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1.
The circular dichroic properties of H-Gly-Phe-(Gly)n-Trp-Gly-OH (II, n = 0,1,2) and of related simpler peptides, such as H-Phe-Gly-OH, H-Gly-Phe-OH, H-Gly-Phe-Gly-OH, H-Phe-Trp-OH, H-Phe-Trp-Gly-OH, and H-Gly-Phe-Trp-OH in water and trifluoroethanol solutions are investigated. Peptides containing only one phenylalanyl residue show markedly different near-uv dichroic signals depending on whether this residue is in the N-terminal position or not. The possible origin of this feature is discussed. The study of the oligopeptides II (n = 0,1,2) shows that no strong intramolecular interaction between the two aromatic rings is present. However, the dichroic properties of II (n = 0) are clearly anomalous, and the analysis of H-Gly-Phe-Trp-OH, H-Phe-Trp-Gly-OH, and of H-Phe-Trp-OH at different pH's, confirms that the presence of two adjacent aromatic residues may bring about chiroptical properties which indicate a restriction in the conformational equilibrium of the molecule. The limits, and the possible generalization of this finding, are discussed.  相似文献   

2.
The fluorescence properties of several cooligopeptides of glycine, phenylalanine, and tryptophan, containing one or two aromatic residues, are investigated. In particular, a detailed analysis is made of the influence of pH upon the quantum yield and the position of the emission maximum (λmax) in H-Trp-Trp-OH, H-Trp-Gly-OH, H-Gly-Trp-OH, H-Gly-Trp-Gly-OH, H-Trp-Trp-OH, H-Trp-Trp-Gly-OH, H-Gly-Trp-Trp-OH, H-Phe-Trp-OH, H-Phe-Trp-Gly-OH, H-Gly-Phe-Trp-OH, and H-Gly-X-(Gly)n-Trp-Gly-OH, with X = Phe or Trp, and n = 0,1,2. It is shown that raising the pH from ca. 2 to 11 results in a red shift of λmax, and an increase in the quantum yield. These changes, mostly structure dependent, are in most cases attributable to electronic perturbations acting directly upon the λmax of the fluorophore(s) and upon the quenching efficiency of the free amino and carbonyl groups. For the compounds having two adjacent tryptophyl residues, it is shown that the two fluorophores do not appear to have the same emission properties and the quantum yield is lower than expected. The causes of this behavior are discussed in terms of conformational effects, stacking interactions, and radiationless energy transfer. Finally, an attempt is made to correlate fluorescence data with previous circular dichroism data which had indicated the occurrence of a conformationally rigid structure for some of the compounds having two adjacent aromatic residues.  相似文献   

3.
The conventionally protected oligopeptides of the two homologous series Boc-(L -Ile)n-OMe and Boc-(D -aIle)n-OMe (n = 2–6) were synthesized in a standard stepwise fashion and their uv and CD spectra in 2,2,2-trifluoroethanol, and solid-state ir spectra were investigated. In addition, two oligomeric products derived from the NCAs of L -isoleucine and of D -allo-isoleucine and having a DP of 20 and 12, respectively, were studied in the solid state by x-ray and ir. No substantial differences between the properties of the diastereomeric oligomers in the solid state were noticed, a β-structure being very likely at least for the Boc-protected hexapeptides and the higher oligomers. In contrast, differences were observed between the spectroscopic properties of the diastereomeric oligopeptides, and especially of the hexapeptides, in trifluoroethanol solution. The different properties of the hexapeptides in solution were related to the existence, in the case of Boc-(L -Ile)6-OMe, of soluble molecular aggregates in which the peptide chains assume the β-conformation. These results provide an additional example of the influence of the configuration of asymmetric carbon atoms of the side chains on the conformational properties of peptide molecules in solution.  相似文献   

4.
Critical chain length for helix formation in L-methionine oligopeptides   总被引:1,自引:0,他引:1  
J M Becker  F Naider 《Biopolymers》1974,13(9):1747-1750
The circular dichroism of a series of L -methionine oligopeptides [BOC-(Met)n-OMe] was examined in trifluoroethanol and hexafluoroacetone sesquihydrate. The results indicate that the trimer through the hexamer exists predominantly in disordered conformations in these solvents. An abrupt change in the CD pattern at the heptamer in trifluoroethanol suggests that L -methionine oligopeptides begin forming helices at this chain length.  相似文献   

