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Query: HUMANGGP:003721 (Poly)
 11,742 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The interaction of a number of potentially complementary monomers with poly(A) has been investigated by equilibrium dialysis, optical rotatory dispersion and ultraviolet absorption measurements. Experiments were conducted at pH 7.0, 0.15 M Na+, where poly(A) exists as a random coil with some degree of base-stacking, and at pH 6.0, 0.15 M Na+, where poly(A) adopts the protonated double-helical acid form structure below 15 degrees C. Binding isotherms show that, at 3.5 degrees C, poly(A) forms a 1 : 1 complex with xanthine at pH 6, and a 2:1 complex at pH 7, while oxoformycin forms a 1:1 complex with poly(A) at both pH 6 and pH 7. Poly(A) forms a complex, tentatively assigned 1:1 stoichiometry, with 8-azaxanthine at pH 6, but no complexing occurs at pH 7. The complexes have been characterized by their optical rotatory dispersion and ultraviolet spectra, their thermal stabilities, and their rates of formation at low temperature. All the complexes are laevorotatory at long wavelengths (greater than 300 nm) and unplex formation at low temperature is a slow process requiring many hours for completion. The complexes of poly(A) with 3-methylxanthine have been reinvestigated and shown to undergo normal helix-coil transitions; the anomalous melting behaviour noted previously [Biopolymers, 10, 21 -- 33 (1971)] has been explained. From a comparison of optical rotatory dispersion spectra, it is concluded that the poly(A) with 3-methylxanthine have similar structures, which are quite different from the structures of the corresponding complexes with 7-methylxanthine. The structures and properties of the poly(A) - monomer complexes are discussed, and compared with those of other polynucleotide - monomer complexes. No significant interaction was observed between poly(A) and hypoxanthine, allopurinol, 6,8-dihydroxypurine, 1-methylxanthine, 9-methylxanthine, theophylline, theobromine or 3,9-dimethylxanthine.
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PMID:Complexes of poly(adenylic acid) with complementary monomers. 124 84

The adjacent GN7-M-GN7 cross-linking and adjacent G-M-G sandwich-complex models for DNA metal ion binding were evaluated both with native DNAs differing in GC content as well as with the synthetic polymers poly [(dGdC)]2, poly[(dAdT)]2, and poly[(dAdC)(dGdT)]. The effect of Zn2+ was studied in depth, and limited studies were also performed with Co2+ and Mg2+. The results were compared to the extensive information available on Cu2+ binding to native DNAs and poly[(dAdT)]2. At high ratios of metal/base (R), Zn2+ caused all native DNAs to denature with the same melting temperature Tm, approximately 61 degrees C. A similar pattern was reported previously for Cu2+, but the typical Tm was approximately 35 degrees C. The extent of renaturation on cooling DNAs denatured in the presence of Zn2+ increased with GC content, as reported previously for Cu2+. These results, together with previously reported similarities, strongly indicate that the DNA binding characteristics of the two cations are similar. By comparison of the Tm values and hyperchromicity changes monitored at 260 and 282 nm, it is clear that, during thermal denaturation in the presence of Zn2+, both AT and GC regions were denatured, even at high R. The Tm vs R profile for the native DNAs was typical. The rise at low R and subsequent decrease at high R were inversely and directly related, respectively, to GC content. Except for poly[(dAdT)]2, where Tm increased with R, the other synthetic polymers exhibited the increase/decrease pattern. Poly[(dAdC)(dGdT)] gave a Tm value at high R of 54 degrees C. In the absence of Zn2+, this polymer exhibited little hypochromicity on cooling of denatured polymer. However, in the presence of Zn2+, nearly complete hypochromicity was observed, although the midpoint of the cooling curve was lower than the Tm value by approximately 15 degrees C at R = 10. These characteristics were similar to those with native DNAs, although viscosity and CD studies suggested that the "renatured" polymer was not identical to the unheated polymer. Furthermore, addition of Zn2+ after denaturation nearly completely reversed the absorption increase. This finding contrasts with those for native DNAs, where the Zn2+ must be present during denaturation in order to reverse the absorption increase nearly completely on cooling. With some caveats, poly[(dAdC)(dGdT)] appears to be a good model for native DNAs since its properties, including CD and uv changes on addition of Zn2+ to premelted and melted polymer, parallel those of the native polymers.(ABSTRACT TRUNCATED AT 400 WORDS)
Biopolymers 1991 Jan
PMID:Zinc ion-DNA polymer interactions. 202 84

