摘要:

AbstractWe obtain an analytical solution for the binding of 2‐site ligands to a heterogeneous lattice. The model also describes the kinetics of chemical reactions between adjacent pendant groups of a copolymer. Our analysis is based on theprinciple of independence, as formulated by Gonzalez and Hemmer. Several special cases are solved in closed form; a power series solution is developed for the general problem. The results may be modified to take into account fixed total ligand. We also analyze competition between 1‐site and 2‐site ligands. As an illustration of the results, we examine in detail the kinetics and final extent of binding for two special

ISSN:0006-3525    

DOI:10.1002/bip.360291002

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

年代:1990

数据来源: WILEY

摘要:

AbstractWe have studied the net positive charge distribution in the C‐terminal region of histone H1. We find that it is not random, but rather uniform. In most histone H1 sequences, 4 ± 1 positive charges are found in this region of the molecule in over 95% of all possible segments that are 10 amino acids long. Neither alternating sequences (basic–;nonbasic) nor more complex repeating sequences are ever found. Clusters of three or more basic amino acids are seldom observed in somatic H1s, yet their presence increases in sperm histones and even more so in protamines. It is concluded that the C‐terminal region of histone H1 has a remarkably uniform distribution of charge, in spite of its apparent variactions in sequence in different proteins and within individual molecules. The functional significance of these findings is discussed, suggesting a purely electrostatic role for the C‐terminal region of histone H1, which may be evenly wrapped around individual segments of DNA molecules, thus decreasin its net charge. A likely candidate for a long α‐helical region in the C‐terminal region of histone H1 from sea urchin spermatozoa also has been located. This region may contribute to the aggregating properties of this histone in sp

ISSN:0006-3525    

DOI:10.1002/bip.360291003

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe linear viscoelastic and rheological properties of high molecular weight ovine submaxillary mucin (OSM) solution have been investigated in terms of the Newtonian steadyflow viscosity\documentclass{article}\pagestyle{empty}\begin{document}$ [\eta (\dot{\gamma})] $\end{document}, the complex oscillatory viscosity [η*(ω)], and the storage and loss shear moduli [G′(ω) andG″(ω)]. It was observed that\documentclass{article}\pagestyle{empty}\begin{document}$ \eta (\dot{\gamma}) $\end{document}, η*(ω), andG′(ω) are always higher when OSM is dissolved in 0.1MNaCl than when at the same concentration in 6MGdnHCl. This is consistent with previous observations that submaxillary mucins self‐associate in 0.1MNaCl to form large aggregates, which are disrupted in 6MGdnHCl. As the OSM concentration increases, the appearance of a plateau shear modulus indicates the formation of a gel network in both solvents. The results suggest gelation involves specific intermolecular interactions, perhaps due to hydrophobic forces between interdigitated oligosaccharide side chains. The viscoelastic behavior of OSM solution at high concentration is thus similar to that reported in the literature for porcine gastric mucin (PGM). However, the OSM gels are mechanically weaker, having moduli that are an order of magnitude lower thatn those for PGM gels of comparable concentration. The oligosaccharide side chains of OSM consist of only 1–2 sugar units compared to 10–15 for PGM, but it appears that this is sufficient to allow for intermolecular interaction and the form

ISSN:0006-3525    

DOI:10.1002/bip.360291004

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe elctric potential around the alanyl dipeptide in various conformations was calculated from ab initio 6–31G wave functions. Seven conformations were selected to correspond to calculated local energy minima of the isolated molecule. Five additional conformations were selected corresponding to the alanylalanine crystal structure and the polypeptide conformations in a right‐handed α‐helix, left‐handed α‐helix, parallel β‐sheet, and anti‐parallel β‐sheet. The electric potential surrounding each conformer was fitted with either net charges at atomic sites or dipolles at bond sites by least squares. Either choice reproduced the electric potential with relative rms deviations of 1.9–4.8%. Values for net atomic charges or bond dipoles were usually in line with expectations based on electronegativity. The imino and carbonyl groups showed their expected polarities, although there were considerable deviations from zero group charge. Net atomic charges on and near the α‐carbon changed substantially with the conformation angles; bond dipoles around the α‐carbo

ISSN:0006-3525    

DOI:10.1002/bip.360291005

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe three‐dimensional structure of a cyclic bouvardin analogue, cyclo (‐Pro‐MeTyr‐Ala‐MeTyr‐MeTyr‐D‐Ala‐) has been determined by distance geomtry calculation and restrained energy minimization from nmr data. The preparation of the input for the distance geometry calculations, the modification of the amino acid library, and the analysis of the structures were done with the aid of a recently developed software package, GEOM. A great variety of different initial structures were explored to check the uniqueness of the determined solution structure. Calculations with 500 different initial structures and two different strategies led to a uniquely determined backbone conformation with a root mean square deviations value of 0.4 Å. The backbone structure consists of two β‐turns, a β‐II turn at Pro1‐MeTyr2, and a β‐VI turn at MeTyr4‐MeTyr5. The efficiency of the two calculation strategies were compared in order to propose an optimal means for performing distance geometry calc

