摘要:

AbstractThe template directed synthesis of poly[d(A‐T)] from the nucleoside triphosphates in the presence of DNA polymerase I is carried out continuously in a stirred flow reactor for the first time. The initial objective is to test the kinetic stability of the established steady states at various flow rates. Graphical analysis predicts instable steady states for certain high flow rates. As a consequence of instabilities multiple steady states and steady‐state hysteresis may occur. Steady‐state hysteresis has now been found experimentally. For a different enzyme fraction of low exonuclease activity we found the steady‐state absorbance at 260 nm to be almost invariant with flow rate at high enzyme concentrations even if the flow rate was increased by a large factor. We call this phenomenon kinetic buffering. Relaxation of a large flow perturbation approaches the steady state in a sigmoidal fashion. Concentration oscillations at 260 nm occurred in one experiment using an enzyme fraction of low exonuclease activity after perturbing the steady state by monomer (dATP). Advantages of the stirred flow reactor method over serial transfer are di

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150102

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe positive circular dichroism band observed near 228 nm with poly(L‐proline) responds in a similar fashion to HCl and CaCl2. The spectra in the HCl solutions are compatible with a simple binding equation and a pKnear −2 for the dissociation of a proton from a protonated peptide bond in poly(L‐proline). The data obtained in CaCl2is susceptible to the same analysis, suggesting a pKnear −1.5 for the dissociation of a calcium ion from its complex with poly(L

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150103

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

年代:1976

数据来源: WILEY

摘要:

AbstractA fluctuation theory for electrolyte solutions is developed based on the coupling between the equations of nonequilibrium thermodynamics and the Poisson equation. The resulting fluctuation theory is applied to the analysis of electrophoretic light scattering. It is shown that in a binary electrolyte solution (two ionic species), the Doppler shift is not determined by the electrical mobility of either ion, but depends instead on the rate of change of transference number with salt concentration. In addition the ionic relaxation time is shown to be proportional to the conductivity of the solution.

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150104

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

年代:1976

数据来源: WILEY

摘要:

AbstractExperimental binding isotherms relative to the interactions between proflavine and poly(A) or DNA are analyzed by comparison with theoretical models dealing with competitive cooperative bindings.In the case of poly(A), there are apparently no specific binding sites for the positive co‐operative binding (complex I) leading to dye aggregation along the polyanionic chain. The second complex (complex II) seems to involve specific base‐dye interactions, but it cannot be said whether this binding displays negative cooperativity or noncooperativity. None of the two simpler theoretical models agree quantitatively with all experimental data. A plausible interpretation can be given if it is assumed that (i) the electrostatic binding of one isolated bound dye molecule (nucleus of complex I) involves a definite interaction between a phosphate group and the positive charge of the dye; (ii) the structure of complex II is such that a dye–phosphate ionic interaction is maintained.In the case of DNA, our model of monoexclusive interactions fits the data more closely than does the model of biexclusive interactions. This gives experimental support for structural models in which the intercalated molecule interacts preferentially with one strand of the double helix and blocks only one phosphate for electrostatic binding. In order to propose a mechanism consistent with equilibrium and relaxation kinetic data, a modified reaction scheme is considered which takes account of the cooperativity effects in external binding and extends previous m

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150105

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe far‐ultraviolet circular dichroic spectrum of the 39‐residue peptide hormone porcine corticotropin and the biologically active fragment corticotropin 1–24 is negative from 250 nm to 195 nm in water, but in 6Mguanidinium chloride a positive band appears at about 225 nm. The temperature and guanidinium chloride dependence of this spectral transition indicates the absence of any stable ordered secondary structure in corticotropin and the spectrum is seen to be in only partial agreement with results using the model peptide chromophore, Ala‐Ala‐Ala. Using oligopeptides containing aromatic amino acid residues sandwiched between glycyl residues, it is shown that the shape and intensity of the corticotropin 225 nm positive band which appears in 6Mguanidinium chloride is in agreement with the far‐ultraviolet transitions of the aromatic chromophores in the hormone. Curve resolution of the near‐ultraviolet circular dichroic spectrum of corticotropin and comparison of the rotational strengths of the phenylalanyl and tyrosyl bands reveals no evidence for increased rotational freedom in 6Mguanidinium hydrochloride. Spectral changes are observed, however, in the transitions arising from the single tryptophan. This study suggests that corticotropin in aqueous solution may serve as a better model for the circular dichroic spectrum of the aperiodic regions in globular proteins than either synthetic homopolypeptides or reference proteins for which spectral and X‐ray diffraction dat

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150106

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

年代:1976

数据来源: WILEY

摘要:

AbstractA Malvern laser light‐scattering instrument has been modified for use at scattering angles down to 5° and both total intensity and quasi‐elastic scattering experiments. A sample of sheared, length‐fractionated calf‐thymus DNA was characterized by sedimentation, viscosity and electron microscopy. Quasi‐elastic scattering and absolute intensity determinations were performed with the laser instrument and intensity determinations only with a Fica conventional light‐scattering photometer. The total intensity experiments gaveM̄w= (3.75 ± 0.15) × 106and 〈R2〉1/2z= (206.9 ± 10.3) nm which yielded a value for the persistence length, allowing for polydispersity, of 66 ± 6nm. The quasi‐elastic experiments at scattering angles below 20° gaveD020, w= (2.23 ± 0.06) × 10−8cm2/sec which combined withS020, w= 15.6 in the Svedberg equation gaveM̄w= (3.73 ± 0.18) × 106. In addition, from the higher angle data we extracted a value of the longest intramolecular relaxation time, τ1 of 17.5 msec. This is not in particularly good agreement with τ1 predicted by the Zimm–Rouse theory using our other experimental parameters. The disagreement may be due to the restricted applicability of the Zimm–Rouse spring‐bead model as a quantitative representation of DNA molecules. Alternatively, it may be due to present difficulties in the unambiguous interpretation of molecular motions from the

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150107

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

年代:1976

数据来源: WILEY

摘要:

AbstractWe have measured the binding equilibria of proflavin to T2L bacteriophage, in both “slow” and “fast” sedimenting forms, and to free T2L DNA. Measurements were carried out by difference spectroscopy at 430 nm at temperatures from 13 to 43°C and at pH 5.6 and 7.6. We found no significant difference in the binding parameters of the two phage forms. Also, the fraction of nucleotides available as binding sites for proflavin was the same for both free and intraphage DNA. However, the binding constant is about an order of magnitude lower for encapsulated than for free T2L DNA, due to the decreased exothermicity of the binding reaction within the ph

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150108

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

年代:1976

数据来源: WILEY

摘要:

AbstractUsing the formalism of nearest‐neighbor Ising model and assuming that the allowed states for a monomeric unity of a polypeptide chain in solutions containing strong acids are E (helix), C (coil), and CS (solvent‐bonded coil), the partition function of the system was deduced analytically. Equations were obtained which permitted the prediction of the characteristic thermodynamic behavior of the helix–coil transition under these conditions. These equations were used to examine critically the possible correlations between experimental data obtained using different techniques. Particular attention was devoted to quantities called “transition enthalpies,” obtained from the slope of the transition curves at the point where the helix fraction is one‐half (ΔH optexp), or for measurements of the heat of solution of the polymer over the total range of solvent composition (ΔH solexp), or from heat capacity measurements taken at various temperatures (ΔH calexp). Literature data of ΔH jexp(j = opt, sol, cal) for the system poly‐γ‐benzyl‐L‐glutamate in mixtures of dichloroacetic acid and 1,2‐dich

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150109

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

年代:1976

数据来源: WILEY

摘要:

AbstractAn all‐order classical coupled oscillator theory in which monomer band shapes are explicity taken into account is applied to the calculations of polynucleotide circular dichroism. Calculations are shown for ApA and oligoadenylic acid of varying chain lengths, in both RNA and B‐DNA geometry, and the advantages of this theory are assessed. By introducing an effective dielectric constant, good agreement with measured spectra is obtained. Variations in monomer parameters are tested in an attempt to eliminate remaining discrepancies between calculated and measured spec

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150110

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe fidelity achieved in first derivative profiles of DNA thermal denaturation is shown to depend on a number of factors including the thermal increment of data gathering, the precision of absorbance readings, and the manner in which data are smoothed prior to calculating the derivative of hyperchromicity. The closeness with which thermal denaturation data can be fitted by a cubic polynomial is carefully considered, and a derivation is presented for the estimated error in calculated values of the derivative of hyperchromicity with respect to temperature. After reviewing both theoretical and experimental evidence for the expected minimum width of a thermal transition in DNA, we conclude that thermal increments of 0.05°C or less are required for an adequate representation of transitions in naturally occurring DNA's.Data gathered under conditions meeting the requirements suggested here for quantitative recording of thermal denaturation profiles (Vizard and Ansevin, submitted for publication) show that virtually all of the high‐resolution thermal denaturation profile of a simple, naturally occuring DNA may consist of small subtransitions, which we call thermalites. The finding of substransitions is consistent with current theories of DNA melting. A particularly well‐resolved thermalite of λ bacteriophage DNA has a breadth of only 0.30°C (2σ width), and thus is narrower than previously reported thermal transitions for DNA. For this thermalite, the combination of width, shape, and position in the profile suggests that the substransitions observed in accurately recorded DNA thermal denaturation profiles are not described satisfactorily by existing theories.Knowledge of the requirements for the quantitative recording of thermal denaturation profiles should greatly favor the usefulness of denaturation experiments for physical genomic a

ISSN:0006-3525    

DOI:10.1002/bip.1976.360150111

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

年代:1976

数据来源: WILEY