ISSN:0006-3525    

DOI:10.1002/bip.1966.360040102

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe analogy, in both the thermodynamics and the kinetics, of reversible polymerizations on templates (in the case wherein these are catalyzed by exoenzymes) to helix–coil transitions (in the case where these proceed only from one end of each macromolecular chain) is presented. A suggestion, based on this analogy, is made concerning the possible nature of biological control of synthesis of macromolecules (enzyme induction and repression). The equations governing the kinetics of these one‐dimensional cooperative processes are presented and their solutions discus

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040103

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe equilibrium and the stoichiometry for the reversible complexing of silver ion by DNA have been studied by potentiometric titrations, proton release pH‐stat titrations, and by spectrophotometry. The complexing reactions involve primarily the purine and pyrimidine residues, not the phosphate groups. There are at least three types of binding (types I, II, and III), of which the first two have been intensively studied in this work. The sum of type I and type II binding saturates at one silver atom per two nucleotide residues. In the type I and type II reactions, zero and one proton, respectively, are displaced per silver ion bound. At pH 5.6, the reactions occur stepwise, type I being first, while at pH 8.0, they occur simultaneously. The silver ion binding curve is very sharp at pH 8, indicating a cooperative reaction. The strength of the binding increases with increasing GC content. Type I binding is more important for GC‐rich DNA's than for GC‐poor ones. Denatured DNA binds more strongly than does native DNA. The silver ion complexing reaction is chemically and biologically reversible. We propose that type II binding essentially involves the conversion of an\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm N} - {\rm H} \cdots {\rm N} $\end{document}hydrogen bond of a complementary base pair to an N—Ag—N bond. The nature of type I binding is less clear, but it may involve a π interaction with stacked bases. The buoyant density (ρ0) of DNA in a Cs2SO4density gradient increases when the DNA reacts with silver ion. The buoyant density change is about 0.15 g./ml. for 0.5 silver bound per nucleotide. The large buoyant density changes and the selective nature of the complexing reaction make it possible to perform good separations between native and denatured DNA or between GC‐rich and GC‐poor native DNA's by density gradient

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040104

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe neighbor–neighbor interactions in the small ribotrinucleotide ApApCp were investigated with the aid of optical rotatory dispersion measurements. This trinucleotide shows a Cotton effect between 220 and 325 mμ, in the region of its maximum ultraviolet absorption. The specific rotation of the trinucleotide is independent of concentration while the magnitude of the Cotton effect (levorotation) decreases markedly with increasing temperature. Such effects were not observed with the component nucleotides alone, in a simulated hydrolysis mixture, nor with the hydrolyzed trinucleotide. The Cotton effect is attributed to perturbation of the nucleotide base chromophores by neighbor–neighborintramolecular interaction (stacking), without any hydrogen bonding being involved; this interaction decreases with increasing temperature because of increased internal rotational freedom about the single bonds of the backbone chain with an accompanying disruption of the neighbor–neighbor interaction between the bases. This explanation is supported by a statistical mechanical theory of neighbor‐neighbor interactions in polynucleotides, involving the forces between the bases. Application of this technique to further studies of polynucleotides and polypeptides is d

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040105

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe change of the specific Kerr constant upon the addition of several acids to poly‐γ‐benzyl‐L‐glutamate solution in ethylene dichloride has been measured by the rectangular pulse method. The addition of a small amount of strong acid (trifluoroacetic acid, trichloroacetic acid, monochloroacetic acid, or hydrogen chloride) caused a rapid decrease of the specific Kerr constant. On the other hand, the effect of weak acids (formic acid, acetic acid, and propionic acid) was small. These facts show that the apparent dipole moment of a helical poly‐γ‐benzyl‐L‐glutamate molecule is considerably diminished by the protonation of terminal peptide groups. The electric conductivity of poly‐γ‐benzyl‐L‐glutamate solution in ethylene dichloride–dichloroacetic acid mixtures has been measured. It was found that the specific conductivity per unit concentration of poly‐γ‐benzyl‐L‐glutamate increased considerably at small fractions of dichloroacetic acid. This shows that poly‐γ‐benzyl‐L‐glutamate can react as a base (proton acceptor) with dichloroacetic acid. Thi