ISSN:0006-3525    

DOI:10.1002/bip.360291006

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe stability, metastability, and instability regions of aqueous solutions of a representative synthetic bioelastomeric polymer, poly (Val‐Pro‐Gly‐Val‐Gly), were determined by a combined used of elastic and quasi‐elastic light scattering experiments. The approach followed here offers the attractive advantage of singling out the relevant contributions to the total scattering even in the presence of traces of noninteracting larger sized impurities. Conclusions so reached were checked by means of independent experiments. The present results provide descriptions of the very early events in the physics of bioelastogenesis in terms of general polymer science and phase transitions, and in terms of an unexpected possible functional role of density flu

ISSN:0006-3525    

DOI:10.1002/bip.360291007

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

年代:1990

数据来源: WILEY

摘要:

AbstractLangevin modes described the behavior of atoms moving on a harmonic potential surface subject to viscous damping described by a classical Langevin equation. We present applications to the protein crambin and to the DNA duplex d(CpGpCpGpCpG)2and its complex with ethidium. Our friction matrix is weighted according to surface area exposed to solvent, and results are reported for various values of the solvent viscosity and models for hydro‐dynamic interactions. Even for relatively small solvent friction (η = 0.3 cp) a substantial number of modes are overdamped, and time correlation functions decay smoothly without the oscillations characteristic of gas‐phase calculations. Perturbation theory starting from the gas‐phase modes is accurate for many low‐frequency modes (which are overdamped in the presence of solvent), but fails badly for higher modes. For correlation functions of interest to fluorescence depolarization or nmr relaxation, the plateau values are insensitive to solvent viscosity, but the relaxation times are not. The advantages and limitations of this analysis of macromolecular motions are d

ISSN:0006-3525    

DOI:10.1002/bip.360291008

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

年代:1990

数据来源: WILEY

摘要:

AbstractChemical shift data have been collected on eight proteins that have the same conformation in solution as in their crystal structures. Ring‐current shifts have been calculated and subtracted from the experimentally measured shifts, to leave shifts that depend only on local conformation. Overall, the shifts show an approximately normal distribution with no appreciable skewness, thus confirming that ring‐current shifts have the overall effect of skewing the distribution to high field. In helices, NH and CαH have a highly significant tendency to resonate to high field, whereas they resonate to low field in β‐sheets. Side‐chain protons resonate slightly to high field in γ‐sheets. Chemical shift distributions are narrowest for side‐chain protons, and widest for amide protons. When only slowly exchanging amide protons are considered, the high field shift for amide protons in helices is more pronounced, but there is only a small difference in sheets. CαH signals at the N‐terminal end of helices tend to resonate to higher field than those at the C‐terminal end, whereas for NH signals it is the C‐terminal end that resonates to higher field. There is no significant effect of position within the helix on side‐chain signals, implying that the helix dipole has little effect on

ISSN:0006-3525    

DOI:10.1002/bip.360291009

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe peptide Boc‐Val‐Val‐Aib‐Pro‐Val‐Val‐Val‐OMe has been synthesized to investigate the effect of introduction of a strong β‐turn promoting guest segment into an oligopeptide with a tendency to form extended structures.1H‐nmr studies in solution using analysis of NH group solvent accessibility and nuclear Overhauser effects suggest an appreciable solvent dependence of conformations. In chloroform a 310‐helical structure is favored while in dimethylsulfoxide an Aib‐Pro β‐turn with extended arms on either side is suggested. In the crystal, the backbone forms a somewhat distorted 310‐helix despite the presence of a Pro residue in the middle. Among the four possible intrahelical hydrogen bonds three are of the 4 → 1 type and one 5 → 1. Head‐to‐tail NH ⃛OC hydrogen bonds link the helical molecules into continuous columns. The space group is P212121witha=

ISSN:0006-3525    

DOI:10.1002/bip.360291010

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

年代:1990

数据来源: WILEY

摘要:

AbstractTomato bushy stunt virus particles have previously been physically and chemically well characterized. Different strains, however, are known to have different host plants and symptoms, and they can be distinguished serologically. In an attempt to correlate this behaviour with physicochemical properties, we have performed a comparative study on isolates of four of the main variants of this virus (Type strain, petunia asteroid mosaic virus, pelargonium leaf curl virus, and carnation Italian ringspot virus) with regard to sedimentation velocity characteristics, translation diffusivity (from quasi‐elastic light scattering measurements), and molecular weight (from both low‐speed sedimentation equilibrium and the Svedberg equation).It is demonstrated that there are no clear differences between the four strains, particularly insofar as their sedimentation characteristics (both velocity and low‐speed equilibrium). There is some suggestion from diffusion measurements that the Type strain virus particles may have a higher mass, although the presence of some aggregation phenomena may provide an alternative explanation for the diffusion

ISSN:0006-3525    

DOI:10.1002/bip.360291011

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

年代:1990

数据来源: WILEY