摘要:

AbstractThree approaches to the simultaneous sedimentation and diffusion of hands or zones of noninteracting homogeneous macromolecules are examined: (1) The authors' method of moments: (2) the transport me of Sehumaker and Rosenbloom; and (3) the stochastic solution of the Lamm equation due to Gehatia and Katehalski. All three methods indicate that the motion of the maximum of the hand may be used to evaluate the sedimentation coefficient. The moment, method provides relations which appear to be useful for measuring diffusion coefficients. Relations are given for the analysis of resolved components. The problem of measuring sedimentation coefficients of macromolecules with concentration‐dependent sedimentation coefficients is examined. Methods are described for evaluating the sedimentation coefficient in these systems and for obtaining the sedimentation coefficient at infinite dilution. Methods are described for determining the weight‐average sedimentation coefficient in Multi‐component systems, and the differential and integral distribution of sedimentation coefficients of macromolecules with low‐diffusion coeff

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040202

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe conditions for convection‐free hand sedimentation are analyzed in terms of the negative density gradients associated with the leading edge of a band and the positive density gradients generated during the experiment. The amount of material necessary to perform a band‐centrifugation experiment depends on the diffusion coefficient of the macromolecules, which determines the rate at which the concentration at band maximum decreases, and on the extinction coefficient at the wavelength of observation. The maximum negative gradients in bands of macromolecules with diffusion and extinction coefficients typical of proteins, nucleic acids, and viruses are calculated. Positive density gradients generated by diffusion of small molecules between the thin lamella and the bulk solution are calculated for bulk solutions such us 1MNaCl or 95% D2O. These “diffusion gradients” are generally adequate to stabilize bands of the above macromolecules. Positive density gradients generated by sedimentation of salts within the bulk solution may be significant in providing stability near the bottom of the cell. The effects of inadequate stabilizing gradients are discussed, and are found to cause forward spreading of t

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040203

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe kinetics of renaturation of heat‐ or formamide‐denatured DNA have been studied by following the change of optical density at a constant temperature. Solvents of different ionic strength and various DNA samples have been used. At the lower ionic strengths studied, the reaction follows second‐order kinetics, substantiating the hypothesis that strands of native DNA separate upon denaturation and recombine during renaturation. As the ionic strength is increased at a constant temperature, the reaction deviates from simple second‐order behavior. This appears to be the result of the inhibition to rewinding caused by short helical segments in the denatured DNA which are more stable at the higher ionic

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040204

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe structure of renatured T4 DNA has been studied by CsCl density‐gradient centrifugation. It has been found that the products of the reaction differ, depending on the method used for denaturation of the DNA. If denaturation is carried out without taking precautions to prevent chain degradation, for example, by heat, the DNA formed by renaturation shows approximately 70% recovery of the native structure as judged by its density. With long times of annealing, the DNA can recover the native density. This behavior is also observed with bacterial DNA samples. On the other hand, if precautions arc taken to prevent chain degradation during denaturation, two products appear as a result of renaturation. One of them is undistinguishable from native T4 DNA, whereas the second one consists of highly aggregated DNA which shows only a partial recovery of the native structure. With long times of annealing, this second species recovers the native density but retains its highly aggregated nature. At higher ionic‐strengths, renaturation follows a different pattern and a single product is formed. The relevance of all these observations to the kinetic anomalies reported in the previous communication is discus

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040205

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

年代:1966

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040206

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe axial ratios (a/b) of native and 60 min. ultraviolet‐irradiated myosin A molecules were calculated from previously reported sedimentation and diffusion data; values found werea/b= 74,a= 1880 A., andb= 26 A. for native myosin A;a/b= 104,a= 3280 A., andb= 32 A. for 60 min. ultraviolet‐irradiated myosin A. Electrophoretic mobilities gave identical values of 3.2 (±0.1) × 10−5cm.2/v.‐sec. for both native and 60 min. ultraviolet‐irradiated myosin A. From the prior sedimentation and diffusion data, together with newly obtained electrophoretic data, the net chargeZand the charge density σ of native and ultraviolet‐irradiated myosin A molecules were calculated from Henry's equation. The following results were obtained: for native myosin A,Z= 160 negative charges per molecule and σ = 22 coulombs/cm.2; for ultraviolet‐irradiated myosin A,Z= 312 negative charges per molecule and σ = 20 coulombs/cm.2. The results of this study provide an experimental demonstration that, the electrophoretic mobility of charged solute particles is dependent upon the particle charge density and not on the absolute char

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040207

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

年代:1966

数据来源: WILEY

摘要:

AbstractCrystalline proteins, nucleic acids, nucleotides, and nucleosides have been examined by differential thermal analysis. Characteristic thermograms are illustrated for globular, serum, and blood plasma proteins, calf thymus DNA, sodium triticonucleate, sodium thymonucleate, sperm DNA, yeast RNA, adenosine‐3′‐phosphate, adenosine‐5′‐phosphate, disodium adenosine triphosphate, adenosine, and deoxyadenosine. A pronounced effect of moisture on the differential thermal properties of DNA has been observed. It is suggested that solid‐state denaturation is one of the prominent thermal effects recorded by the differential thermal analysis of proteins and

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040208

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

年代:1966

数据来源: WILEY

摘要:

AbstractOptical rotatory dispersion measurements were made on the oligonucleotides (pA)2, (pA)4, and (pA)6at neutral pH over the temperature range 5–85°C., and compared to similar data for polyriboadenylic acid. The data were interpreted in terms of a temperature‐dependent stacking of the bases in the single‐strand oligomers, with very little dependence of the degree of stacking on the chain length. These results can be explained by a theory of cooperative stacking. The degrees of freedom available per residue are rotations about the five backbone covalent bonds and the bond connecting the base to the ribose ring. To nucleate a stacking interaction between neighboring bases the backbone sequence must be ordered as must be the two bases. For this stack to grow by one base a backbone sequence must again be ordered, but only one additional base must be ordered. Thus, the degree of freedom of the base with respect to the ribose ring determines the extent of the cooperative effect and hence the effect of chain length. A matrix formulation of the partition function is presented which incorporates this cooperative nature of the interaction and is shown to be in fair agreement with the data. The entropy of ordering a base with respect to the ribose ring is found to be 0.68 e.u., which suggests that the purine has a torsional oscillation when unstacked, but does not have several isoenergetic positions of internal rotation available. The enthalpy of stacking is found to be −6.5 kcal./mole. A model involving neighbor and next‐nearest neighbor interactions could also account for the data. For all practical purposes, the stacking interactions of successive residues can be treated as independent, i.e., the state of one residue is essentially independent of the state of stacking of its

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040209

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

年代:1966

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040210

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

年代:1966

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040211

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

年代:1966

数据来源: WILEY