5.
The preparation of the co-oligopeptides of the series H-Gly-Phe-(Gly)n-Trp-Gly-OH (n = 0, 1, 2) and of other free peptides of glycine, L -tryptophan, and L -phenylalanine is reported. The syntheses have been carried out by conventional methods, using N-hydroxysuccinimide esters for the coupling steps. The ultraviolet absorption properties of the free peptides have been investigated in water. No hypo- or hyperchromicity was found for the aromatic chromophores, with the exception of H-Gly-Phe-Trp-OH, which shows a small but significant hypochromicity. The contribution of the peptide bond to the molar absorptivity in the far ultraviolet has been separated from that of the side chain plus the ? COO? group by plotting the measured molar absorptivity ? of the farthest accessible uv maximum as a function of the number of peptide bonds (nA). The peptide bond contribution proved to be independent of nA in the range nA = 1–5, thus ruling out the onset of helical conformations in the longer chain peptides.  相似文献   

6.
V Rizzo  P Luigiluisi 《Biopolymers》1977,16(2):437-448
The influence of pH upon CD spectra of H-Trp-Trp-OH, H-Trp-Trp-Gly-OH, and H-Gly-Trp-Trp-OH is investigated and data are compared with those obtained for peptides containing only one tryptophyl residue. A negative Cotton effect at around 225 nm, which in previous work has been related to an increase of the conformational rigidity in compounds having the sequence -CO-Trp-Trp, is also observed in the case of H-Trp-Trp-OH and H-Trp-Trp-Gly-OH upon deprotonation of the terminal α-amino group. These data, together with observations arising from solvent and temperature effects, give evidence that H-Trp-Trp-OH undergoes a conformational change upon going from acid to alkaline conditions, where the two aromatic side chains become conformationally more rigid relative to each other. This rigidity generates an exciton coupling between the Bb transitions of the two indoles. Hydrophobic forces, including stacking interactions, do not appear important in stabilizing this conformationally rigid structure. Rather, intramolecular electrostatic interactions (e.g., hydrogen bondings or polar interactions between the aromatic side chain and the peptide backbone) as well as interactions with the OH group(s) of the solvent, are suggested to be the salient forces. Possible structures which obey these requisites are discussed.  相似文献   

7.
Z-Dehydrophenylalanine (ΔzPhe) possessing four oligopeptides, Boc-(L -Ala-ΔzPhe-Aib)n-OCH3 (n = 1–4: Boc, t-butoxycarbonyl; Aib, α-aminoisobutyric acid), were synthesized, and their solution conformations were investigated by 1H-nmr, ir, uv, and CD spectroscopy and theoretical CD calculation. 1H-nmr (the solvent accessibility of NH groups) and ir studies indicated that all the NH groups except for those belonging to the N-terminal L -Ala-ΔzPhe moiety participate in intramolecular hydrogen bonding in chloroform. This suggests that the peptides n = 2–4 have a 4 → 1 hydrogen-bonding pattern characteristic of 310-helical structures. The uv spectra of all these peptides recorded in chloroform and in trimethyl phosphate showed an intense maximum around 276 nm assigned to the ΔzPhe chromophores. The corresponding CD spectra of the peptides n = 2–4 showed exciton couplets with a negative peak at longer wavelengths, whereas that of the peptide n = 1 showed only weak signals. Theoretical CD spectra were calculated for the peptides n = 2–4 of several helical conformations, on the basis of exciton chirality method. This calculation indicated that the three peptides form a helical conformation deviating from the perfect 310-helix that contains three residues per turn, and that their side chains of Δz Phe residues are arranged regularly along the helix. The center-to-center distance between the nearest phenyl pair(s) was estimated to be ~ 5.5 Å. The chemical shifts of the ΔzPhe side-chain protons (Hβ and aromatic H) for the peptides n = 2–4 indicated anisotropic shielding effect of neighboring phenyl group(s); the effect also supports a regular arrangement of the Δz Phe side chains along the helical axis. © 1993 John Wiley & Sons, Inc.  相似文献   