The chemical and biological properties of collagen are altered by the biosynthetic substitution of the L-azetidine-2-carboxylic acid(Aze) residue in the place of proline. The reasons for this alteration have been studied by means of conformational energy computations on single- and triple-stranded structures formed by poly(Gly-X-Y) poly(tripeptide)s, where X and Y can be Pro or Aze. The most stable triple helix formed by Poly(Gly-Pro-Aze) is collagen-like, but all low-energy triple helices that can be formed by poly(Gly-Aze-Pro) and poly(Gly-Aze-Aze) are very different from collagen. Thus, the regular substitution of Aze for Pro in position X is not compatible with the collagen structure. In the absence of solvent effects, all of these triple helices are stable, relative to the statistical coil, but the substitutions reduce the stability of the collagen-like triple helix, as compared with poly(Gly-Pro-Pro).
Biopolymers 1990
PMID:The effect of the L-azetidine-2-carboxylic acid residue on protein conformation. III. Collagen-like poly(tripeptide)s. 209 25

Poly(L-lysine) bound to phosphatidylglycerol or phosphatidic acid bilayers was submitted to hydrostatic pressure in a diamond anvil cell to investigate whether the lipidic surfaces can protect the polypeptide against pressure-induced conformational transformations. The amide I region of the infrared spectrum of dimyristoylphosphatidic acid bound polylysine shows that most of the polypeptide retains its beta-sheet structure up to 19 kbar, while it is known to convert entirely to alpha-helix at approximately 2 kbar in the absence of the lipid [Carrier, D., Mantsch, H.H., & Wong, P.T.T. (1989) Biopolymers (in press)]. The simultaneous binding of the polypeptidic molecules to two opposing bilayers appears to be required in order to preserve the beta-sheet structure at pressures over approximately 9 kbar: a small proportion of the polypeptide, most likely the molecules at the surface of the aggregated bilayers, was found to convert to unordered and eventually to alpha-helical conformations in the pressure range 9-19 kbar. The decrease from 1612 to 1606 cm-1 of the frequency of the major beta-sheet component of the infrared amide I band as the pressure is raised to 6 kbar indicates a strengthening of the interchain hydrogen bonds. The high-pressure infrared spectra of polylysine bound to dimyristoyl- and dipalmitoylphosphatidylglycerol show that the polypeptide remains alpha-helical up to approximately 12 kbar, though the changes in the bandshape indicate an increase in hydrogen bond strength. The formation of a small amount of beta-sheet was observed during decompression and is attributed to the effect of dehydration on the polypeptidic molecules located at the surface of the aggregates.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Protective effect of lipidic surfaces against pressure-induced conformational changes of poly(L-lysine). 232 44

The inclination angle between the base normal and the helix axis, and the axes around which the bases incline, are measured for ribo-GC polymers in buffer by using flow linear dichroism (LD), and compared to measurements for deoxyribo-GC polymers in buffer and under dehydrating conditions. A new method is designed to synthesize poly(rGrC)-poly(rGrC), which is not available commercially, in large quantities. The LD of this RNA reveals inclination angles that are similar to the B-form DNA in buffer, although the axes are different. The CD of poly(dGdC)-poly(dGdC) under the dehydrating conditions is similar to poly(rGrC)-poly(rGrC), indicating it is in the A form, and the LD gives larger inclination angles than either the B form or the corresponding RNA. Poly(dG)-poly(dC) is in the A form in buffer. Comparison among poly(rG)-poly(rC) in buffer, and poly(dG)-poly(dC) in buffer under dehydrating conditions, reveals similar inclination angles and axes, although the LD shows that the DNA has the largest inclination angles. Except for poly(rGrC)-poly(rGrC), which has a unique reduced dichroism, all the axes for G are similar, as are the axes for C.
Biopolymers 1995 Sep
PMID:Comparison of base inclination of ribo-GC and deoxyribo-GC polymers, and synthesis of poly(rGrC)-poly(rGrC). 754 45

