摘要:

AbstractUltaviolet absorption spectra down to 185 mμ are presented for a number of nucleic acids and synthetic polynucleotides in the helical and random forms, and of their constituent mononucleotides, as well as the corresponding nucleosides and free bases. A short wavelength absorption band is in all cases observed with a maximum varying between about 187 and 201 mμ. These bands are more intense than those near 260 mμ. The helical polymers show a hypochromic effect in this region of a somewhat similar magnitude to that in the 260 mμ region. Other spectral phenomena accompanying denaturation and degradation are descri

ISSN:0006-3525    

DOI:10.1002/bip.360010302

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

年代:1963

数据来源: WILEY

摘要:

AbstractThe inactivation of sRNA by reaction with formaldehyde has been reported as it occurs under various conditions giving differing amounts of secondary structure. The theory of inactivation of an active macromolecule by a chemical reaction is developed. Results obtained with a partially melted out secondary structure show that formaldehyde inactivates sRNA by a single reaction at any one of about ten sites, while reaction at other sites does not affect the activity of the sRNA. In the presence of Mg++at neutral pH, a large proportion of the active molecules are completely protected against inactivation. From the correlation between the amount of secondary structure and the difficulty of inactivation, it is shown that at least a portion of the secondary structure of sRNA is essential to its amino acid acceptor ability. A comparison of results of various workers shows that formaldehyde does not alter RNA as drastically as other reagents and thus enables more discrimination between sites of reaction which are essential and those which are not essential to biochemical activity.

ISSN:0006-3525    

DOI:10.1002/bip.360010303

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

年代:1963

数据来源: WILEY

摘要:

AbstractStudies of different preparations of ribonuclease A by thin film dialysis and countercurrent distribution have shown the existence of conformational isomers. These forms are slowly interconvertible in a particular solvent environment. They show the minimum molecular weight of ribonuclease and do not differ enzymatically or by rotatory dispersion.

ISSN:0006-3525    

DOI:10.1002/bip.360010304

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

年代:1963

数据来源: WILEY

摘要:

AbstractExplicit expressions for theDKandRKassociated with the excitation of regular oligomers from their ground states to theKth exciton state as functions ofN, P,μ, μ∥, μt, and μrhave been derived on the assumption that the only perturbationVijto theNsingly excited states results from exciton transfer between adjacent residues,V12. TheDKrelation predicts the occurrence of a perpendicularly polarized absorption band arising from μ⟂ and a parallel polarized band from μ∥ with maxima atK= [2(N+ 1)/P] and 1, which are shifted from the monomer band by 2V12cos(2π/P) and 2V12cos[π/(N+ 1)], respectively. Overlapping of the bands, which may occur in oligomers, decreases rapidly withN, leaving two perfectly polarized bands in the polymer. Within each band which includes only a few levels near the maxima, the most probable transition may be associated with all of the intensity for very short chains but only 40.2–50% (⟂) and 80.9% (∥) asN→ ∞ (polymer case). A relation was derived by whichV12may be simply calculated fromμ, μr, μt, μ∥,a, andz. The nearest neighbor theory was compared with experiment by calculating a reasonable set of the relevant parameters which exactly acco

ISSN:0006-3525    

DOI:10.1002/bip.360010305

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

年代:1963

数据来源: WILEY

摘要:

AbstractThe effect of magnesium ion binding on the dissociation of side chain carboxyl group in α‐poly‐L‐glutamic acid has been measured by a modified titration technique involving pretitration of the polyacid with a strong base of a weakly bound counterion followed by addition of aliquots of the neutral salt of the more strongly bound counterion, magnesium chloride. The changes in the ionization of the carboxylic acid groups in the poly‐L‐glutamic acid side chains have been measured as a function of both the degree of preionization and of the concentration of magnesium chloride added. These changes have been related to changes in the polymer configuration (helix‐coil transition) as a function of degree of pre‐ionization. The effects of ionic strength and of ion binding have been determined by a comparison of tetramethyl ammonium chloride and of magnesium chloride at the same ionic strength. The plot proposed by Wada has been used to determine the pure helical region, the region of helix‐coil transition, and the pure coil region with both magnesium chloride and tetramethyl ammonium chloride as added salts. At the same ionic strength the effects produced by magnesium chloride addition are far greater than for tetramethyl ammonium chloride. Magnesium chloride at an ionic strength of 0.25 × 10−4produces an effect equivalent to that of tetramethyl ammonium at an ionic strength of 15.0 × 10−4. This effect is also apparent when the concentration of carboxyl groups ionized by magnesium chloride addition is determined. The much larger effects produced by the magnesium ion are attributed to the enhanced binding of this ion. The results reported indicate binding is favored in the helical configuration. The binding in the random coil configuration is similar to that reported previously for other randomly c

ISSN:0006-3525    

DOI:10.1002/bip.360010306

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

年代:1963

数据来源: WILEY

摘要:

AbstractOptical rotatory dispersion and infrared studies made on solutions of poly‐1‐benzyl‐L‐histidine (PBLH) in the solvent system chloroform–dichloroacetic acid (CHCl3DCA) indicate that this polymer exists in three different forms depending upon the solvent composition. These forms are reversibly interconvertible. Form I (PBLH‐I) exists in 100% CHCl3, form II (PBLH‐II) in CHCl3containing one residue equivalent of DCA (the histidyl‐DCA salt) and form III (PBLH‐III) in CHCl3with a large excess of DCA. It is suggested that PBLH‐I is an unionized random chain, PBLH‐II is an ionized “left‐handed” α‐helix, and PBLH‐III is an ionized random chain. Some optical rotatory dispersion and infrared measurements are reported for poly‐L‐histidine. A marked change in specific rotation of this polypeptide occurs i

ISSN:0006-3525    

DOI:10.1002/bip.360010307

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

年代:1963

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360010301

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

年代:1963

数据来源: WILEY