摘要:

AbstractThe problem of deducing the DNA structure with correct base pairing and specific symmetry is formulated in the form of algebraic equations. In this way the number of independent variables determining double‐helix conformation can be reduced from six to four. The effectiveness of the method is illustrated by the computations for A‐DNA and B‐DNA. The method allows one to predict all possible conformations of the complementary nucleic

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141102

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe study of Cu(II)–poly(L‐arginine) complexes by potentiometric titration, as well as by optical, circular dichroism, and infrared spectra, provides information about the nature of ligands and the coordination sphere around the metal ion. Three different complexes have been identified. The first, which is formed below pH 8, contains two guanidinium nitrogens and two water molecules at the corners of the coordination square. The constant of the overall process as determined by the Gregor method equals 2.0 ± 0.1 × 10−9. The two other complexes form between pH 8 and 10.5 and they contain two guanidinium and two peptide nitrogens as nearest ligands. One of them is a monomer and the other probably a dimer, which differ in the symmetry of the coordination sphere around the cupric ion. The optical spectra of the three complexes show an absorption band at 260 nm that we have assigned to a charge‐transfer transition between a σ metal nitrogen (amine) molecular orbital and adx2−y2 metal orbital. The spectra of the two complexes containing peptide nitrogens exhibit another absorption band at 320 nm, which we have assigned to a charge transfer from a π orbital of the amide group to thedx2−y

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141103

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

年代:1975

数据来源: WILEY

摘要:

AbstractOligopeptides having the general formulaN‐carbobenzoxy(γ‐methyl‐L‐glutamyl)n‐dimethyl‐L‐glutamate (withn= 1, 3, 5, 7, 11) were prepared, using both solid‐phase synthesis and conventional peptide couplings in solution. The appearance of an ordered structure with increasing chain length was studied in organic solvents and at the air–water interface. The results obtained by thin‐layer chromatography were interpreted. All the studies have demonstrated a very similar behaviour of this type of oligopeptide in soluti

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141104

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

年代:1975

数据来源: WILEY

摘要:

AbstractTwo sequential polypeptides, poly(O‐benzyl‐L‐Tyr‐γ‐benzyl‐L‐Glu‐L‐Ala‐Gly) and poly(ε‐benzyloxycarbonyl‐L‐Lys‐L‐Glu‐L‐Ala), were synthesized, the former by the pentachlorophenyl ester of the tetrapeptide monomer and the latter by the azide of the tripeptide monomer. After deprotection and dialysis, poly(L‐Tyr‐L‐Glu‐L‐Ala‐Gly) was obtained in 71% yield and had a molecular weight of 53,000. The circular dichroism spectra (CD) of the polymer at pH's 7.2, 10.5, and 11.8 and of oligomers and of the monomer at pH 7.2 indicated that the polymer exists in an α‐helical conformation.After deprotection, poly(L‐Lys‐L‐Glu‐L‐Ala) was obtained in 37% yield and had a molecular weight of 3000. The CD spectra of the polymer at pH 7.2 and 2.8, and of the monomer at pH 7.2, indi

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141105

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

年代:1975

数据来源: WILEY

摘要:

AbstractStatistical thermodynamic theories have been developed in order to explore the consequences of two prominent models of length regulation in linear protein aggregates: the length‐determining factor model and the cumulated strain model. In the former, the possibility that the final subunit is bound with extra stability has been incorporated. Calculations explore the dependence of the sharpness of the onset of extensive polymerization, and the breadth, shape, and most probable value of the distribution as functions of concentrations of template and polymerizing subunit, of subunit association constant, of the strain free energy, and of the maximum length and extra stability of the last subunit in the length‐determining factor model. Numerical calculations are made with particular reference to the parameters of bacteriophage T4 tail‐core polymerization. Both models predict suitably narrow length distributions with plausible values of the thermodynamic parameters. The length‐determining factor model may exhibit highly cooperative behaviour, with either fully polymerized or very short aggregates being observed as the productK[C] of association constant and free monomer constant is varied. This cooperativity is accentuated as binding of the final subunit becomes more stable. Species of intermediate length will be observable only if the length‐determining factor is shortened. In the cumulated strain model, ifK[C] is lowered at constant strain free energy per subunit, shorter aggregates will be observed; but increasingK[C] will not yield appreciably longer polymers. As [C] is lowered, the distribution will rema

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141106

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

年代:1975

数据来源: WILEY

摘要:

AbstractRaman spectra are reported for crystalline nonactin, monactin, dinactin, trinactin, and tetranactin and their solutions in CCl4, CHCl3, CH3OH, and 4:1 (v/v) CH3OH:CHCl3. The macrotetrolide nactins selectively bind a wide variety of cations, and are important model compounds for the study of ion complexation. The conformations of nonactin, monactin, and dinactin in solution are similar. Their conformations are found to be sufficiently open to permit the ester carbonyl groups to form hydrogen bonds with CH3OH; this gives rise to characteristic changes in the vibration frequencies associated with the ester groups. Nonactin, which is the least soluble of the nactins in CH3OH, is also the least effective at forming hydrogen bonds with CH3OH. The greater ability of the higher nactins to form hydrogen bonds with CH3OH may be due to the increased inductive effect of ethyl over methyl side chains, which may increase the dipole moment of the ester carbonyl groups. Spectra of crystalline nonactin, monactin, and tetranactin are fairly similar, while the spectra of dinactin and trinactin comprise a second, distinct family. This is consistent with X‐ray crystallographic studies, which show that nonactin and tetranactin form monoclinic crystals, while trinactin is triclini

