摘要:

AbstractThe values of maximum frequencies, intensities, and other spectral parameters of the main absorption bands of amino acid residue side‐chain groups have been obtained in the 1500–1800‐cm−1region for solutions in heavy water at pD 1–12. It is shown that absorption of residues of asparagine, glutamine, aspartic and glutamic acids, arginine, and tyrosine must be taken into account in quantitative studies of the infrared spectra of polypeptide and protein solutions in heavy water. Examples of separating out the amide I band for ribonuclease A in heavy water

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140402

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe conformation of the ribose‐phosphate unit for the four principal configurations of the sugar ring has been studied using the extended Hückel theory and the Lennard–Jones empirical potential. Initially, the oxygen atoms of the p3 and p5 groups were not taken into account. With this restriction, the energy of this residue with regard to the structure of RNA has been minimized for the rotational angles ψ and ϕ′.The equivalence of the sugar puckering C2′endo≃ C3′exoand C3′endo≃ C2′exohas been confirmed. We find that the role of the sugar configuration is important and that there is a difference in the rotations around the bond C3′‐O3′ (ϕ′ angle) according to this configuration. The C3′endosugar form seems to be energetically preferred for this residue of RNA.The oxygen atoms and the electrostatic interactions were then introduced into the empirical potential. The variation of the energy when varying ϕ′ for different positions of the p5 group was studied for the main C3′endoand C2′endoconfigurations of the sugar; in this condition the ϕ′ rotation is considerably restricted but the allowed regions continue to differ according to

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140403

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

年代:1975

数据来源: WILEY

摘要:

AbstractDetailed inelastic, incoherent neutron‐scattering (INS) spectra are presented for poly‐L‐alanine in both the α‐helical and β‐sheet form. Assignments are made from previous normal coordinate calculations. Of particular interest is the methyl torsion at 230 cm−1, which is the strongest peak in the spectrum and is independent of backbone conformation. The height of the potential barrier for methyl group rotation is calculated to b

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140404

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

年代:1975

数据来源: WILEY

摘要:

AbstractCyclic peptides containing sarcosine, cyclo‐(Pro‐Sar‐Gly)2, cyclo‐(Sar‐Sar‐Gly)2, cyclo‐(Sar4), and cyclo‐(Sar6) have been synthesized by the cyclization of thep‐nitrophenyl ester of linear peptides. Thetert‐butoxycarbonyl group was used as theNα‐protecting group, which was removed by acid. Benzyl ester was used to protect theC‐terminal.tert‐butoxycarbonylpeptide was obtained by the stepwise elongation of the peptide bond by the carbodiimide method. Deblocking and cyclization of the linear peptide

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140405

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe interaction between cyclic peptides [cyclo‐(Sar4), cyclo‐(Pro‐Sar‐Gly)2, cyclo‐(Sar‐Sar), and cyclo‐(Sar‐Gly)] with benzene has been investigated by nmr spectroscopy. The experiment with cyclo‐(Sar4) showed that benzene interacted preferentially with thetranspeptide bond in a similar manner to the dimethylformamide–benzene interaction. The solvent‐induced nmr shift was then applied to the conformational analysis of cyclo‐(Pro‐Sar‐Gly)2with the aid of the molecular model. The major conformation was proved to possess the C2symmetry with internally hydrogen‐bonded glycine residues, in which all peptide bonds weretrans. The interaction of cyclo‐(Sar‐Sar) and cyclo‐(Sar‐Gly) with benzene was also studied. The association constant was 0.115‐kg solution per mole of cyclo‐(Sar‐Sar) and 0.089‐kg solut

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140406

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe high‐resolution (300 MHz) proton nmr spectrum ofE. colitRNAfMethas been examined in 0.17MNaCl, with and without Mg2+, and at various temperatures. In light of recent studies of otherE. colitRNA and fragments of tRNAfMet, some low field (11–15 ppm) resonances previously assigned to secondary structure base pairs are reassigned to a tertiary structure A14–S4U8base pair and a protected uridine residue in the anticodon loop. These two resonances and other low field resonances which are assigned to secondary structure base pairs are used to monitor the thermal unfolding of the molecule. In the absence of Mg2+the tertiary structure base pair is present only to ∼45°C, but in the presence of Mg2+it remains until at least 70°C. Analysis of the temperature dependence of other low field resonances indicates that the melting of the dihydrouridine stem occurs more or less simultaneously with the loss of tertiary structure. The observation of the resonance from the A14–S4U8base pair proves that tertiary structure is present in this molecule below 40°C, even in the abs

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140407

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe relaxation kinetics of a staggering zipper model are presented, in which the formation of helical nuclei is regarded to be rate‐limiting and in which the sliding of strands along the helices is prohibited. Instead a realignment of staggered chains is only possible via complete uncoiling. While maintaining the third order of the initial reaction as in an all‐or‐none mechanism, the model predicts a large range of relaxation times, which contribute to the mean relaxation time according to the stability of the individual species and which are weakly coupled in the range of small amounts of helical content. The model can easily be compared to experimental results and agrees well with relaxation data obtained from a triple‐helical peptide fragment of collagen. It may be readily expanded to other multistranded helix ⇄ coil transitions with steady‐state formation of the individual species and it suggests that the fraying of the helix ends is hidden by the fast‐relaxation times due to the equilibration of the shortest he

