摘要:

AbstractThe association of heparin with thrombin was investigated by fluorometric titration. A maximum of 25% of the fluorescence of fluorescein‐labeled heparin (FTC‐heparin) was quenched at thrombin saturation in the absence of NaCl. FTC‐heparin (H) associated tightly with thrombin (T) and the association constant of the ternary complex, H2T, formed in the absence of NaCl, was calculated to be 1.7 × 108M−1. However, the association was strongly influenced by the NaCl concentration, and the association constant of the equimolar complex, HT, formed in 0.15MNaCl was found to be 1 × 106M−1. The first‐order rate constant,kapp, for inactivation of thrombin by antithrombin III (AT III) and low‐affinity heparin (LA‐heparin) was comparable with that of high‐affinity heparin (HA‐heparin) in the absence of NaCl, but decreased with an increase in the concentration of NaCl. The decreased enhancement of the thrombin‐AT III reaction by LA‐heparin at high NaCl concentration appeared to result from a decreased association of thrombin with LA‐heparin, thus reducing the formation of the ternary complex,

ISSN:0006-3525    

DOI:10.1002/bip.360250402

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

年代:1986

数据来源: WILEY

摘要:

AbstractIntensities of polarized fluorescence from ethidium bound to phage λ DNA undergoing agarose gel electrophoresis were measured. The intensities were strongly field dependent at voltage gradients of 8 V/cm, consistent with a partial orientation of DNA helices in the direction of electrophoresis about 500 times larger than seen in the same field in solution. Such an orientation was predicted by a reptation model of gel electrophoresis advanced by Lumpkin et al. [(1985)Biopolymers,24, 1573–1593]. The present results can be fit successfully to this theory with a single adjustable parameter, the gel–DNA contact distance. Also, λ DNA electrophoretic mobilities in the same concentration gel were determined using the same buffer system. Both orientation and mobility measurements can be fit to the reptation theory within a factor of two using the same values of two parameters, the gel–DNA contact distance and the ratio of DNA charge to frictional coef

ISSN:0006-3525    

DOI:10.1002/bip.360250403

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

年代:1986

数据来源: WILEY

摘要:

AbstractSequences 74–91 and 77–91 ofE. colithioredoxin, which according to x‐ray structure contain an irregular β‐turn, a hairpinlike structural element, have been synthesized and their conformational properties in solution have been investigated by means of CD spectroscopy. In addition, analogs of these sequences, containing the regular β‐turn element Gly‐Pro‐(Gly)2, have also been prepared and investigated. These are BOC‐Ile‐Gly‐Pro‐(Gly)2‐Val‐OMe (III) and BOC‐(Ile)3Gly‐Pro‐(Gly)2‐(Val)5‐OMe (IV) that on the basis of probability, should form hairpin structures stabilized by intramolecular interactions. While the natural sequences were shown to be unable to adopt structures characterized by an intrinsic conformational stability, the two analogs showed evidence of intramolecular folding in methanol and trifluoroethanol–water solution. In particular, the CD spectra are indicative of β‐structure. The most interesting case was observed for compound IV, as the highest degree of conformational order was present in solutions containing a large proportion of water. In addition, the formation of this structure took place in a highly cooperative manner. The results are utilized to discuss whether and to what extent conformationally stable folding peptide units of sm

ISSN:0006-3525    

DOI:10.1002/bip.360250404

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe conformational properties of 5‐fluorouracil derivatives are compared to uracil derivatives. FUrd, 5′‐FUMP, and poly(FU) are studied as a function of pH and temperature by19F‐ and1H‐nmr spectroscopy, and the corresponding uracil derivatives by1H‐nmr spectroscopy. FUrd exhibits no significant conformational changes with solution pH (5–10). In contrast, at low pH (6–7) 5′‐FUMP and 5′‐UMP show similar conformational features, while at high pH (9) 5′‐FUMP shows significant conformational alterations. Also, poly(U) and poly(FU) are conformationally similar at low pH, but increasing pH induces changes in poly(FU). These changes are observed in the backbone [γ(C4′‐C5′)], furanose, and furanose‐base conformations. The apparent pKaof N3‐H ionization of the FUra base is determined by1H‐ and19F‐nmr to range from 7.5 to 8.2 [FUrd<5′‐FUMP<5′‐FUDP

ISSN:0006-3525    

DOI:10.1002/bip.360250405

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

年代:1986

数据来源: WILEY

摘要:

AbstractApplying scanning optical harmonic microscopy to biological tissue for the first time, we have discovered that the macroscopic polarity of rat‐tail tendon is due to a coherent network of discrete polar structures. This finding permits isolation of these structures for further detailed analysis, which should lead to their complete characterization and thus to a solution of the twenty‐year‐old mystery of connective tissue pol

