摘要:

AbstractTheoretical calculations predict that the differential melting curves for random polynucleotide sequences having lengths up to several tens of thousands of base pairs have a clear‐cut fine structure. This structure appears in the form of multiple narrow peaks 0.3–0.4°C wide on the bell shaped main curve. The differential melting curves have different shapes for different specific sequences. The theory also predicts the disappearance of the fine structure when the length of the sequence increases and when circular, covalently closed DNA is considered instead of the open structure. The predictions of the theory were confirmed by the measurements of differential melting curves for open and covalently closed circular forms of DNA for PM2 phage (N= 104base pairs) and also for other phage DNA's of different length: T7 (N= 3.8 × 104);SD(N= 9.2 × 104); T2 (N= 17 × 104). It was shown that the effect of fine structure results mainly from the cooperative melting out of DNA regions 300–500 base p

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150602

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

年代:1976

数据来源: WILEY

摘要:

AbstractA general theory has been developed for conformational intramolecular transitions in a single macromolecule with a high degree of polymerization (an infinite length model) capable of forming two types of ordered structures: the α‐helix and the folded β‐structure, as well as acquiring the random coil conformation. The phase diagram analysis of this system has shown that the regular β‐structure state is separated from all other states of the chain by the phase boundary line. Any intersection of the phase boundary is a phase transition which can be either of the first order or second order, depending on values of the energy parameters of the system. Mechanisms of intramolecular rearrangements: β‐structure–random coil and α‐helix–β‐structure have been discussed. It has been shown that there exist two different mechanisms for each of these rearrangements, and the regions of parameter variation corresponding to each mechanis

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150603

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

年代:1976

数据来源: WILEY

摘要:

AbstractMonte‐Carlo calculations of geometric and thermodynamic characteristics of the α‐helix and the β‐structure of polypeptides have been carried out. To describe a hydrogen bond both the Lippincott–Schroeder and Morse potentials were used. The internal rotation angles φ and ψ in the α‐helix have been shown to fluctuate in the range of ±7°. The distribution functions on angles φ and ψ and on hydrogen bond lengths and angles in the α‐helix have been computed and compared with those in myoglobin and lysozyme. Thermodynamic characteristics of the α‐helix calculated in different approximations with the two forms of the hydrogen bond potentials have also been compared. The data obtained are close to the experimental values for polypeptides in neutral solution.Some geometric and thermodynamic characteristics of the regular parallel and antiparallel and irregular antiparallel β‐structure have been found. In the β‐structure the internal rotation angles vary within the interval ±15–20°. An increase in the cross and longitudinal dimensions of the β‐structure only slightly influence both the geomet

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150604

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

年代:1976

数据来源: WILEY

摘要:

AbstractChlamydocin, Iabu‐L‐Phe‐D‐Pro‐LX, is a naturally occurring cyclic tetrapeptide that exhibits high cytostatic activity. The conformation of the peptide ring, as well as the stereo configuration in the vicinity of the epoxide ring, have been established by a single‐crystal X‐ray study of dihydrochlamydocin: C28H40N4O6·H2O. It crystallizes in the monoclinic space group P21witha= 12.616(6) Å,b= 12.355(6) Å,c= 9.442(5) Å, and β = 99.5(1)°. The structure was solved by the symbolic addition procedure for phase determination followed by the tangent formula method of phase refinement. This structure represents the first cyclic tetrapeptide in which all four peptide units have been found in thetransconformation; however, each peptide unit is significantly nonplanar with ω angles deviating by 14–24° from the ideal value of 180°. This molecule contains two intramolecular 3 → 1 hydrogen bonds and experimentally determined parameters for these seven‐

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150605

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

年代:1976

数据来源: WILEY

摘要:

AbstractMoment index displacement automatically corrects a number of significant nonrandom instrumental errors in fluorescence time‐decay measurements. Three‐component data, obtained by measuring the fluorescence decay of three different species mixed in the same solution, were used as a test sample. It was shown, as predicted by theory, that moment index displacement corrects three nonrandom instrumental errors: (1) the presence of scatter in the data; (2) time origin shifts between lamp and fluorescence data; and (3) lamp drift, or time‐dependent changes in the shape of the excitation curve. The data clearly show that the use of the method of moments with moment index displacement to analyze fluorescence decay data is not a curve‐fitting procedure. This procedure will accurately obtain decay parameters for multiple‐exponential decays from certain badly distorted data, yielding a calculated curve very different from the ac

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150606

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe preparation of the co‐oligopeptides of the series H‐Gly‐Phe‐(Gly)n‐Trp‐Gly‐OH (n= 0, 1, 2) and of other free peptides of glycine,L‐tryptophan, andL‐phenylalanine is reported. The syntheses have been carried out by conventional methods, usingN‐hydroxysuccinimide esters for the coupling steps. The ultraviolet absorption properties of the free peptides have been investigated in water. No hypo‐ or hyperchromicity was found for the aromatic chromophores, with the exception of H‐Gly‐Phe‐Trp‐OH, which shows a small but significant hypochromicity. The contribution of the peptide bond to the molar absorptivity in the far ultraviolet has been separated from that of the side chain plus the COO−group by plotting the measured molar absorptivity ϵ of the farthest accessible uv maximum as a function of the number of peptide bonds (nA). The peptide bond contribution proved to be independent ofnAin the rangenA= 1–5, thus ruling out the onset of helical confor

