ISSN:0006-3525    

DOI:10.1002/bip.360230502

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

年代:1984

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360230503

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

年代:1984

数据来源: WILEY

摘要:

AbstractSeveral research groups have studied depolymerizing processes by enzyme cleavage using product distribution. Although only the shortest chain products can be measured experimentally, interpretation of much evidence requires an assumption of the nature of high polymer distribution. The present work analyzes the high polymer distribution of products on the basis of mathematical models suggested for the two most widespread α‐amylase action‐mechanisms. The most‐probable distribution was found to be distorted by hydrolysis only for the shortest chain products. The size of the distorted region is directly dependent on the characteristics of a specific enzyme. We studied the distribution of products for substrates of varying composition to show that it approaches the most‐probable distribution at depolyme

ISSN:0006-3525    

DOI:10.1002/bip.360230504

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe CD spectra of the peptides Boc‐X‐(Aib‐X)n‐OMe (n= 1, 2, 3) and Boc‐(Aib‐X)5‐OMe, where X =L‐Ala orL‐Val have been examined in several solvents. The X = Ala and Val peptides behave similarly in all solvents, suggesting that the Aib residues dominate the folding preferences of these peptides. The decapeptides adopt helical conformations in methanol and trifluoroethanol, with characteristic negative CD bands at 222 and 205 nm. In the heptapeptides, similar spectra with reduced intensities are observed. Comparison with nmr studies suggest that estimates of helical content in oligopeptides by CD methods may lead to erroneous conclusions. The pentapeptides yield solvent‐dependent spectra indicative of conformational perturbations. Peptide association in dioxane results in an unusual spectrum with a single negative band at 210 nm for the decapeptides. Disaggregation is induced by the addition of methanol or water to dioxane solutions. Aggregation of the heptapeptides is less pronounced in dioxane, suggesting that a critical helix length may be necessary to promote association stabilized by helix dipole

ISSN:0006-3525    

DOI:10.1002/bip.360230505

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

年代:1984

数据来源: WILEY

摘要:

AbstractDifferential scanning microcalorimetry was used to investigate the enthalpy (ΔHd) and the temperature (td) of thermal denaturation of normal (nondeuterated) (H‐PC) and deuterated (D‐PC) phycocyanins in D2O solvent. Values oftdin D‐PC are about 5–7°C lower than those in H‐PC. The magnitudes of ΔHdin D‐PC are only 21–32% of those in H‐PC. During the protein unfolding, the heat‐capacity changes (ΔCp) in D‐PC are also lower than those in H‐PC. CD was employed to evaluate the secondary structure and the urea denaturation of these proteins in D2O solvent. These proteins have about the same α‐helix content. D‐PC is less resistant to the denaturant urea than is H‐PC. In general, the apparent free‐energy change in the process of protein unfolding at zero denaturant concentration is higher in H‐PC than in D‐PC. Comparisons of the present results for D2O solvent with those previously reported for H2O reveal that solvent isotope effect essentially does not change the α‐helix content in H‐PC and D‐PC. However, D‐PC or H‐PC has a higher random‐coil content in its secondary structure in D2O than in H2O. Substitution of H2O with D2O as the solvent increasestdin both D‐PC and H‐PC, lowers ΔHdin H‐PC, and greatly lowers ΔHdin D‐PC. The deuterium solvent isotope effect does not change ΔCpin H‐PC but lowers ΔCpin D‐PC. In the urea denaturation, the magnitudes of (Cu)1/2in H‐PC and D‐PC are not affected by such a solvent effect, whereas those of ΔG appsolare greatly increased. The

ISSN:0006-3525    

DOI:10.1002/bip.360230506

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe physical (noncovalent) binding of pyrene and phenanthrene to calf‐thymus DNA in aqueous NaCl solutions was measured by a spectral method (analysis of absorption spectra by Benesi‐Hildebrand plots) and a coupled‐column liquid chromatography method (equilibration of DNA solutions with solid hydrocarbon in a generator column and analysis of dissolved hydrocarbon by liquid chromatography). The measurements yielded values of an affinity constantK′ =nK, wherenis the apparent number of binding sites per nucleotide andKis the apparent binding constant. The affinity of native DNA for pyrene decreases monotonically with increasing NaCl concentration, whereas the affinity of heat‐denatured DNA exhibits a maximum at 0.10MNaCl.K′ for the binding of phenanthrene to native DNA is an order of magnitude lower thanK′ for pyrene. The molar enthalpy for the binding of pyrene to native DNA in 10 mMNaCl is (−34.0 ± 1.0) kJ mol−1. The spectral method data indicate that 50 is an upper limit for the average number of base pairs between intercalation sites for pyrene along the DNA helix and that only a fraction of these sites are bound at the high

ISSN:0006-3525    

DOI:10.1002/bip.360230507

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe viscous forces acting on a DNA macromolecule in a fiber are calculated. The DNA polymer is modeled as an infinite rod of elliptical cross section with a grooved surface. The viscous solvent is hydrodynamic water. Appropriate boundary conditions for determining the viscous forces on the acoustic vibrational modes are discussed. The viscous forces acting on each mode are then calculated as functions of both frequency and amount of water in the fiber. The mass loading of the DNA due to water in the grooves is shown to reduce the longitudinal acoustic velocity, which agrees with recent experimental results. The longitudinal modes are determined to be underdamped and correspondingly sharp over a range of frequencies and humidities appropriate to experimental conditions. The torsional and transverse acoustic modes are still strongly overdamped.

ISSN:0006-3525    

DOI:10.1002/bip.360230508

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe αII‐helix (ϕ = −70.47°, ψ = −35.75°) is a structure having the samenandhas the (standard) αI‐helix (ϕ = −57.37°, ψ = −47.49°). Its conformational angles are commonly found in proteins. Using an improved α‐helix force field, we have compared the vibrational frequencies of these two structures. Despite the small conformational differences, there are significant predicted differences in frequencies, particularly in the amide A, amide I, and amide II bands, and in the conformation‐sensitive region below 900 cm−1. This analysis indicates that αII‐helices are likely to be present in bacteriorhodopsin [Krimm, S.&Dwivedi, A

ISSN:0006-3525    

DOI:10.1002/bip.360230509

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe covalent binding oftrans‐Pt (NH3)2Cl2to the double‐stranded poly(I)·poly(C) follows three types of reactions, depending onrband the concentration of polynucleotide in the reaction mixture. Atrb⩽ 0.1, the principal reaction is coordination to poly(I), giving rise to some destabilization of the double strand, as shown by uv and CD spectra, and a decrease inTmvalues, giving rise to free loops of poly(C). At higherrband low polynucleotide concentration, the free cytidine bases react with platinum bound on the complementary strand to form intramolecular (interstrand) crosslinks that restabilize the double‐stranded structure. At highrband high polynucleotide concentration, while the above reaction still occurs, the predominant one is the formation of intermolecular crosslinks. Under no conditions has strand separation been

ISSN:0006-3525    

DOI:10.1002/bip.360230510

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe fixation oftrans‐(NH3)2Cl2Pt(II) to poly(I)·poly(C) at lowrb(0.075) after reaction with poly(I)·poly(C) but as very minor species. They are formed by reaction with melted poly(I) loops. Also at highrb, we have observed a shifted cytidine H5resonance arising from interaction oftrans‐Pt with a melted loop of poly(C). Most probably, this arises from an intramolecular poly(I) to poly(C) crosslink. Results from the reaction oftrans‐Pt with poly(C) are presented for

ISSN:0006-3525    

DOI:10.1002/bip.360230511

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

年代:1984

数据来源: WILEY