摘要:

AbstractA general approach to the determination of relative stability of any pair of con‐formational states of biological macromolecules or their complexes (in particular, to the determination of relative stability of native and disordered states of the macromolecule) has been suggested. For determining the free energy difference of the two states under the conditions when one of them is considerably more advantageous than the other, it is necessary for the macromolecule to be influenced by the transforming agent which levels free energies of both the conformational states, and to determine the external parameter derivative of the free energy difference in the region of the conformational transition induced by the change in this parameter. If the character of the dependence of this derivative on the external parameter (temperature, solvent composition, etc.) is known, then this allows the determination of the free energy difference of the two states under the conditions considered, even including conditions far from the transition region. The value of the derivative of the free energy difference in the transition region in many cases can be measured directly (in particular, when using calorimetry), while in cases when a direct measurement of the derivative is impossible, it can often he estimated experimentally from the steepness of the conformational transition. The methods of this estimation and also a possible character of the change of the considered derivative during variation of the external parameter are considered for the case when the transforming agent is one of the components of the solvent and, consequently, the derivative of the free energy difference is equal to the difference of number of molecules of this component hound with the macromolecule in two conformational state

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070402

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

年代:1969

数据来源: WILEY

摘要:

AbstractBy use of D2O we found that the shortening of the longitudinal proton relaxation time which occurs in the investigated aqueous yeast DNA solutions (≦ 2.4% with 2% protein) was not based on a hydration effect, but was caused by magnetic impurities only. An estimate shows that the mobility of the hydrated water molecules is reduced by less than two orders of magnitude in comparison with the free water molecule

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070403

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe interaction between ionizable carboxyl groups and the conformation of poly‐(glutamic acid) (PGA) in aqueous solution were investigated by the mechanical method. The dynamic rigidity of the PGA solution has a maximum value at the pH corresponding to about 50% neutralization point. This may be due to establishing of a maximum attractive force by proton/charge fluctuation between ionizable carboxyl groups at that pH. The dynamic viscosity has a sharp change in the region of pH 5.5–6.5. It is suggested that this behavior is due to the helix–coil trans

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070404

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

年代:1969

数据来源: WILEY

摘要:

AbstractWool–water systems, at water contents above a threshold value of 22.7 g of water per 100 g of wool keratin, yielded curves of specific heat against temperature showing peaks that are ascribed to the fusion of the absorbed water. Integral and incremental heats of fusion were obtained. Integral heats increase as the square of the water content above the threshold, and incremental heats follow a linear relationship. The incremental heat reaches a value of 55 cal/absorbed water, at the saturation water content, at 0°C of 33.9 g of water per 100 g of keratin. The state of the absorbed water is discussed. Clustering of water molecules takes place only above the threshold water conte

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070405

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe kinetics of denaturation of DNA have been studied by relaxation techniques. Examination of the terminal relaxation times for a variety of DNA's under a variety of conditions has shown that DNA denaturation is principally a hydrodynamically limited process. Measurements within the helix–coil transition have demonstrated that the experimentally measured terminal relaxation times are a function of the following: (1) position in the helix–coil transition; (2) ionic strength of the solvent; (3) solvent viscosity; (4) DNA concentration; (5) molecular weight; (6) number and position of single‐strand breaks. The dependence of the terminal relaxation time on the above mentioned factors can be attributed to hydrodynamic effects. Thus a hydrodynamic model for DNA unwinding is required. The model which best fits the data involves the assumption of a rotational frictional coefficient independent of molecular weight. This assumption is suggested by the fact that the relaxation time is proportional to the first power of the molecular w

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070406

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

年代:1969

数据来源: WILEY

摘要:

AbstractSodium counterion association with partially neutralized poly(D‐glutamic acid) or poly(DL‐glutamic acid) was measured by use of Wall's transference method with radioactive sodium. In the region where both polyacids are in completely random coil form, fractions of association were considerably less than that with poly(acrylic acid) in the same region of degree of neutralization. Even in the region where poly (D‐glutamic acid) is in the helical form, the fraction of association was less than that with poly(acrylic acid) in the same region. No pronounced characteristics attributable to counterion association corresponding to the helix–coil transition could be found. The association phenomena were discussed on the basis of a rodlike model of polyelec

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070407

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

年代:1969

数据来源: WILEY

摘要:

