摘要:

AbstractThe hydrogen‐bonded structures of Ac‐Gly‐L‐Ala‐Gly‐NHMe have been studied by theoretical conformational analysis. The geometric parameters and energies of stable forms with various combinations of 3 → 1 and 4 → 1 type hydrogen bonds have been calculated. The stable conformations found can be used as canonical forms in the investigation of linear and cyclic peptide compounds with intramolecular

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130602

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe helix–coil transitions of poly(Nε‐methyl,Nε‐carbobenzoxy‐L‐lysine), poly(Nδ‐methyl,Nδ‐carbobenzoxy‐L‐ornithine), and poly(Nδ‐ethyl,Nδ‐carbobenzoxy‐L‐ornithine) in chloroform–dichloroacetic acid and their corresponding decarbobenzoxylated polypeptides in alkaline solutions were followed by optical rotation measurements. The introduction of a methyl or an ethyl group to the side chains of the carbobenzoxy derivatives of poly(L‐lysine) and poly(L‐ornithine) appeared to weaken the helical conformation at 25°C. The thermodynamic quantities of the three water‐soluble polypeptides were calculated from the data on potentiometric titrations at several temperatures. For uncharged coil‐to‐helix transition, ΔH= −370 cal/mol and ΔS= −1.1 eu/mol for poly(Nε‐methyl‐L‐lysine), and ΔH= −540 cal/mol and ΔS= −1.6 eu/mol for poly(Nδ‐ethyl‐L‐ornithine) (all on molar residue basis). The absolute values of ΔHand ΔSdropped in the region of pH‐induced transition and eventually both quantities became positive. The initiation factor σ was about 2 × 10−3, which was essentially independent of temperature. For poly(Nδ‐methyl‐L‐ornithine) the coi

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130603

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

年代:1974

数据来源: WILEY

摘要:

AbstractUncharged poly(Nε‐methyl‐L‐lysine) (PMLL) and its isomer, poly(Nδ‐ethyl‐L‐ornithine) (PELO), in alkaline solution (pH ca. 12) undergo a helix‐to‐β transition upon mild heating at 50°C or higher in a manner similar to that of poly(L‐lysine) (PLL). The rate of conversion follows the order: PMLL

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130604

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

年代:1974

数据来源: WILEY

摘要:

AbstractPoly(Nδ‐carbobenzoxy,Nδ‐benzyl‐L‐ornithine) (PCBLO) was prepared by the standard NCA method. PCBLO was converted into poly(Nδ‐benzyl‐L‐ornithine) (PBLO) through decarbobenzoxylation with hydrogen bromide. The monomerNδ‐benzyl‐L‐ornithine was synthesized by reactingL‐ornithine with benzaldehyde, followed by hydrogenation. The conformation of the two polypeptides was studied by optical rotatory dispersion and circular dichroism. PCBLO forms a right‐handed helix in helix‐promoting solvents. In mixed solvents of chloroform and dichloroacetic acid (DCA) it undergoes a sharp helix–coil transition at 12% (v/v) DCA at 25°C, as compared with 36% for poly(Nδ‐carbobenzoxy‐L‐ornithine) (PCLO). Like PCLO, the helix–coil transition is “inverse,” that is, high temperature favors the helical form. PBLO is soluble in water at pH below 7 and has a “coiled” conformation. In 88% (v/v) 1‐propanol above pH (apparent) 9.6 it is completely helical. In 50% 1‐propanol the transition pH (apparent) is about 7.4; this compares with a pHt

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130605

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

年代:1974

数据来源: WILEY

摘要:

AbstractA previously described procedure for simultaneous optimization of bond lengths and angles was used to test different models for mannan I. Potential hydrogen bonds and the glycosidic angle were included in the optimization. A conformational model with bifurcated intramolecular hydrogen bonds of the type observed in the methyl cellobioside methanol complex showed the best agreement with available exprerimental data. The coordinates of this model were provided by computer calculations. The available X‐ray data, however, were not sufficient for selecting this model; rather, ir data were necessary to furnish the needed information. The different conformational models tested all showed an almost constant virtual bond lengthO(1)–O(4) of the β‐pyranose residue. This was in contrast to the previously obtained results for the α‐pyranose

