摘要:

AbstractWe have studied the effects of temperature, EDTA, and ionic strength on C‐polysaccharides in solution by examining the details of the time‐correlation function using a 96‐channel single‐clipped photon correlation spectrometer. Our linewidth results have shown that the C‐polysaccharides in buffer solution form aggregates of very broad distributions. Thus, fractionation by gel‐filtration chromatography is only mildly effective. Although the aggregate sizes seem to remain relatively constant from 4 to 25°C, a fraction of those aggregates break up to form smaller fragments or monomers at higher temperatures. However, the dissolution‐association process is quite slow and takes days even at room temperatures before the equilibrium is reached. We have also shown that by adding an excess amoutn of EDTA, the aggregates can be broken up. Again the dramatic changes occur only at short delay times suggesting that a protion of the larger aggregates remains. Finally, the amount and size of aggregates depend upon the ionic strength which exhibit a maximumΓT/sin2(θ/2) around 0.1–0.2MKCl.If the activities of polysaccharides in solution depend upon molecular size, the standard techniques such as gel‐permeation chromatography and ultracentrifugation cannot properly characterize the detailed size distribution. Quasielastic laser light scattering can provide us with a qualitative model. The quantitative details must necessarily await more extensive investigations using a combination of the techniques and better fractionation procedures in an appropr

ISSN:0006-3525    

DOI:10.1002/bip.1977.360160502

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

年代:1977

数据来源: WILEY

摘要:

AbstractWe have investigated the B to A conformation change of DNA double helices by a new method “soft‐mode analysis.” We find theoretically that a mode does soften when the vibration normal modes are perturbed by increasing the electrostatic interaction between the unbalanced charges on atoms in the double helix. The same mode also softens for enhanced van der Waals interactions. The mode softening indicates the onset of conformation change. The enhancing of the electrostatic and van der Waals interaction mimic the effect of decreasing the polar nature of the solvent or water of hydration associated with the B conformation DNA. We discuss qualitatively the concept of soft modes and their relation to conformation change as well as their applicability to macromolecules. We discuss previous work in which the normal vibrational modes have been calculated. We also discuss the displacement which comes from the soft mode and show that it correlates very well with that expected for the B to A conformation c

ISSN:0006-3525    

DOI:10.1002/bip.1977.360160503

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

年代:1977

数据来源: WILEY

摘要:

AbstractSpectrophotometric titrations of slightly substituted carboxymethylamylose (CM‐Amy) and diethylaminoethylamylose (DEAE‐Amy) with iodine in the presence of iodide (I2/I−) were carried out as a function of iodide concentration, temperature, and polymeric charge. Binding isotherms for the polymer‐I2/I−complex are reported in terms of an apparent binding constant (Ka) plotted versus degree of saturation of the complex (θ). The dependence ofKaupon polymeric charge is interpreted as evidence for the negatively charged character of the bound species. The cooperative nature of the binding process is evident in the positive slope ofKavs(θ). Whereas the apparent binding constants and binding cooperativities for the derivatives are smaller than for the amylose‐I2/I−complex, the binding enthalpies deduced from the temperature dependence ofKaat θ = 0.5 appear to be the same for amylose and CM‐Amy. A viscometric titration of fully charged CM‐Amy with I2/I−, conducted at dialysis equilibrium between the CM‐Amy‐I2/I−solution and the polymer‐free solvent phase, disclosed a maximum in the plot of intrinsic viscosity ([η])vsθ. The increase in [η] at small θ was interpreted as a reflection of polyelectrolyte expansion provoked by absorption of the negatively charged bound species; the subsequent decline in [η]is attributed to stabilization by I2/I−of compact helical sequences or to the formation at

ISSN:0006-3525    

DOI:10.1002/bip.1977.360160504

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

年代:1977

数据来源: WILEY

摘要:

AbstractWe measured electrically induced changes of some optical properties of DNA solutions. These were the absorption coefficient and the reduced dichroism. The electric fields were applied in the form of 50–300‐μsec‐long pulses of varying field strength, up to 20 kV/cm. Changes of the optical properties were studied during the pulse. Solutions of varying DNA and salt concentrations were used. The qualitative predictions expected from the theory of electrically induced partial denaturation of the DNA were all observed. These are: (1) a decrease of the reduced dichroism at high fields; (2) a concurrent increase in the absorption coefficient; (3) a critical field above which effect (1) and (2) begin to occur; (4) a decrease of the magnitude of the above effects with increasing salt concentration; (5) a return to thestatus quo anteafter short

ISSN:0006-3525    

DOI:10.1002/bip.1977.360160505

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

年代:1977

数据来源: WILEY

摘要:

AbstractAn electron microscope study of collagen fibrils from fixed tail tendons of rats has revealed that from some time shortly after birth until maturity, the fibril diameters have a bimodal distribution. The “two” types of fibril are indistinguishable in both transverse and longitudinal section. Unfixed specimens of eight‐week‐old‐tail tendon showed a similar bimodal distribution of diameters though the positions of the peak values compared to fixed specimens of an eight‐week‐old‐tail tendon were shifted upwards by about 30%. It has also been shown quantitatively that the polar collagen fibrils are directed randomly “up” and “down” with respect to their neighbors. Whilst it has been suggested by others that anastomosis is a feature of collagen structure, the results presented here do not support this hypothesis. Fibrillar units ∼ 140 Å in diameter have been observed and the possibilities that these are elastic fibers or the breakdown products of collagen fi

ISSN:0006-3525    

DOI:10.1002/bip.1977.360160506

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe coupling ofN‐acyl‐α‐amino‐acids with α‐hydroxyacid‐methyl amides results in depsipeptide molecules containing two chiral centers and one ester function inserted between two amide functions. Their conformational features have been investigated by IR spectroscopy, proton magnetic resonance, X‐ray diffraction, and theoretical P.C.I.L.O. calculations.It is shown that most of these molecules are folded by an intramolecular 4 → 1 hydrogen bonding. Two folded conformations, similar to the well known β turn in peptides, are described, the stability of which depends on the configurational sequence in the investigated molecule.LLandLDspecies are folded in two different ways whereas LG sequences containing an achiral hydroxy‐acid residue accommodate both of them. The presence of a N‐terminal achiral amino acid noticeably decreases the folding ratio.The above conclusions are then compared with the conformational features of homologou

ISSN:0006-3525    

DOI:10.1002/bip.1977.360160507

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe effect of various salts on the enzymatic activity of beef‐liver glutamate dehydrogenase, on the binary enzyme‐reduced coenzyme (NADH or NADPH) comples, as well as on the ternary complex with glutamate was investigated in aqueous solution (0.067Mphosphate buffer, pH 7.6). Binding studies in the analytical ultracentrifuge and circular dichroism measurements indicated dissociation of the coenzyme from the enzyme‐coenzyme complex by the action of various salts. The efficiency of this change was largely dependent on the type of anion present and generally followed the series: acetate

ISSN:0006-3525    

DOI:10.1002/bip.1977.360160508

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe semiautomated sucrose gradient system of Lange and Liberman (1974) (Anal. Biochem.59, 129–145) has been used to determine an accurate value of the exponentkof the Burgi and Hershey equation (1963) (Biophys. J.3, 309–321) under conditions of 1Msalt. A complete analysis of the variance ofkwas done for data from both systems. The results lead to the conclusion that the valuek= 0.401 (±0.012 for reproducibility; ±0.019 for total error) obtained here is considerably more accurate than that of Burgi and Hershey (even when corrected for DNA concentration effects and the improved size estimates of T4DNA size). The use of the Burgi and Hershey relationship and a T4DNA metric to determine molecular weights of mammalian DNA requires the utmost precision in the exponent if useful estimates are to be obtained. This also has implications for double‐strand breakage and repair es

ISSN:0006-3525    

DOI:10.1002/bip.1977.360160509

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe addition of a lytic layer to a preformed linear sucrose gradient induces a temporary (up to half a day) initial gradient of considerable steepness which retards the sedimentation of large (>T4) DNAs. Centrifugation at sufficiently slow angular velocities permits the temporary initial gradient to disappear and therefore the sedimentation distance increases, yielding a rotor speed dependent effect on sedimentation distance. Gradients which are free of this effect are described and shown to permit mouse leukemia cell DNA to sediment independently of rotor speed (5–30 krpm

ISSN:0006-3525    

DOI:10.1002/bip.1977.360160510

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe necessary conditions for a unique solution of the sedimentationvsDNA molecular weight equations are considered and applied to the native DNA of the L5178Y mouse leukemia cell. A brief review and critique of the literature of sedimentation anomalies is given to demonstrate that such anomalies are not present in the data reported here. It is shown that the chromosomal DNA of L5178Y cells comes in uniform packages of 1.0 (0.5–2.0) × 1010daltons. All pieces are of an identical size which corresponds to the DNA content of about 1/13 the average chromatid. Both the size estimate and the number of such molecules/cell are confirmed by viscoelastometry. This DNA is shown to be free of radioactively demonstrable protein and/or lipid contaminants and of the same isopycnic density as T4DNA. Variance analysis is applied to determine the precision of all measurements and to pinpoint major sources of error. A relationship between [η] andMis derived for native DNA in 1.0MNaCl. A necessary conclusion from these data is that mammalian chromosome models requiring degrees of polynemy greater than 16‐neme (in G1) are incorrect (to the extent that the L5178Y cell is typical of mammalian c

ISSN:0006-3525    

DOI:10.1002/bip.1977.360160511

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

年代:1977

数据来源: WILEY