AbstractEquations were determined for the dependency of the melting temperature (Tm) of DNA upon the logarithm of the sodium ion concentration, for four DNA samples of widely different base compositions (θGC). The slopes of theseTmversus logMequations wore found to decrease with increasing θG Cof the samples. An empirical equation relatingTm, logM(Na+) and θG Cwas derived, which also accounts for differences inTmversus logMslopes. Data from the literature for some synthetic polynucleotides and for the crab(Cancer pagarus) satellite poly AT are discussed in relation to the above finding. The changes inTmversus logMslopes with θG Care interpreted in terms of changes in the thermodynamic parameters ΔSand ΔHwith base compos

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070408

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

年代:1969

数据来源: WILEY

摘要:

AbstractOptical rotatory dispersion (ORD) and circular dichroism (CD) measurements were carried out on a block copolymer, (γ‐ethylDL‐glutamate)160(L‐Trp)32, in which the tryptophan sequence has been modified to various extents by using 2‐nitrophenylsulfenyl chloride. The CD spectrum of the completely modified copolymer exhibits bands in some of the regions of maximum absorption of the sidechain chromophores. In the peptide absorption region the spectrum is similar to that reported in the literature for polypeptides in the α‐helical conformation. When the extent of modification of the tryptophan sequence is progressively reduced, there is a gradual change in the ORD spectra of the copolymers. On the basis of these data the assumption was made that no conformational change occurs on proceeding from the pure unmodified tryptophan sequence to the completely modified sequence. The results are discussed in connection with the study of possible conformational effects arising from selective chemical modification of tryptophan residues

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070409

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

年代:1969

数据来源: WILEY

摘要:

AbstractDilatometric measurements were made to determine the change in apparent specific volume φ of DNA resulting from thermal denaturation in neutral solution, φ increased continuously with temperature in the range 10–85°C. No deviations from a monotonically rising curve were observed in the φ versus temperature profile in the region of the melting temperature. The results are interpreted in terms of a partial loss of the preferentially bound DNA hydration shell. The nature of the well known buoyant density difference between native and denatured DNA was investigated by evaluating the densities in a series of cesium salt gradients at constant temperature. Extrapolation of the results to zero water activity indicates that the partial specific volumes of anhydrous native and denatured DNA are equal. The density difference at nonzero water activities is attributed to decreased hydration in the denatured state. The absence of a related change in φ accompanying the denaturation in the dilatometric experiments suggests that the probable volume change associated with loss of bound water during denaturation is accompanied by other compensatory volume effects. The possible nature of these volume effects is dis

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070410

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

年代:1969

数据来源: WILEY

摘要:

AbstractMeasurements of optical rotatory dispersion (ORD) and circular dichroism (CD) have been made in the range of 600‐210 mμ for the β‐glycan carbanilates as for instance, 2,3,6‐tricarbanilylcellulose (I), 2,3,6‐tricarbanilylmannan (II), 2,3‐dicarbanilylcellulose (III), and octacarbanilylcellobiose (IV) and also for the α‐glycan carbanilates, such as 2,3,6‐tricarbanilylamylose (V), tricarbanilylpullulan (VI), 2,3‐dicarbanilylamylose (VII), and octacarbanilylmaltose (VIII). Furthermore, the 2,3,4,6‐tetracarbanilyl‐α‐methyl‐glucopyranoside (IX) and the 1,2,3,4,6‐pentacarbanilylglucose (X) have been measured in dioxane at 20°C. For the β‐glycans a small negative CD in the region of 238–240 mμ and nearly symmetrical ORD curve with a crossover point at 238–240 mμ are found; this indicates a simple negative Cotton effect. In the case of α‐glycosides, a strong negative CD with a maximum at 240–242 mμ and a strong positive CD with a maximum at 223–225 mμ were found; the ORD curves are asymmetrical and cross the abscissa in two places, at 241–243 and 220–222 mμ. With 2,3,4,6‐tetracarbanilyl‐α‐methylglucoside (IX) no CD and ORD in the ultraviolet region and with 1,2,3,4,6‐pentacarbanilyl‐glucopyranoside (X) the ORD, but not the CD, could be measured. The ORD curve is nearly symmetrical, like those of the β‐glycans but is of opposite sign. It seems impossible to discuss the striking difference of the CD and ORD spectra between the α‐and the β‐glycans in terms of contributions of single independant chromophores influenced by their individual different steric arrangements and their spatial relation to the glycosidic bond in C1. The exciton theory of Moffitt, which is suitable for explaining the ORD and CD spectra of helical polymers, has been applied to α‐ and β‐glycans. A structure with helical parts is proposed f

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070411

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

年代:1969

数据来源: WILEY