摘要:

AbstractThe conformational properties of a series of gastrin‐related peptides in aqueous solution and in 2,2,2‐trifluoroethanol (TFE) have been investigated by CD measurements. In aqueous solution the peptides Leu32‐HG‐34 (human big gastrin), Nle15‐HG‐17 (human little gastrin), and Nle11‐HG‐13 assume a random‐coil structure in the pH range 3–7. In TFE the three hormones fold into partially ordered structures, consisting of mixtures of α‐helix, β‐form and random coil. Comparison with the CD properties of the shorter gastrin peptides HG‐4 (tetragastrin), Nα‐Boc‐HG‐5 (pentagastrin), and HG‐7 (heptagastrin) indicates that the biologically important C‐terminal sequence Trp‐Met‐Asp‐Phe‐NH2in TFE does not maintain the same geometry upon elongation of the chain at the N‐terminus from 4 to 34 residues. Thus, the various conformations in solution of the gastrin peptides examined do not provide a structural explanation for their very similar biological activity. Therefore, we hypothesize that the C‐terminal tetrapeptide amide folds into an “activ

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200402

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

年代:1981

数据来源: WILEY

摘要:

AbstractOligosarcosines with two to seven sarcosine units terminated by an electron donor (p‐dimethylaminoanilide group) and an electron acceptor (3,5‐dinitrobenzoyl group) were synthesized by a liquid‐ or solid‐phase method. The oligomers showed a distinct charge‐transfer (CT) absorption in chloroform and ethanol solutions at low enough concentrations to eliminate the contribution of intermolecular CT interaction. Fractions of the oligomers which form the intrachain CT complex were evaluated at infinite dilution and plotted as a function of the number of sarcosine unitsn. The plot showed an alternating higher and lower tendency with the increase ofnfromn= 3 to 7; the total maximum was found atn= 4. The maximum reached 0.24 in chloroform, which is higher than that expected for an unperturbed oligosarcosine chain free from the end‐to‐end interaction, by an approximate factor of 50. The alternating chain‐length dependence was found to be governed by an alternating tendency in the conformational enthalpy required

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200403

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

年代:1981

数据来源: WILEY

摘要:

AbstractMonte Carlo conformational calculations for oligosarcosines having terminal electron‐donor (D) and ‐acceptor (A) chromophores [A‐(Sar)n‐D,n= 2–8] were carried out. The bulkiness of the terminal chromophores, the conformational energies, and the charge‐transfer (CT) interaction energy were taken into account in the calculation. The equilibrium constant for the intramolecular end‐to‐end CT interaction was evaluated, and the result was compared with the experimental data. The alternating chain‐length dependence of the equilibrium constant observed experimentally was reproduced by the simulation and the solvent dependence of the equilibrium constant was also rea

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200404

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe protein actinoxanthin (molecular weight 10,300) crystallizes in space groupP212121, with cell dimensionsa= 30.9 Å,b= 48.8 Å,c= 64.1 Å, andz= 4. The three‐dimensional structure of actinoxanthin at 4‐Å resolution was determined by x‐ray methods on the basis of experimental data from the native protein and five isomorphous derivatives. At the stage of solving the phase problem, the heavy atoms in the derivatives were located using direct methods. The actinoxanthin molecule can be described as an oblate ellipsoid with approximate dimensions 20 × 30 × 40 Å and consists of two different sizes of folded units separated by a well‐defined cleft. The larger unit, including the N‐ and C‐terminals of the protein chain, is characterized by a significant content of β‐sheet structure. The smaller unit, containing two deca‐ and hexapeptide cycles closed by disulfide bonds, has a mai

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200405

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

年代:1981

数据来源: WILEY

摘要:

AbstractThis article reports on both (1) the precision and capability of a computerized multidimensional spectrophotometric system recently developed in our laboratory and (2) the high‐resolution study of the helix–coil transition of poly(L‐glutamic acid)[poly(Glu)], especially with regard to the discovery of an overlooked transition which is attributable to order–disorder rearrangement of the poly(Glu) side chain in the α‐helical conformation. This study was made possible by the high performance of the system used. The simultaneous and continuous measurement of the circular dichroism, the absorbance and light‐scattering intensity, and the pH titration curve of poly(Glu) in aqueous salt solution was carried out under continuous scanning of pH ranging from 8 to 2. Besides the well‐known random coil to α‐helix transition that occurs at about pH 5.5, a highly cooperative transition, which is indicated as a small but definite step in several spectral dimensions, is observed for the first time at pH 4.3. The transition is ascribed to an order–disorder conversion of the side chain on t

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200406

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

年代:1981

数据来源: WILEY

摘要:

