摘要:

AbstractThermally induced helix–coil transitions of myosin rod, light meromyosin, and tropomyosin were studied by optical rotatory dispersion (ORD). Fractional helicity was calculated from both the Moffitt‐Yang parameter,b0, and the corrected mean residue rotation [m′] at 231.4 nm. Between 3 and 30°C, [m′] increases linearly with a slope of 59/°C, whereasb0is virtually constant, indicating apparently different thermal melting behavior. Poly(L‐lysine) and poly(L‐glutamic acid) in their helical forms and myoglobin also show a nearly linear temperature dependence of [m′]231.4. Muscle proteins in 6Mguanidine hydrochloride and the random‐coil forms of the homopolymers exhibit temperature‐dependent values of [m′]231.4andb0. We conclude from these observations that ORD properties of both α‐helices and random‐coil polypeptides have significant intrinsic temperature dependencies. A new method of estimating fractional helicity as a function

ISSN:0006-3525    

DOI:10.1002/bip.360240902

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe confortmational behavior of the cholecystokinin‐related fragments CCK4, CCK5, and CCK6as determined by1H‐nmr spectroscopy in DMSO‐d6and water and fluorescence‐transfer measurements in aqueous medium are greatly dependent on the ionization states of these peptides. Under netral conditions, the backbones of CCK5and CCK6preferentially adopted folded forms with a β‐turn including the four residues Gly‐Trp‐Met‐Asp, probably stabilized by a hydrogen bond between the CO of Gly and the NH of Phe. In these structures, possible induced by an ionic interaction between the carboxylic group of Asp32and the NH 3+group of the N‐terminal amino acid, the lateral chains of the various residues are quite distant from each other (15–16 Å). Under acidic conditions, extended structures without interactions between side chains predominate for CCK5and CCK6, while for CCK4, a conformational change drawing the Trp and Phe side chains in close proximity was shown by fluorescence. The conformations observed in aqueous medium at physiological pH are discussed in relation to the biological act

ISSN:0006-3525    

DOI:10.1002/bip.360240903

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe glycoprotein mucin was isolated from the sputum of patients with chronic obstructive bronchitis. The fractionation procedure included treatment with 6Murea at pH 12.5 followed by gel filtration in 6Murea at neutral pH. (1) Using a low‐shear Cartesian diver viscometer, we found that the mucin intrinsic viscosity equals (0.32 ± 0.03) L/g in 1000 mMNaCl solution increasing to (12 ± 3) L/g in 0.1 mMNaCl (pH 7 and 20°C). (2) The relaxation of electrically induced birefringence in mucin solutions was measured and the relaxation spectrum calculated using a Fourier‐transform deconvoltion method. We found that the dominant relaxation time increased from 1 to 150 μs when the exitation pulse duration used was increased from 2 to 300 μs. (3) Mucin was vacuum‐dried from glycerol‐containing solutions followed by low‐angle rotary shadowing and electron microscopy. Mucin was found to be unbranched, with contour lengths ranging from 300 to 2500 nm and with an average of 900 nm. Our result indicate that mucin is an extended and flexible molecule with Kuhn length 0.3–0.5% of th

ISSN:0006-3525    

DOI:10.1002/bip.360240904

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

年代:1985

数据来源: WILEY

摘要:

AbstractA model has been developed for approximating the free energy of collagen fibril formation (ΔFf) and the equilibrium solubility of collagen under physiological conditions. The model utilizes an expression of Flory for rodlike polymers, with the modification that the “pure” anisotropic phase is defined as a collagen fibril containing about 0.3 g water/g collagen. The model also assumes that χ1, the polymer–solvent interaction term, is entirely due to hydrophobic effects. χ1is estimated from hydrophobic bond energies of amino acid side chains, using the results of Némethy and Scheraga. The temperature dependence of χ1is utilized to calculate equilibrium solubilities and ΔFfas a function of

ISSN:0006-3525    

DOI:10.1002/bip.360240905

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

年代:1985

数据来源: WILEY

摘要:

AbstractA combination of novel methods of macrostructural analysis and theoretical chemistry were applied to study the metalloenzyme carboxypeptidase A and its complexes with two inhibitors—glycyl‐L‐tyrosine and a protein inhibitor isolated from potatoes. The methods of macrostructural analysis applied to the study of the crystal structures of these molecules include structural superposition, distance matrix analysis, and linear distance plot analysis, and the approach is complemented by the examination of computed physicochemical properties, including electrostatic potential surfaces, bulk hydrophobicity, and complementarity of van der Waals surfaces. The structural analysis identified folding domains in carboxypeptidase A that relate to such domains in carboxypeptidase B and are involved in the conformational changes following complexation with the inhibitors. The nature of these conformational changes and their relation to the physicochemical properties suggest their role in determining recognition and reactivity characteristics of the enzyme. The analysis also revealed a distinction between conformational changes in the secondary and tertiary structure of the protein that provides insight into the structure–function relationship in carboxypeptidase. Notably, some inhibitor‐induced changes in structure occur in regions in which the interacting molecules are not in contact, while some of the contact regions, such as the active site, incur only minor perturbation. The analysis reveals the interrelation between the enzyme–ligand interaction and the structural perturbation outside the active site, thus illuminating one aspect of the link between the structural organization of the protein and i