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130606

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe binding of ethidium bromide to DNA has been studied by various optical methods. From fluorescence polarization studies, and film, electric linear dichroism, and circular dichroism spectra, we propose assignments of the absorption bands of the dye, which are discussed in connection with wave‐mechanical calculations recently reported.The optical activity induced in the dye absorption bands upon binding to DNA was attributed to various origins depending on the electronic transition considered. The visible absorption band displayed a circular dichroism due to the asymmetry of the binding site and independent of the amount of binding. The transition identified at 378 nm from the circular dichroism and electric dichroism observations was thought to be due to a magnetic‐dipole transition. It remained constant with increasing amounts of dye bound. The main ultraviolet band showed circular dichroism characteristics corresponding to exciton interactions between dye molecules bound to neighboring sites.The electric dichroism observed for the strongly bound dye molecules indicated that the phenanthridinium ring of ethidium bromide was probably not perfectly parallel to the DNA base planes. When the amount of dye bound to DNA exceeded the maximum amount compatible with the exclusion of adjacent binding sites, the electric dichroism decreased owing to the appearance of externally bound dye molecules with no contribution to the dichroism.Sonicated DNA was used to study the lengthening of the DNA molecule upon complexation. Although the viscosity of the complexes increased with the amount of binding, the rotational diffusion coefficient measured by the electric birefringence relaxation was not detectably affected. The absence of variation in the electric birefringence with the binding indicated that the DNA base stacking remained unalte

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130607

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

年代:1974

数据来源: WILEY

摘要:

AbstractIn order to study the effect of side‐chain length on the conformation of polypeptides, conformational changes of various ionic polypeptides with various lengths of side chain, poly‐Nε‐glutaryl‐L‐lysine (PGL), poly‐Nδ‐glutaryl‐L‐ornithine (PGO), poly‐Nε‐succinyl‐L‐lysine (PSL), and poly‐Nδ‐succinyl‐L‐ornithine (PGO), were investigated by ORD, potentiometric titration, and dilatometric measurements in aqueous solution. The results of optical rotation and potentiometric titration measurements indicate strongly that the α‐helix stability increases in the sequence PSO

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130608

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe helix–coil transition of poly‐N5‐(2‐hydroxyethyl)L‐glutamine (PHEG) in aqueous isopropanol was examined by means of optical rotatory dispersion (ORD) and intrinsic viscosity [η] measurements. The Zimm–Bragg parameters σ andsfor the transition were determined from the ORD data as a function of molecular weight. It was found that the transition was characterized by a relatively low cooperativity; the values of\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt \sigma $\end{document}were in the range from 0.039 to 0.066, depending on the solvent composition. These σ values are much larger than those reported for other polypeptide–solvent systems. The transition enthalpy was negative and its magnitude varied with the solvent composition, with a maximum of 620 cal/mol at 40 wt% isopropanol. The curve of [η] versus helical content for a high‐molecular‐weight sample exhibited a very broad minimum, and this behavior was attributed to the low cooperativ

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130609

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe longitudinal proton magnetic relaxation timesT1were measured for ferri (met)‐and carbonmonoxy‐bovine haemoglobin and equine myoglobin in 0.1MKH2PO4aqueous solutions near pH 6 at 5°C and 35°C from 1.5‐ to 60‐MHz Larmor frequencies. It is concluded that the correlation time τCfor the dipole–dipole interaction of electron and nuclear spins is in fact the electron (ferric) spin relaxation time τSbeing close to 1.5 × 10−10sec for both metHb and metMb at 5°C. At 35°C the paramagnetic relaxation rates are not determined solely by the relaxation of protons exchanging from the haem pocket with bulk solvent. Hence, τCat 35°C cannot be calculated from the dispersion data obtained at this temperature. The relevance of this for the determination of interspin di

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130610

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe conformational changes of poly‐Nε‐glutaryl‐L‐lysine (PGL) and poly‐Nε‐succinyl‐L‐lysine (PSL) in various salt solutions were studied by use of ORD and potentiometric titration measurements. The addition of alkali metal salts to the fully ionized PGL or PSL solution caused helix formation. The helical content of the polymers increases in the following sequences: at salt concentration 0–2M, CsCl

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130611

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

年代:1974

数据来源: WILEY