摘要:

AbstractA model is developed to explain the following experimental observations: oligomers of the alternating DNA copolymer dAT serve as templates for the enzymatic synthesis of macromolecular dAT; the rate of polymer synthesis with a template oligomer of given length increases to a maximum and then decreases as the temperature increases; the temperature for the maximum rate of synthesis increases with the length of the template. These observations were interpreted in terms of the repeated “slipping” of the oligomer along the product strand to expose template sites. This communication extends this idea. We suppose that the rate‐limiting step in the polymerization is either the attachment of the substrate to the exposed template site or the synthesis of the phosphodiester bond. Then the rate of synthesis is proportional to the equilibrium concentration either of exposed template sites or of template sites occupied by substrate molecules. These concentrations are evaluated in terms of a simple theory of the helix–coil transition. The model qualitatively reproduces the dependence of the rate of synthesis on template length and temperature and predicts rates of synthesis in approximate agreement with exp

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060302

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe sedimentation coefficients of branched and cyclic replicating DNA structures have been calculated taking into account both chain stiffness and excluded volume effects. For branched DNA, the calculated ratioS0(α)/S0(0) of the sedimentation coefficient at degree of replication α to that at α = 0 increases from 1.000 to 1.331 as α goes from 0 to 1. For cyclic replicating DNA,S0(1)/S0(0) = 1.517. The considerable difference between these two ratios for α = 1 suggests that the two types of replicating structures may feasibly be distinguished by sedimentation velocity studies, A similar calculation has been made of the sedimentation coefficient of singly cross‐linked DNA under denaturing conditions, as a function of placement of the crosslink. In 0.195MNa+, the ratioS0(α)/S0(0) varies from 1.000 at α = 0 to 1.124 at α = 0.5, where α is the fractional distance of the crosslink from the end of

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060303

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

年代:1968

数据来源: WILEY

摘要:

AbstractStudies have been made of the d.c. semiconductive behavior of fibers and solid gels of DNA. The semiconductive behavior under high vacuum is similar in solid gels of DNA and stretched fibers of DNA measured along and across the fiber axis. Photoelectric effects have been studied, and an action spectrum is reported which agrees with the absorption spectrum of DNA. No photoelectric effects are observed at wavelengths corresponding to the thermal energy gap. The temperature dependence of the photocurrent has been determined, and the effects of air, oxygen, and nitrogen at different pressures on the photocurrent have been measured.

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060304

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe predominant role of van der Waal interactions in determining the helical conformations of a simple synthetic linear polymer, as well as helical polypeptides, was pointed out in systematic studies by Liquori et al.1,2. In the case of homopolypeptides the conformational analysis carried out on the basis of a simple semiempirical function describing the van der Waal pairwise interactions between the non directly bonded atoms lead to the conclusion that only five helices are allowed (Rα, β, γ, δ,Lα).2,3In view of the close similarities with poly‐L‐alanine, we have investigated by x‐ray and conformational analysis the molecular conformation of poly(S‐lactic acid) which has recently been described by Kleine and Kleine4and Schuls and Schwaab5and studied in solution by Goodman and D'Alagni.6In fact, this polymer may be related to the polypeptide by the interchange of a peptide bond with ester bond along the main chain. This operation is expected to involve only a relatively small change in the steric interaction within the possible helical conformation, but obviously rules out any possibility of hydr

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060305

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

年代:1968

数据来源: WILEY

摘要:

AbstractPoly‐L‐prolines I and II were differentiated by the characteristic bands in the far infrared region. Form I showed two broad bands at about 280 and 160 cm−1and form II two bands at, 400 and 670 cm.−1. Furthermore, three broad bands at about 250, 200, and 100 cm.−1were observed in the spectrum for form II. Infrared absorption bands of the pentamer, hexamer, and octamer oftert‐amyloxycarbonyl‐L‐proline were almost similar to those of poly‐L‐proline II in the 1800–75 cm.−1region. In the far‐infrared region, especially, the absorption bands of these three oligopeptides were in good agreement with that of poly–L–proline II. Accordingly we concluded that the molecules of pentamer, hexamer, and octamer had a helical structure of a left‐handed threefold screw axis. The tetrapeptide oftert‐amyloxycarbonyl‐L‐proline might also have a left‐handed helix, probably one turn, since the tetramer clearly showed an absorption band at about 400 cm