8.
The conformations of oligopeptides derived from L -alanine and co-oligomers of L -alanine with γ-methyl-L -glutamate were studied in several solvents via optical rotation and far-ultraviolet spectroscopy. Calculated values for optical rotation based on model compounds were compared with experimental values for the oligomers. In trifluoroacetic and dichloroacetic acids, the oligomers and co-oligomers exhibit rotations in close agreement with predicted values based on model compounds. Thus, in these solvents only nonhelical conformations exist. In trifluoroethanol, the experimental points of molar rotation for the pentamer and larger oligomers no longer follow the predicted values. In addition, the benzyloxycarbonyl and acetyl cononamers show b0 values of about ?150, which demonstrates the presence of stable helical forms for these peptides. We also examined the molar extinction coefficients of oligopeptides in the 190 mμ region and determined the values for nonhelical peptide groups. The molar extinction coefficients per amide bond for the benzyloxycarbonyl and acetyl cononamers show extensive hypo-chromism, once again indicating the presence of stable helices for these compounds in trifluoroethanol.  相似文献   

9.
The preparation of the co-oligopeptides of the series H-Gly-Trp-(Gly)n-Trp-Gly-OH (n = 0, 1, and 2) and of a number of other unprotected co-oligopeptides of glycine and tryptophan is reported. The syntheses have been carried out by conventional methods, using, in general, N-hydroxysuccinimide esters for the coupling steps. All the oligopeptides were obtained after purfication as colorless and crystalline products, and gave only one spot on thin-layer chromatography. Specfic problems connected with the synthesis and purficiation of optically pure tryptophan-containing peptides are discussed.  相似文献   

10.
1H-nmr spectra for a series of Boc-L -(Met)n-OMe (n = 2–9) homo-oligopeptides have been observed in the helix-supporting solvent trifluoroethanol (TFE) at millimolar concentrations. Interfering solvent peaks were eliminated using two decoupling frequencies to selectively remove the methylene and hydroxyl protons of the solvent. Comparisons with specifically α-deuterated homo-oligopeptides gave complete assignments of the NH region of the Boc-Metn-OMe oligomers up to the heptapeptide. Analysis of chemical shifts, coupling constants, and temperature dependence of chemical shifts suggests that up to the hexapeptide, similar structures exist in deuterochloroform and TFE. In contrast, nmr parameters at the heptapeptide for several internal residues differ in these solvents. These results suggest that a C7 to α-helix transition may occur in TFE as the chain length of the methionine oligopeptides increases.  相似文献   

11.
A conformational analyis of co-ologopeptides containing methionine and valine or methionine and glycine was carried out using circular dichrosim. The oligopeptides containing valine and methionine (dimer to hexamer) are disorder in hexafluoropropane diol·0.5 H2O and trimethyl phospate but become helical in trifluoroethanol at the heptamer. The CD spectra for hesamers and heptamers containing methionine or methionine and one valine give evidience that one valyl residue can be inserted into these peptides wothout affecting their secondry structure. Co-oligomethionines. The effect of a glycyl residue are generally less ordered than the analogous homo-oligomethionines. The effect of a glycl residue on the structure of the longer oligopeptides depends on its position in the chain. When inserted in the center of a hexamer or heptamer, the single glycyl residue destabilizes the ordered secondry structures in solution. Finally, evidence is presented that the CD patterns observed for various pentamers and hexamers are consistent with some order at these chain lenghts.  相似文献   

12.
E Peggion  S Mammi  M Palumbo  L Moroder  E Wünsch 《Biopolymers》1983,22(11):2443-2457
The interactions of Des-Trp1-Nle12-minigastrin I (Nle11-HG-13) and Nle15-little gastrin I (Nle15-HG-17) with calcium ions have been investigated in water and in trifluoroethanol solution using uv and CD absorption techniques. Both hormones strongly interact with Ca2+ in the organic medium. In the case of Nle11-HG-13, the near-uv chiroptical properties (dominated by the transitions of the Trp residue in the C-terminal tetrapeptide sequence) indicate that three metal ions per mole of hormone are involved in the binding process. From the different response of near-uv and far-uv CD properties to the addition of calcium and from the change of the CD spectra in the aromatic absorption region, it is concluded that the biologically important C-terminal sequence is directly involved in the interaction with calcium. Elongation of the peptide chain from Nle11-HG-13 to Nle15-HG-17 (Nle15-little gastrin I) does not provide any additional binding site for calcium ions. The change of the CD properties in the near- and far-uv indicates that three metal ions per mole of hormone are involved in the binding process. The dichroic absorption in the aromatic region indicates that only one of the two Trp residues of the little gastrin analog is sensitive to the presence of calcium. On the assumption that the variation of the CD properties is proportional to the extent of calcium binding, the binding constants K1, K2, and K3 have been estimated roughly. Two similar sets of binding constants have been found, with K1 ≥ 106M?1 and K3 of the order of 105M?1, indicating similar binding sites in the two hormones with high affinity for calcium ions.  相似文献   