AbstractObservations of induced circular dichroism (CD) bands in chloroform solution demonstrate the formation of specific, asymmetric complexes of the aromatic ligands 2‐pyridone and 2,6‐dichlorobenzoic acid with cyclic dipeptides of the general formulacyclo(L‐Pro‐X). The induced CD changes sign with the configuration ofXdue to subtle influences of the side chain on the geometry of the complex. Computations of interaction energies suggest that a plausible model for the complex of an aromatic ligand with the ‐CONH‐ of thecissecondary amide is a nearly planar arrangement of six heavy atoms in a ring containing two hydrogen bonds. The observed CD is matched by that computed for a tilt of the aromatic ligand toward the side chain ofX. Binding constants were determined from the induced CD as a function of ligand concentration. For dichlorobenzoic acid these are about 450m−1for the secondary amide and 50m−1for the tertiary amide. For pyridone the binding constant is about 45m−1for either the secondary or tertiary amide. For comparison self‐dimerization constants determined by vapor‐pressure osmometry in chloroform solution at 25°C are 870, 350, 50, and 20m−1for pyridone, benzoic acid, dichlorobenzoic acid, andcyclo(

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200407

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe shape and structure of nucleosomes from chicken erythrocytes as a function of ionic strength in solution using the complementary techniques of streaming birefringence and intrinsic viscosity were studied. As characterized by both rotational diffusion and optical anisotropy, three distinct conformational levels were observed. Above ∼8 mMionic strength, the particles are oblate ellipsoids or discs with axial ratio of ∼0.5. Below ∼8 mM, two structural variants were observed: a relatively more symmetrical particle which exists between ∼8 and ∼0.5 mM, and a relatively asymmetric structure below ∼0.5 mM. Birefringence data are consistent with an “opened clamshell” type of model for the first of these and with a somewhat compacted form of linear DNA for the latter. The results provide insights into possible conformational states of transcriptionally active chromatin at the nucleosomal lev

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200408

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

年代:1981

数据来源: WILEY

摘要:

AbstractA Monte Carlo method is presented to calculate equilibria for the binding of ligands to one‐dimensional heteropolymers. Equivalency with other methods suitable for particular cases was verified (i.e., matrix and combinatorial methods). The principal interest of this Monte Carlo method is in its facility for adaptation to any physically conceivable binding model and that it gives access to the parameters accounting for partial binding to each different type of site. General properties of binding isotherms with excluded‐site effects and relations between partial binding ratios and partial free site ratios are discussed. An effective calculation is presented for illustration of the met

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200409

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe interaction of tilorone with DNA and five synthetic polydeoxyribonucleotides [(I): poly[d(A‐T)]·poly[d(A‐T)]; (II): poly[d(A‐C)]·poly[d(G‐T)]; (III): poly[d(G‐C)]·poly[d(G‐C)]; (IV): poly(dG)·poly(dC); and (V): poly(dA)·poly(dT)] has been investigated. Binding isotherms for the homopolymers were obtained by microdialysis equilibria using14C‐labeled tilorone and interpreted with different models: exclusion effect, associated or not associated with cooperativity, or variable exclusion. Affinity appears to be related more to local structure than to base composition and decreases in the following order: (I)>(II)>(III)>(IV)>(V). Intercalation in circular DNA was demonstrated by electrophoresis migration and electron microscopy, which yielded an average unwinding angle of 7° per bound dye. The behavior observed in CD and UV spectroscopy shows a sequence similar to the affinities. Tilorone seems to be less intercalated in (IV) and not at all in (V). The experimental binding isotherm of tilorone to DNA was well fitted on the basis of a model where DNA acts as a heterogeneous lattice built with the six different possible couples of adjacent base pairs, each potential site behaving as if it were in the corresponding homopolymer. The results are discussed in terms of specificity of alternating Pyr‐Pur sequences and related to theoretical calculations on intercal

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200410

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

年代:1981

数据来源: WILEY

摘要:

AbstractReceptors are functional membrane proteins on the cell surface that recognize external signals and trigger biological responses by generating intracellular signals. Due to prolonged exposure to external signals, receptors are often desensitized and no longer produce intracellular signals. This simple control mechanism may work without negative‐feedback regulation from another molecule if the active state of a receptor reflects a transient metastable molecular structure. A theoretical framework is developed to identify a metastable state associated with a conformational transition of protein molecules, in which a transient state can be observed somewhat above the equilibrium transition point. The conducting state of the acetylcholine receptor may thus represent a metastable state associated with a conformational transition from the resting state to the desensitized state. Similarly, the conducting state of the voltage‐sensitive sodium channel may represent a metastable state associated with a conformational transition from the resting state to the refractory state. The rates of appearance and disappearance of the transient state, as well as the equilibrium ratio of the two preexisting states, can be estimated from the free energy of protein structure. The appearance of the transient state is generally a multirelaxation process and may show a time lag, while the disappearance is a slower single‐relaxation pr

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200411

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

年代:1981

数据来源: WILEY