ISSN:0006-3525    

DOI:10.1002/bip.360240906

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe preferred conformations ofN‐acetyl‐N′‐methyl amides of some dialkylglycines have been determined by empirical conformational‐energy calculations; minimum‐energy conformations were located by minimizing the energy with respect to all the dihedral angles of the molecules. The conformational space of these compounds is sterically restricted, and low‐energy conformations are found only in the regions of fully extended and helical structures. Increasing the bulkiness of the substituents on the Cα, the fully extended conformation becomes gradually more stable than the helical structure preferred in the cases of dimethylglycine. This trend is, however, strongly dependent on the bond angles between the substituents on the Cαatom: In particular, helical structures are favored by standard values (111°) of the N‐Cα‐C′ angle, while fully extended conformations are favored by smaller values of the same angle, as experimentally observed, for instance, in the case of

ISSN:0006-3525    

DOI:10.1002/bip.360240907

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe dynamic behavior of pig immunoglobulin G in deuterium oxide solutions was investigated by the neutron spin‐echo technique. This novel technique makes it possible to study intramolecular motion without introducing probes into the macromolecule. Using neutron spin‐echo, the effective diffusion coefficient,Deff, was obtained as a function of the transferred momentum, κ. For interpretation of the experimental data, two models were designed, and computedDeffvalues were compared with experimental data. The rigid T‐shape model was compatible with the experimental data only by assuming an unrealistically high rotational diffusion coefficient, and it was therefore unacceptable. Reasonable agreement with all available experimental data was obtained with a flexible model of immunoglobulin G molecule, which the Fab arms are assumed to wobble around the hinge region within an angle

ISSN:0006-3525    

DOI:10.1002/bip.360240908

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe viscoelastic properties of solid samples (crystals, amorphous films) of hen egg white lysozyme, bovine serum albumin, and sperm whale myoglobin were studied in the temperature range of 100–300 K at different hydration levels. Decreasing the temperature was shown to cause a steplike increase in the Young's modulus of highly hydrated protein samples (with water content exceeding 0.3 g/g dry weight of protein) in the temperature range of 237–251 K, followed by a large increase in the modulus in the broad temperature interval of 240–130 K, which we refer to as a mechanical glass transition.Soaking the samples in 50% glycerol solution completely removed the steplike transition without significantly affecting the glass transition. The apparent activation energy determined from the frequency dependence of the glass‐transition temperature was found to be 18 kcal/mol for wet lysozyme crystals. Lowering the humidity causes both the change of the Young's modulus in response to the transition and the activation energy to decrease. The thermal expansion coefficient of amorphous protein films also indicates the glass transition at 150–170 K. The data presented suggest that the glass transition in hydrated samples is located in the surface layer of proteins and related to the immobilization of the protein groups and strongly bo

ISSN:0006-3525    

DOI:10.1002/bip.360240909

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

年代:1985

数据来源: WILEY

摘要:

AbstractWe have studied the structure of solid films obtained by x‐ray diffraction, from several basic polypeptides with a defined sequence. The alterating polypeptides poly(Ala‐Lys), poly(Leu‐Lys), poly(Val‐Lys), and poly(Arg‐Leu) all show a cross‐β‐structure in which layers of hydrophilic side chains alternate with layers containing hydrophobic side chains. The other polypeptides studied are not in the β‐conformation and appear to be in the α‐helical conformation. The helices obtained from poly(Lys‐Ala‐Ala) and poly(Lys‐Ala‐Ala‐Lys) appear to be packed in an unusual fashion, which favors interaction between alanine side chains. Such behavior is

ISSN:0006-3525    

DOI:10.1002/bip.360240910

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

年代:1985

数据来源: WILEY

摘要:

AbstractA unified representation of helical parameters (n,h) based on a polar mapping is proposed. Its application to the case of polysaccharides allows a straightforward comparison of all secondary structures displayed by this class of biopolymers in the solid state. Based on the concept that a disordered state of a polymer may be described by a succession oflocalhelical parameters, the application of this unified representation has been extended to the simulation of chain behavior in solution.

ISSN:0006-3525    

DOI:10.1002/bip.360240911

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

年代:1985

数据来源: WILEY