13.
The 1H-nmr spectra of co-oligopeptides of tryptophan and glycine with structure H-Gly-Trp-(Gly)n-Trp-Gly-OH (n = 0–2) and those of several di- and tripeptides have been recorded at 360 MHz with CD3OD solutions containing 0.1N NaOD. The assignment of resonance signals was generally possible by comparing the spectra of structurally related peptides with each other. In order to solve the remaining ambiguities in the assignment, H-(αL,βS)(α,β-d2)Trp-OH, H-Trp-(αL,βS)(α,β-d2)Trp-OH, and H-Trp-(δ12232-d5)Trp-OH have been prepared and their spectra compared with those of the undeuterated compounds. The distribution of rotamers around the χ1 and (in two cases) χ2 torsion angles of the side chains has been obtained from the vicinal coupling constants 3J and from the long-range coupling constants 4J. These data and an analysis of the chemical shifts of the Gly-Cα protons suggest that the orientation of the aromatic side chain is influenced by the following order of decreasing interaction with the functional groups at N- and C-side: -NH2 > –NHCO– > –CONH–> –COO?. This rule does not hold for the second Trp residue of di- and tripeptides containing the -Trp-Trp- sequence, which has tentatively been attributed to steric effects.  相似文献   

14.
The conformation of (Pro-Gly-Phe)n in trifluoroethanol was investigated using CD, nmr and ir techniques. After making appropriate correction for the contribution of the phenylalanine chromophore to the observed CD spectra of the polytripeptide at several temperatures, it is found that (Pro-Gly-Phe)n can exist in a partially triple-helical conformation in this solvent a t low temperatures. The nmr and ir data support this conclusion. In conjunction with recent theoretical sutdies, our data offer an explanation for the preferential occurrence of the Phe residue in position 2 of the tripeptide sequence Gly-R2-R3, in collagen.  相似文献   

15.
Conformation of αs-casein and its association were investigated from behaviors of tyrosyl and tryptophyl residues and hydrophobic sites. The chromophoric residues and ANS binding sites were buried into a region inaccessible to solvent with increasing concentration of αs-casein. It is considered that the association of αs-casein with concentration is proceeded by the hydrophobic sites to be able to bind ANS and the hydrophobic segments in which tyrosyl and tryptophyl residues exist. Below 0.04% of αs-casein, αs-casein exists in the monomer state and 80% of tyrosyl and tryptophyl residues are accessible to aqueous solvent. The hydro-phobic sites of αs-casein may be exposed to solvent in the monomer state.  相似文献   

16.
The properties relevant to nonradiative energy transfer have been computed in the unperturbed chain model for oligopeptides composed of from 4 to 21 residues of the formula Tyr-(Ala)n-Tyr and Trp-(X)n-Tyr, X being either Ala or Gly. A Monte Carlo method has been used for the generation of the chains. The relation between the distribution functions of the distances between the luminophores and the various properties in energy transfer has been examined for chains of different lengths and compositions. The averge of the orientation factor κ2 has been computed as a functions of chain length both for molecules in a randomly coiled state and for molecules with backbones in a well-defined three-dimensional structure. The various averaging regimes of energy-transfer efficiency and of fluorescence decay are compared. Theoretical curves relating experimental efficiencies to the mean distance between the luminophores are proposed.  相似文献   

17.
M Goodman  F Naider  C Toniolo 《Biopolymers》1971,10(9):1719-1730
A conformational analysis was carried out on a series of L -isoleucine oligomers having the general formula BOC-(Ileu)n-OMe (n = 2–8). These oligopeptides were examined in trifluoroethanol, trifluoroethanol-acid and mixed organic-water media. The results indicate that these oligomers form β-conformations beginning at the heptamer. The stability of the β-conformations was found to be greater than those formed by oligopeptides derived from L -alanine.  相似文献   