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060306

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe results of the measurement of the far‐ultraviolet absorption spectra ofL‐proline oligomers in water and acetonitrile are summarized as follows. The monomer has an absorption maximum at 182.5 mμ in acetonitrile. The absorption maximum of the dimer is found at 185 mμ and a shoulder appears around 200 mμ, that is, splitting of the absorption spectrum is observed in the dimer. As the degree of polymerization increases, the position of the shoulder shifts toward the wavelength of the absorption maximum of poly‐L‐proline II, with an accompanying increase in intensity. We may describe the absorption peak around 203 mμ of poly‐L‐proline II as identical with the shoulder with an increased intensity. By measurements of optical rotatory dispersion and circular dichroic spectra, it was also confirmed that the appearance of the helical conformation commences at the tetramer. When the number of residues is five or greater, the conformation of the helical structure of poly‐L‐proline II se

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060307

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe conformational properties of poly‐L‐alanine have been examined in aqueous solutions in order to investigate the influence of hydrophobic interactions on the helix–random coil transition. Since water is a poor solvent for poly‐L‐alanine, water‐soluble copolymers of the type (D,L‐lysine)m–(Lalanine)n‐(D,L‐lysine)m, having 10, 160, 450, and 1000 alanyl residues, respectively, in the central block, were synthezised. The optical rotatory dispersion of the samples was investigated in the range 190–500 mμ, and the rotation at 231 mμ was related to the α‐helix content, θH, of the alanine section. In salt‐free solutions, at neutral pH, the three large polymers show high θHvalues, which are greatly reduced when the temperature is increased from 5 to 80°C. No helicity was observed for the small (n= 10) polymer. By applying the Lifson‐Roig theory, the following parameters were obtained for the transition of a residue from a coil to a helical state: ν = 0.012; ΔH= −190 ± 40 cal./mole; ΔS= −0.55 ± 0.12 e.u. Since ΔHand ΔSdiffer from the values expected for a process involving only the formation of a hydrogen bond, and in a manner predicted by theories for the influence of hydrophobic bonding on helix stability, it is concluded that a hydrophobic interaction is also involved. In the presence of salt (0.2MNaCl), or when the ε‐amino groups of the lysyl residues are not protonated (pH = 12), the helical form of the two large polymers (n= 450 andn= 1000) is more stable than in water. Since the electrostatic repulsion between the lysine end blocks is greatly reduced under these conditions, the alanine helical sections fold back on themselves, and this conformation is stabilized by interchain hydrophobia bonds. This structure was predicted by the theory for the equilibrium between such interacting helice

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060308

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe kinetics of a model for the primer‐dependent, polynucleotide phosphorylase‐catalyzed synthesis of oligo‐ and polynucleotides is developed. Numerical solutions are presented which correspond to a wide variety of possible reaction conditions. The model seems capable of explaining the types of behavior which have been experimentally observed for polynucleotide phosphorylase reactions. The most unusual of these is the presence of a transient intermediate of high molecular weight polynucleotide chains which is subsequently degraded to an equilibrium mixture of short oligonucleotides. Methods of estimating the time of occurrence and maximum size of the polymer are discussed. Analytical solutions are developed for the concentrations of free enzyme and unreacted nucleoside diphosphate. In conjunction with equilibrium data these may permit the rate constants required by the model to be deter

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060309

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

年代:1968

数据来源: WILEY

摘要:

AbstractMethods for calculating the rate of cooperative transitions on a linear lattice, for which the helix–coil transition of polypeptides is an example, are reported. The problem is to determine the kinetic characteristics of the transition given the rate constants for a set of elementary steps: in this case, the transformations of individual segments between the helix and coil states. The most straightforward method is to store the state of a long lattice (in which helix and coil segments are represented by 1′s and 0′s) in a computer and to use random‐number techniques to generate its behavior as a function of time. This is, in principle, a solution to the problem, but it requires very large amounts of computer time. We have devised a matrix iteration procedure which allows much faster computation while reproducing the results of the random‐number method accurately. In this procedure the computer operates repeatedly with a transition probability matrix on a vector which represents the time‐dependent state of a finite group of units. The choice of a finite group neglects kinetic correlations between the state changes of units inside and outside the group, but comparison with the random‐number method indicates that these correlations are not important. Thus it is possible to generate the kinetic behavior of the model under essentially any conditions, for either relaxation or large perturbations. Examination of these calculated curves suggests a simple and quite generally applicable solution to the inverse problem—that of evaluating the rate constants from kinetic curves. The initial slope is well defined in almost every case, and since an analytic equation can be written relating this to the rate constants, these can be obtained directly from the initial rate. This latter is therefore the most convenient single measure of

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060310

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

年代:1968

数据来源: WILEY

摘要:

AbstractInfrared spectra of polyglycines I and II obtained at −170°C. have been compared with those obtained at room temperature. The changes in frequency of some of the C—H stretching bands are consistent with the earlier suggestion that C—H …︁ OC hydrogen bonds are present in the structure of po

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060311

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

年代:1968

数据来源: WILEY