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040106

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

年代:1966

数据来源: WILEY

摘要:

AbstractA study of silver‐ion binding by nucleic acids and synthetic ribo and deoxyribopolynucleotides, has been carried out by means of potentiometric titration, thermal transition, and difference spectra. It is clearly demonstrated that a strong complex between Ag+and nitrogen atoms of bases is made reversibly. Binding constants and site numbers are determined for each type of polynucleotide. Base reactivity varies strongly with chain length, and a cooperative phenomenon is found in each case. Two successive complexes with DNA are seen in all the three techniques, and they have the same characteristics as complexes with respectively poly‐dGC and poly dAT. In the first complex, Ag+is linked to four bases, provided two of them are a G‐C pair. Calculated and experimental values of site numbers agree very well for DNA of different G‐C content. Thermal stabilization occurs simultaneously, and the increase of melting temperature corresponds to calculated changes of stacking energy between base pairs. In the second complex a new ordered structure insensitive to temperature is formed, with simultaneous release of protons. The stoichiometry can be related to base sequence. Complexing with silver increases the resistance of TMV RNA to both temperature and ribonuclease; a tentative explanation is given in the latt

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040107

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe theory of kinetics of polynucleotide synthesis at oligomeric templates is developed. It is shown that the dependence of oligomer efficacy on its size cannot be explained without taking into account the probability of separation of the oligomer from the growing chain. If such a possibility exists, the maximal size which can be achieved by the growing chain is determined by the ratio of the probability of proposed propagation and of the probability of separation. Without any models of the separation mechanism, the study of experimental kinetic data shows that two such mechanisms exist. Very short oligomers can be easily separated from the growing chain, but there is a critical size of oligomer after which the probability of separation is much smaller. The oligomers whose size is equal to or greater than the critical one form helices with growing chains.

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040108

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe results of the application of a modified polarographic method to the study of binding of thallous ions in solutions of pepsin are reported. Isoionic solutions of pepsin were converted by using a cation exchange resin to solutions of thallous pepsin. The extent of ion binding was obtained as in the case of cadmium pepsin by assuming that only free, i.e., unbound, ions contribute to the diffusion and migration currents, respectively. However, the relations used previously for computing the degree of ion binding have been refined on the basis of experience acquired in a parallel study of solutions of thallous acrylate and polyacrylate, respectively.

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040109

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

年代:1966

数据来源: WILEY

摘要:

AbstractPoly‐L‐arginine was prepared by the guanidization of poly‐L‐ornithine with 1‐guanyl‐3,5‐dimethylpyrazole. The poly‐L‐ornithine was derived from poly‐δ,N‐trifluroacetyl‐L‐ornithine by removal of the blocking groups under mild basic

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040110

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe electronic absorption and circular dichroism spectra of the complex formed by acridine orange with poly‐α,L‐glutamic acid in the α‐helix conformation have been measured in aqueous solution over a range of glutamate residue‐to‐dye ratios. Three Cotton effects (circular dichroism bands) associated with the long wavelength absorption band of acridine orange at 4950 A. are induced by complex formation between the dye and the polypeptide, and further circular dichroism bands are observed in the ultraviolet region associated with the 2700 A., but not with the 2950 A. absorption band of the dye. The induced optical activity is found to be relatively insensitive to the glutamate residue‐to‐dye ratio and to be more dependent upon the ionic strength of the solution. By Measuring the circular dichroism spectrum of the complex in aqueous solution under streaming conditions with the light propagated along the direction of flow the observed circular dichroism bands are assigned to electronic transitions polarized parallel or perpendicular to the axis of the polypeptide α‐helix. From the spectroscopic data it is inferred that the dye aggregate in theL‐PGA–AO complex has the form of a left‐handed superhelix bound to the core of the right‐handed α‐helix of poly‐α,L‐glutamic acid. It is shown that the longer and the shorter of the in‐plane axes of the dye molecule are probably orientated respectively at a small angle, and radially, with respect to th

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040111

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

年代:1966

数据来源: WILEY