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150607

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

年代:1976

数据来源: WILEY

摘要:

AbstractFluctuations in backbone dihedral angles in the α‐helical conformation of homopolypeptides are studied based on an assumption that the conformational energy function of a polypeptide consisting ofnamino‐acid residues can be approximated by a 2n‐dimensional parabola around the minimum point in the range of fluctuations. A formula is derived that relates 〈ΔθiΔθj〉, the mean value of the product of deviations of dihedral angles ϕiand ψi(collectively designated by θi) from their energy minimum values, with a matrix inverse to the second derivative matrixF,nof the conformational energy function at the minimum point. A method of calculating the inverse matrixFn−1explicitly is given. The method is applied to calculating 〈ΔθiΔθj〉 for the α‐helices of poly(L‐alanine) and polyglycine. The autocorrelations 〈(Δϕi)2〉 and 〈(Δψi)2〉 at 300°K are found to be about 66 deg2and 49 deg2, respectively, for poly(L‐alanine), and 84 deg2and 116 deg2, respectively, for polyglycine. The length of correlations of fluctuations along the chain is found for bo

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150608

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe water‐soluble poly(1‐vinyl‐2‐ethylimidazole) quaternized with ethyl bromide and lauryl bromide was prepared; lauryl group content, 8.8 mol% (L‐9), 28.9 mol% (L‐29), and 40.9 mol% (L‐41). The λmaxvalue of methyl orange near 460 nm shifted to shorter wavelengths (417–433 nm) in the aqueous solution of L‐29 and L‐41, and the intrinsic viscosity of L‐29 was more than ten times smaller than that of L‐9. The rate and equilibrium constants (kƒandK) for addition of cyanide ion to theN‐substituted 3‐carboxamidopyridinium ions were studied at 30°C, whereN‐substituents employed weren‐propyl,n‐hexyl, benzyl, 2,6‐dichlorobenzyl, andn‐lauryl. The kinetic parameters forn‐lauryl‐3‐carboxamidopyridinium were markedly increased in the presence of L‐29 and L‐41 and with increasing polymer concentrations (84‐fold forkƒand 7800‐fold forK), especially at low ionic strength, whereas L‐9 decelerated the addition reaction. These distinct behaviors mean that L‐29 and L‐41 are classified as micellelike polymers and L‐9 as a polyelectrolytelike polymer. However, L‐29 depressed the rate of the forward reaction for benzyl‐3‐carboxamidopyridinium, acting like a simple polyelectrolyte. Therefore, the polymer micelle can provide both the microenvironments characteristic of polyele

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150609

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

年代:1976

数据来源: WILEY

摘要:

AbstractN‐methylmyristohydroxamic acid (1) bound to polymer micelles of laurylated poly(2‐ and 4‐vinylpyridines) (lauryl group contet: 2VP‐L, 30 mol%; 4VP‐L, 33 mol%) quantitatively reacted withp‐nitrophenyl acetate (NpAc) within a few seconds at 30°C, pH 8.95. Second order rate constantskawere 34,000M−1sec−1for 1–2VP‐L and 11,400M−1sec−1for 1–4VP‐L at μ = 0.5, and they were pronouncedly improved by a decrease in ionic strength (ka= 27,500–80,200M−1sec−1at μ = 0.08). In contrast, poly(N‐ethyl‐4‐vinylpyridinium bromide) hardly affected the nucleophilicity of the hydroxamate ion. Therefore, the enhancement was considered to be associated with some micellar characteristics. Typical saturation phenomena of the reaction rate were observed forp‐nitrophenyl hexanoate (NpOCOPe) and 3‐nitro‐4‐acetoxybenzoic acid (NpAcCOOH). It was suggested that binding of NpOCOPe is caused by the hydrophobic interaction, while that of NpAcCOOH is probably induced by the electrostatic interaction. It is demonstrated that the cationic polymer micelle enormously activates the bound hydroxamate anion, and these complexes would be of much in

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150610

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe relaxation behaviour of the sodium salt of poly (L‐glutamic acid) in the solid state has been examined by means of dynamic mechanical spectroscopy. Bound water was found to exert a profound influence on the relaxation behaviour and on a bulk property, the rigidity. Certain features of the loss spectrum have been identified with the hydration‐dependent β‐to‐α conformational transition. Thus two side‐chain relaxations are observed below ambient temperature, one associated with the β from (β1β) and a second at a lower temperature associated with the α form (β1α). The greater rigidity of the α form below the relaxation temperature and the larger rigidity drop accompanying the β1αcan be explained in terms of the structural differences of t

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150611

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

年代:1976

数据来源: WILEY