摘要:

AbstractCollagen molecules can exist, in the aggregate crystalline state (C) and in solutions, as tropocollagen helices (H) or random coils (RC). We have compared the role of temperature, salt type, and salt concentration,C8, on the transformations: C → RC (I), H → RC (II), and H → C (III) under near‐isoelectric conditions. Processes I and II occur in the direction from ordered to disordered form on increasing temperature, while process III occurs in the direction crystal → dissolved helices on lowering temperature. The order of both anions and cations for increasing the stability of the dissolved random coiled form is similar for processes I and II, but the order of the anions for increasing the stability of the dissolved helices, according to process III, is reversed with respect to the Hofmeister series.TIandTIIare greatly and continuously depressed by some salts on increasingC8while, for other salts, they are at first slightly depressed and then raised.TIII, instead, is at first raised and then lowered on increasingC8. For a given salt the field of stability of each form is determined, on a pseudo‐phase diagram, by the relative positions of theTIversusC8, theTIIversusC8, and theTIIIversusC8, curves. The similarity of the effect of temperature, salt type, and concentration on processes I and II supports the contention that both processes are controlled by the interaction of the random coiled form with the salt solution. The phenomenon of crystallization by increasing temperature is complicated by large time effects and, often by lack of reversibility. Assuming, nevertheless, that there is an underlying equilibrium process, two possible interpretations are proposed. The peculiar trend of theTIIIversusC8curve is justified on the basis that it reflects the usual change from salting in to salting out on increasingC8, allowing for the fact that the dissolved phase is stable in the low‐temperature range. The reversal of the order of anions for process III can be most simply justified in terms of the slight cat ionic character of the tropocollagen units. Accordingly, the dissolved helices will be more; stable of the crystalline form depending upon the occurrence of a net charge different from zero on the protein, as well as upon low ionic strength and low temperature. Minute alterations of KCl concentrations are able to cause isothermal precipitation of fibers and probably constitute a controlling factor for the fibrog

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040902

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe intrinsic, viscosities at zero shear rate of defined complexes of proflavine, 9‐aminoacridine, and 9‐amino‐l,2,3,4‐tetrahydroaeridine with calf thymus DNA have been determined at, various ionic strengths by means of rotating cylinder viscometers. By controlled adjustment, of the composition of the mixtures, the amount of bound acridine (rmoles/g.‐atom DNA phosphorus) was maintained constant at different dilutions. The intrinsic viscosities of the complexes increased withrup torvalues (ca. 0.16–0.20) corresponding to the end of the process of strong binding of the acridinium cations. However, complex formation between the acridines and thermally denatured DNA caused either a marked decrease in viscosity (at the low ionic strengths of 0.0015 and 0.005) or no change at all (ionic strength 0.1). These results are discussed in the light of presently available hydrodynamic theories relating the intrinsic, viscosity of DNA to its molecula

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040903

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

年代:1966

数据来源: WILEY

摘要:

AbstractThree processes by which tropocollagen units associate to yield highly specific aggregates have been examined. From the temperature coefficients of the amounts aggregated it is concluded that the complex “native” aggregation is endothermic, whereas both end‐to‐end and lateral aggregation are exothermic. These results combined with additional information lead to the conclusion that “native” aggregation is an entropy‐driven process in which hydrophobic bonding plays the dominant role. In contrast the reactions producing the lateral aggregate and the aggregate in which end‐to‐end bonding is dominant are electrost

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040904

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe relaxation time of thyroglobulin has been determined in water at. neutral pH, in concentrated urea and guanidine solutions, at alkaline pH, both before and after reduction with β‐mercaptoethanol. The structure of thyroglobulin in concentrated urea solutions is markedly affected by the pH, Time‐dependent changes occur in thyroglobulin in concentrated urea or guanidine solutions which arc observable by polarization of fluorescence but not by optical rotation or viscosity. The reduction of the disulfide crosslinks of thyroglobulin in urea at high pH or in guanidine produces linear polypeptide chains with few if any permanent contacts between segm

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040905

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe effects of deuteration and of changes in solvent composition on the thermo dynamics of the helix–coil transition have been studied by calorimetric and optical measurements in the poly‐γ‐benzyl‐L‐glutamate–dichloroacetic acid–1,2‐dichloro‐ethanc system. For a given solvent composition, deuteration of the polypeptide and of the acid lowers the transition temperatureTc, while an increase in the volume fraction of acid in the solvent raises Tc. A rise in Tcis accompanied by a decrease in both the van't Hoff and the calorimetric heats of transition, but at different rates. The result is a temperature dependency in the Zimm‐Bragg cooperation parameter σ. Possible causes of this result and its impli

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040906

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe purpose of this paper is to examine and contrast several formulations of the partition function for the helix–coil transition of random‐sequence nucleic acids. In the exact approach, the sequence of bases in a given molecule is fixed, but this leads to expressions which are difficult to evaluate. Another approach is to make a summation over all possible sequences, each weighted by the probability of its occurrence, thereby in effect allowing all sequences to a given molecule. The error in this approach is that it does not guarantee that the average base sequence is random. This difficulty can, in principle, be overcome by applying successively increasing constraints on the system to ensure that all moments of the distribution are equal to the random‐sequence values. It is shown for the particular case of short molecules which melt only from the ends that the convergence of this method to the true solution is poor. The major conclusion is that composition fluctuations which cover a sizeable region of the molecule must be included in an accurate description of the melting trans

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040907

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

年代:1966

数据来源: WILEY

摘要:

AbstractBased on the four electrodes technique, an apparatus is described which measures the Very Low Frequency (VLF) conductivity of ionic solutions, all electrode effects being completely eliminated. It is thus possible to measure the conductivity frequency dependence between 0.8 and 500 cps, with a relative error of 10−4. Applying this method to DNA solutions, one always finds a conductivity dispersion in the VLF range, which disappears when the biopolymer is heat‐denatured. The relaxation time is different from one solution to another, but is always greater than 10 msee. approximately, sometimes even greater than 0.1 sec., the upper limit which one can estimate with our apparatus. The different, explanations of the DNA very low frequency polarization, assuming that its relaxation is connected with the rotational diffusion of the biopolymer long axis, is discus

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040908

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.1966.360040909

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.1966.360040910

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.1966.360040911

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

年代:1966

数据来源: WILEY