ISSN:0006-3525    

DOI:10.1002/bip.360250406

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe electron‐diffraction pattern of an oriented film of poly(α‐aminoisobutyric acid) in the 310‐helical conformation has been analyzed. The conformation was obtained by a linked‐atom least‐squares refinement of average values from crystal structures. Specimens treated with dichloracetic acid, to improve their crystallinity, conform to space group R3cwitha= 21.8 Å,c= 5.95 Å. The structure contains channels that can accommodate molecules of dichloracetic acid. One molecule of acid per six residues fills the channels, and the R‐factor then is 34% using 23 reflections. Ir evidence is presented to show that the acid may hydrogen bond to the peptide groups. Some reflections occasionally observed on the diffraction photographs are attributed to a 15/4 α‐helix. The significance of the results is considered in relation to Aib‐

ISSN:0006-3525    

DOI:10.1002/bip.360250407

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

年代:1986

数据来源: WILEY

摘要:

AbstractA calculational method developed by G. K. Youngren and A. Acrivos [J. Fluid Mech.75, 377 (1975)] expresses the fluid forces exerted over the surface of an immersed body in terms of differences between body and fluid motions. As opposed to bead‐model approaches, this method starts from an essentially exact hydrodynamic expression, and therefore should be of particular interest to those workers trying to obtain accurate coefficients needed to characterize the diffusive and viscoelastic behavior of macromolecules with complex shapes. However, Youngren and Acrivos's treatment has not been widely adopted nor even used as a proper starting place for higher order bead‐model methods. This is probably related to the unfamiliar appearance of their exact expression, which involves two surface integral terms as opposed to the single summation involved in bead models. We show that their expression may be rewritten in the expected analogous form involving one surface integral term whenever stick boundary conditions are applied to a rigid body or a flexible body composed of rigid segments. For spherical segments, we obtain Rotne–Prager‐type bead‐model results by following typical assumptions. Extensions to deformable particles are considered, in which internal friction can be represented by an arbitrarily viscous inter

ISSN:0006-3525    

DOI:10.1002/bip.360250408

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

年代:1986

数据来源: WILEY

摘要:

AbstractFour different types of ir experiments, involving changes in pH, changes in pressure, and the use of nonaqueous solvents, and with either albumin molecules dissolved in saline or adsorbed albumin films, support the hypothesis that the bandwidth of the amide I vibration of albumin is directly related to the amount of bound water in this protein. From the amide I band narrowing and the amide I shift to higher frequencies, it is proposed that a more ordered helix structure results as the amount of bound water is decreased.

ISSN:0006-3525    

DOI:10.1002/bip.360250409

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe sequential polypeptides (L‐Arg‐X‐Gly)n, where X represents amino acid residues Ala, Val, and Leu, were prepared as models of arginine‐rich histones to be used in studying their structure and their interactions with DNA. The polymerization was carried out on the pentachlorophenyl active esters of the appropriate tripeptides, while the toluene‐4‐sulfonyl group was used for protecting the arginine guanido group. CD was employed to investigate the conformation of (L‐Arg‐X‐Gly)npolymers in aqueous solutions, at different pH, as well as in trifluoroenthanol and hexafluoroisopropyl alcohol solutions. In aqueous solutions (at pH 7 and 12) the prepared sequential polymers behaved as a random coil. The CD spectra in various trifluoroethanol–water or hexafluoroisopropyl alcohol–water mixtures indicated that the degree of helical conformation of the studied polytripeptides increased in the order of Ala → Val → Leu. The opposite was true for the β‐structure. Characteristics of β‐turn are excluded from the poly(L‐Arg‐L‐Leu‐Gly), which assumed the most pronounced helical conformation. The poly(L‐Arg‐L‐Val‐Gly) exerts a significant preference to the β‐turn structure compared to that of poly(L‐Arg‐L‐Ala‐Gly). Thus the probability for helical, β‐structure or β‐turn conformations of the polymers was analyzed in relation to the bulkiness and length, and to the special features of the X‐residue side chain (β‐branching). We concluded that the prepared sequential arginine‐conta

ISSN:0006-3525    

DOI:10.1002/bip.360250410

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe dielectric absorption at millimeter‐wave (mm‐wave) frequencies (50–150 GHz) ofN‐methylacetamide (NMA),N,N‐dimethylacetamide (DiNMA), andN,N‐dimethylacrylamide (DiNMAcry) is measured. Measurements are performed using the oversized‐cavity technique in the temperature range from liquid helium to room temperature. Additionally, a mm‐wave interferometeric measurement at room temperature is made. NMA and DiNMAcry exhibit monotonic increases of the absorption coefficient with temperature as well as with frequency. For DiNMA a monotonic increase of the absorption coefficient with frequency is also found, while the absorption coefficient as a function of temperature shows a pronounced maximum at approximately 30 K. At this maximum the absorption coefficient of DiNMA exceeds those of NMA and DiNMAcry by about two orders of magnitude. The dielectric behavior of the three substances can be described by relaxation processes in asymmetric double‐well potentials. For the low‐temperature relaxation in DiNMA the double well could be established by two possible positions of the molecule in the crystal that are separated by a rotational movement. Hydrogen bonds and long side chains may hinder these relaxational movements in NMA and DiNMAcry, respectively, and thereby account for their comparatively lower absorption. The results are compared with similar results recently obtained on proteins and sy

ISSN:0006-3525    

DOI:10.1002/bip.360250411

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

年代:1986

数据来源: WILEY