18.
High-resolution solid-state 13C-nmr spectra of two series of fully protected oligopeptides, Z-(Aib)n-OMe (n = 3?8) and Z-(Aib)n-L-Leu-(Aib)2-OMe (n = 0?5), were recorded to gain insight into main-chain length dependence for 310-helix formation. We found that all the oligopeptides examined adopt an incipient or a fully developed 310-helical structure, as judged from the characteristic splitting of the Cβ signals as well as the conformation-dependent displacements of the Cα and C?O peaks.  相似文献   

19.
Vibrational CD (VCD) spectra of a series of blocked linear, alternating D - and L -proline containing oligopeptides, dissolved in D2O and in CDCl3. are reported. For the Boc-LDL -Pro3 to Boc-DLDLDLDL-Pro8 oligomers. The VCD spectra in the amide I band is a positive couplet, opposite in sense to that obtained for (L -Pro)n oligomers. While this admits the possibility of their favoring a right-handed helical chain conformation, the amide I ir spectra for these dl oligomers in D2O indicate a mixed, apparently alternate, cis-trans conformation that prevents a simple conclusion. Their VCD in D2O evidence no narrowing and has a progressive loss in intensity (measured as Δ /A,) with an increase in chain length. In CDCl3a similar pattern of positive VCD couplets decreasing in intensity with length was seen, but their spectra are narrower. Their electronic CD (ECD) in the uv, also indicates a loss in intensity with increasing length. Oligomers with odd or even numbers of Pro residues have different ECD patterns, indicating that those spectra are strongly influenced by local contributions arising in the N-terminal groups. The VCD arises from dipolar and vibrational coupling of the amides in the helical structure. All the spectra are consistent with the chiral end groups leading to formation of an excess of one helical handedness. With an increase in length, the influence of this selectiveness is less and the overall CD measured decreases. © 1995 John Wiley & Sons, Inc.  相似文献   

20.
The ability of oligodesoxyribonucleotides of various chain lengths to form complexes has been compared with that of oligoribonucleotides. Four series of oligonucleotidcs were prepared and investigated, i.e., dCn at acid pH versus rCn, dAn and dTn versus. rAn and rUn at neutral pH. The results indicate that in dilute solution, the formation of complexes is greatly facilitated in the case of desoxyoligomers and occurs for shorter oligomere than in the corresponding ribooligomers. The spectrophotometric titration of deoxyribooligo C indicates the appearance of two pK values in the 4–5 pH region characteristic of the double-stranded form, which occurs for much shorter dCn than rCn. The circular dichroism (CD.) spectra of deoxycytidylies in dilute solution starting from the trimer are conservative, characteristic of the double-stranded helical form of poly C at acid pH. In contrast, the CD spectra of a series of corresponding ribo Cn, under identical conditions is of nonconservative character similar to that of the single-stranded form of poly C at neutral pH, but differs in the band position. This spectrum is called intermediate. Only at higher concentrations of oligonucleotidcs (i.e., 10?3Minstead of 10?4M) does the circular dichroism spectrum of longer ribocytidylics assume conservative character. Thermal denaturation of deoxycytidylces at acid pH are strongly dependent on chain length and concentration, its one would expect for a cooperative helix-coil transition. The circular dichroism spectra measured at different temperatures shows one isosbestic point. In dilute solution, the standard-state enthalpy change found was 5–6 kcal/mole for higher oligomers (dC7). These properties are all in agreement with a structural transition from the d-Cn double-stranded form to a coil for n > 3. Studies of dAn and dTn in solutions of high ionic strength at low temperature indicate that complex formation occurs already at the level of trimer and for high oligomers. Under identical conditions a complex between rAn and rUn is detected only for oligomers longer than the hexamer. The nature of the “intermediate” form of oligoribo C at acid pH and low temperature was investigated by sedimentation and circular dichroism. A model of rCn is proposed of linear molecules which are partially double-stranded and partially single-stranded, which probably are slowly rearranged by “slippage” into a regular-double-stranded helical form.  相似文献   

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