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140408

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

年代:1975

数据来源: WILEY

摘要:

AbstractInteraction between the sodium salt of a DNA extracted from salmon sperm (41% GC) with [Pt(NH3)4]Cl2, [Pt(NH2(CH2)2NH(CH2)2NH2Cl]Cl,cis‐Pt(NH2(CH2)2NH2)Cl2,cis‐Pt(NH3)2Cl2,trans‐Pt(NH3)2Cl2, K[Pt(C2H4)Cl3], and K2[PtCl4) indicates at least three types of complexation. A correlation is found between the change of pH and the number of platinum atoms fixed per (AT + GC) unit. The first binding site is located on the G‐C pairs (guanine–cytosine), most likely the N‐7(G) site, as it was shown in a previous study of the guanosine‐platinum salts. The fixation of the second platinum atom by the pair (AT + GC) takes place with liberation of protons. In the case of the complexescis‐Pt(NH2(CH2)2NH2)Cl2,cis‐Pt(NH3)2Cl2, andtrans‐Pt(NH3)2Cl2the second interaction seems to involve simultaneously the N‐7(A) and the N‐1(G) and N‐3(C) sites. This latter intercrosslink between guanine and cytosine obviously liberates protons and the decrease of pH is related in this case to thetranseffect of the platinum compounds. The first two platinum atoms in the reaction of K2PtCl4] or the Zeise salt, K[Pt(C2H4)Cl3] with DNA are fixed on the G‐C pairs. A maximum of six platinum atoms per (AT + GC) unit were fixed in this case. Preliminary experiments with a DNA extracted from bacteriaMicrococcus

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140409

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe heat capacities ofL‐Alanine, tri(L‐alanine), and poly (L‐alanine) (α helicoidal form and β pleated sheet structure) have been measured between 1.5 and 300°K with a standard adiabatic calorimeter.In the solid state, the heat capacity is in general dut to three parts which are additive in first‐order approximation. (1) The lattice vibrations or “acoustical modes” which are the largest at low temperatures. The low‐temperature lattice specific heat is proportional toT,T2, orT3for an ideal one‐, two‐ or three‐dimensional solid, respectively. (2) The so‐called group vibrations or “optical modes” which, due to their high frequencies, usually take effect only at higher temperatures. (3) The defects and unharmonic effects.The α‐amino acid and its trimer present a specific heat thermal variation characteristic of molecular solids which is correctly fitted with an empirical law proposed by Kitaigorodskii. This author assumes that, for such solids, the molecular lattice point has six degrees of freedom (three of translation and three of rotation). Thus the lattice contribution of the specific heat satisfies the Debye approximation in agreement with the doubling of the number of degrees of freedom per molecule (compared with atomic crystals).The polypeptide behavior is, however, different. The specific heat for each form exhibits a thermal dependence connected with a strong vibrational anisotropy. The model proposed earlier by Tarasov accounts well for these results. In the case of the β form, we have observed the predicted three‐ and two‐dimensional behavior due to the intermolecular H bondings responsible for the sheet structure. For the α form we observed a one‐dimensional pattern at higher temperature, since each peptidic chain vibrates separately.The comparison with other spectroscopic and theoretical investigations shows a large discrepancy. However, we have attemped to account for the “optical contribution” to the specific heat of poly(L‐alanine) by using a continuum of mean frequencies as suggested by Wunderlich. Vibrational frequency spectra are proposed to explain our results, but the overlapping of acoustical and optical branches in the case of the α form outlines the limits of macroscopic models. It is quite likely that the acoustical spectrum is greatly affected by the intramolecular H bonding.At low temperature the specific heat is a physical property sensitive to the long‐range order of the macromolecule, and therefore further spectroscopic and theoretical investigations are necessary

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140410

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

年代:1975

数据来源: WILEY

摘要:

AbstractSpectrophotometric binding studies were undertaken on the interaction of neutral red with native and heat‐denatured, sonicated, calf thymus DNA in a 0.2Mionic strength buffer containing Tris–sodium acetate–potassium chloride at 25°C. The pKAof neutral red was found to be 6.81. At pH 5 the binding of protonated neutral red was complicated even at low concentration ratios of dye to DNA. In the pH range 7.5–8.5 the tight binding process could be studied and it was found that both protonated and free base species of neutral red significantly bind with DNA having association constants (in terms of polynucleotide phosphate) of 5.99 × 103M−1and 0.136 × 103M−1, respectively, for native DNA and 7.48 × 103M−1and 0.938 × 103M−1, respectively, for denatured DNA. The pKAvalue of the neutral red–DNA complexes were 8.46 for native DNA and 7.72 for denatured DNA. These results are discussed in terms of possi

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140411

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

年代:1975

数据来源: WILEY