 power of

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140206

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe properties of apomyoglobin were examined in aqueous solutions and various helix‐ and random‐coil‐forming solvents by solvent perturbation, optical rotation, circular dichroism, and viscosity measurements. The solvent perturbation data obtained in neutral aqueous solutions suggest 25–40% exposure of the two tryptophyl residues and 50–60% exposure of the three tyrosyls. The estimates of burial of these groups are in the ranges expected for myoglobin based on its X‐ray structure. In the helicogenic alcohols, methanol, ethanol, 2‐chloroethanol, trifluoroethanol, and 1‐propyl alcohol, as well as in acidic solutions, 8Murea and 6Mguanidine hydrochloride, essentially all the tryptophyl and tyrosyl residues are found to be exposed to solvent based on this method. Analysis of the ORD and CD data indicates that in the alcohols the α‐helix content of apomyoglobin has in most cases changed from 58–59% to about 80–95%. Analysis of the intrinsic viscosity data based on the equations of Simha and Kirkwood and Auer indicates that the polypeptide chain in these solvents has the dimensions of fully extended α‐helical rods, with lengths of 221–251 Å and mean diameters of 12.8–13.6 Å. It is concluded that apomyoglobin in the various alcohols must have an extended but somewhat irregular rodlike structure, having a few bend or irregular sequences between the α‐helical segments due largely to the presence of the four proline residues, 37, 88, 100,

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140207

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe fluorescence parameters, lifetime, relative quantum yield, maximum and mean wavelength, half‐width, and polarization, of bovine serum albumin (BSA) were measured at 15°C in aqueous solutions containing varying concentrations of different chemical perturbants, glycerol, Cu2+ions, guanidine hydrochloride, and urea. By considering a quenching mechanism as being either dynamic or static, depending upon whether the quenching is or is not accompanied by a change in the fluorescence lifetime, we were able to correlate the changes produced in the various fluorescence parameters by the different chemical perturbants with changes in macromolecular structure as the concentration of perturbant was gradually increased. The addition of glycerol and of Cu2+ions indicated that in aqueous BSA both tryptophan residues are below the surface of the macromolecule, out of contact with solvent water, and, as a consequence, they are statically quenched. “Ultra‐Pure” guanidine hydrochloride at 2.4Mor more caused a drastic conformation change, which resulted in the emergence of a visible tyrosine peak at 304 nm in the BSA fluorescence spectrum when either 260‐ or 270‐nm excitation was employed. With the same excitation, the enhancement of BSA tyrosine fluorescence by 6–8Multra‐pure urea produced only a shoulder near 304 nm in the BSA fluorescence spectrum. We have introduced the use of a new relative quantum yield for protein fluorescence,q′, referenced to the quantum yield of unquenched free tryptophan, which eliminates the quenching action of water

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140208

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

年代:1975

数据来源: WILEY

摘要:

AbstractPoly‐β‐1‐naphthylmethyl‐L‐aspartate and copolymers of β‐1‐naphthylmethyl‐L‐aspartate and γ‐benzyl‐L‐glutamate were prepared. From the results obtained by a study of infrared and circular dichroism spectra, poly‐β‐1‐naphthylmethyl‐L‐aspartate was found to be a left‐handed α‐helix both in the solid state and in solution. The fluorescence spectra of these polymers showed excimer emission of the naphthyl chromophores and gave some information about the arrangement of the side‐chain chromophores. By optical titration experiments, it was found that an increasing amount of β‐1‐naphthylmethyl‐L‐aspartate residues in the copolymers induc

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140209

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe Raman spectrum of poly‐DL‐alanine (PDLA) in the solid state is interpreted in terms of the disordered chain conformation, in analogy with the spectrum of mechanically deformed poly‐L‐alanine. The polymer is largely disordered with only a small α‐helical content in the solid state. When PDLA is dissolved in water, the spectra suggest that short α‐helical segments are formed upon dissolution. These helical regions might be stabilized by hydrophobic bonds between side‐chain methyl groups. Addition of methanol to the aqueous PDLA solutions results in a Raman spectrum resembling that of solid PDLA. This result suggests that the methanol disrupts the helical regions by breaking the hydrophobic bonds.The Raman spectra of poly‐DL‐leucine (PDLL) and poly‐L‐leucine (PLL) are compared and only slight differences are observed in the amide I and III regions, indicating that PDLL does not have an appreciable disordered chain content. Significant differences are observed in the skeletal regions. The 931‐cm−1lines in the PLL and PDLL spectra are assigned to residues in α‐helical segments of the preferred screw sense, i.e.,L‐residues in right‐handed segments andD‐residues in left‐handed segments (in PDLL). On the other hand, the 890‐cm−1line in the spectrum of PDLL is assigned to residuesnotin the preferred helical sence, i.e.,L‐residues in left‐handed segments andD‐residues in right‐handed ones. The Raman spectra of poly‐DL‐lysine and poly‐L‐lysine in salt‐free water at pH 7.0 are compared. The Raman spectra of the two polymers are very similar. However, this does not negate the hypothesis of local order in poly‐L‐lysine because the distribution of the residues in poly‐DL‐lysine probably ten

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140210

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe Raman spectra of collagen, gelatin, and elastin are presented. The Raman lines in the latter two spectra are assigned by deuterating the amide N‐H groups in gelatin and by studying the superposition spectra of the constituent amino acids. Two lines appear at 1271 and 1248 cm−1in the spectra of collagen and gelatin that can be assigned to the amide III mode. Possibly, the appearance of two amide III lines is related to the biphasic nature of the tropocollagen molecule, i.e., proline‐rich (nonpolar) and proline‐poor (polar) regions distributed along the chain. The melting, or collagen‐to‐gelatin transition, in water‐soluble calf skin collagen is studied and the 1248‐cm−1amide III line is assigned to the 31helical regions of the tropocollagen molecule.Elastin is thought to be mostly random and the Raman spectrum confirms this assertion. Strong amide I and III lines appear at 1668 and 1254 cm−1, respectively, and only weak scattering is observed at 938 cm−1. These features have been shown to be characteristic of the disordered con

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140211

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

年代:1975

数据来源: WILEY