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141107

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe preparation of the co‐oligopeptides of the series H‐Gly‐Trp‐(Gly)n‐Trp‐Gly‐OH (n= 0, 1, and 2) and of a number of other unprotected co‐oligopeptides of glycine and tryptophan is reported. The syntheses have been carried out by conventional methods, using, in general,N‐hydroxysuccinimide esters for the coupling steps. All the oligopeptides were obtained after purfication as colorless and crystalline products, and gave only one spot on thin‐layer chromatography. Specfic problems connected with the synthesis and purficiation of optically pure tryptophan‐containing p

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141108

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe uv absorption and circular dichroism (CD) properties in water (pH 5.9) and trifluoroethanol of several co‐oligopeptides of glycine and tryptophan have been investigated. These compounds contain one tryptophyl residue, such as H‐Gly‐Trp‐OH, H‐Trp‐Gly‐OH, and H‐Gly‐Trp‐Gly‐OH; or two, such as H‐Trp‐Trp‐OH, H‐Gly‐Trp‐Trp‐OH, H‐Trp‐Trp‐Gly‐OH, and H‐Gly‐Trp‐(Gly)n‐Trp‐Gly‐OH (I,n= 0,1,2). Furthermore, the case of some protected derivatives, such as Z‐Trp‐Gly‐OMe, Z‐Gly‐Trp‐Gly‐OMe, and Z‐Trp‐Trp‐OMe, Z‐Trp‐Trp‐Gly‐OMe, Z‐Gly‐Trp‐Trp‐Ome were investigated. The extinction coefficients in H2O in the region of the L bands, referred to one mole of tryptophyl residue, are essentially the same for all compounds within the limit of experimental error, thus indicating that no strong chromophoric interaction takes place in the oligopeptides containing two aromatic residues. However, in the far uv region, anomalies in the absorption properties cannot be excluded. The investigated compounds show marked differences in their CD properties. Whereas in the case of lower molecular‐weight peptides (e.g., H‐Trp‐Gly‐OH and H‐Gly‐Trp‐OH), these differences can be ascribed, at least in part, to the influence of the charge end groups on the indole chromophore, in the case of the compounds containing two tryptophyl residues, the differences in CD properties are assumed to reflect the different structures and conformations of the oligopeptides. In particular, we observed a negative dichroic band at ∼225 nm in H‐Gly‐Trp‐Trp‐OH and I(n= 0) in water. In trifluoroethanol, this band has a much larger intensity, and it is present also in Z‐Gly‐Trp‐Trp‐OMe, Z‐Trp‐Trp‐Gly‐OMe, and Z‐Trp‐Trp‐OMe. It is argued that such a negative band is characteristic of the sequence ‐CO‐Trp‐Trp‐, and the possibility that it derives from intramolecular chromophoric interaction is discussed. It is also pointed out, particularly in view of the high ellipticity values found in some cas

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141109

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

年代:1975

数据来源: WILEY

摘要:

AbstractAn electron microscopic investigation on the structure of fibrin is reported. Fibrin morphology was investigated in a wide variety of experimental conditions, and by carefully controlled staining procedures. Two main band patterns A (230‐Å‐spaced main dark bands) and B (230‐Å‐spaced main light bands) are observed for stained fibrin; it is shown that the former results from the superimposition of both positive and negative staining, and the latter is given by positive staining. By suitable denaturation experiments, it was found that the fiber is composed of a regular alternation of lose and dense regions along the axis.We have assumed that the monomer of fibrin is described by the three‐nodular model of Hall and Slayter, as supported by recent investigations. The monomers are arrayed according to a head‐to‐tail sequence along the fiber, and to a staggered lateral association. This model accounts for all the experimental observations, and predicts well the high‐resolution band pattern of fibrin. It further agrees with the results of a recent work on the early stages of the fibrinogen‐t

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141110

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe kinetics of the acid hydrolysis ofStreptococcus salivariuslevan were studied by examining the weight‐average molecular weight. The molecular weights were obtained in a continuous manner from light scattering. Two first order reactions were observed: an initial rapid reaction in competition with a slower reaction.Activation energies, activation entropies, as well as the rate dependence upon substrate and hydrogen ion concentrations were determined. The data seem to indicate that the fast reaction is related to the breaking of branch‐point bonds while the slower reaction is related to the breaking of main‐chain bonds. Thus, levan hydrolysis seems to be fundamentally different from the completely random degradation of other branched polysaccharides, i.e., dextran, glycogen, and amylop

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141111

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

年代:1975

数据来源: WILEY