Poly(beta-l-aspartate)s are known to take up helical conformations reminiscent of the alpha-helix of polypeptides. The isobutyl, n-butyl, and 2-methoxyethyl esters have been examined by polarized ir spectroscopy in order to discriminate between the left (1L) and right (2R)-handed conformations, which are known to be compatible with the 13/4-helix adopted by these polyamides when crystallized in the hexagonal form. Dichroic ratios obtained from samples stretched in poly(ethylene oxide) together with orientation measurements made by x-ray diffraction were used to estimate the transition moment directions of amide A, I, and II bands with respect to the fiber axis. These were compared to those calculated by modeling simulations to conclude that the right-handed conformation consisting of 14-membered hydrogen-bonded rings is the correct model for the 13/4-helix. These results give definite support to earlier molecular mechanics calculations, which had shown that the 2R model is energetically favored over the 1L by about 2.5 kcal/(mol residue).
Biopolymers 1995 Sep
PMID:Conformational analysis of helical poly(beta-L-aspartate)s by IR dichroism. 766 14

We describe the synthesis of several polyamides that retain the secondary structure of proteins and contain derivatizable side chains. The derivatizable side chain allows for further reaction of the polymer chain (e.g., chain cross-linking or addition of pendant groups). Polymers of alpha-amino acids containing a terminal unsaturated bond on the side chain have been synthesized. Poly-L-pentenyl glycine, poly-L-propargyl glycine, and poly-L-allyl glycine were synthesized chemically via Leuchs' anhydrides and enzymatically using subtilisin Carlsberg. Poly-L-propargyl glycine and poly-D,L-allyl glycine folded into the beta-sheet configuration whereas poly-L-pentenyl glycine assumed a helical conformation. The secondary structure of poly-L-allyl glycine and poly-D,L-pentenylglycine could not be determined conclusively. Comparison of properties between the polymers obtained chemically and enzymatically is provided.
Biopolymers 1995 May
PMID:Synthesis and characterization of polyamides containing unnatural amino acids. 776 20

Poly(Lys-Tyr-Tyr-Lys) was synthesized by polycondensation of the tetrapeptide unit using paranitrophenyl esters. The conformation of poly(Lys-Tyr-Tyr-Lys) is very dependent on its environment. CD spectra in bulk are difficult to interpret owing to the contribution of Tyr residues, but from ir spectra it seems that poly(Lys-Tyr-Tyr-Lys) adopts preferentially an unordered conformation in water. Addition of salts induces a partial transition to a beta structure. The behavior is different at interfaces. When poly(Lys-Tyr-Tyr-Lys) is spread as a film on a water subphase, the shape of the compression isotherm curves is compatible with a stacking of two beta-sheets. On a KCl subphase, the polymer film is more expanded and more compressible, and the isotherm curve resembles that of a polymer in a random conformation. The analysis by CD and ir spectroscopy of transferred monolayers using the Langmuir-Blodgett technique allowed us to confirm and make these data more precise: on a water subphase the spectra are those of an antiparallel beta structure. At the interface of a saline solution the spectra are compatible with a mixture of random coil (largely) and a small content of beta structures.
Biopolymers 1995 Jun
PMID:Synthesis and interfacial behavior of poly(Lys-Tyr-Tyr-Lys). 776 28

The clavicepamines are lysine-rich basic proteins isolated from saprophytic culture of ergot (Claviceps purpurea), having human pharmacological importance. Based on structure determinations, it was demonstrated that the epsilon-lysine (poly)peptides are the fundamental structural units of clavicepamines. To study the relationship between chemical structure and biological effect, solution and solid-phase synthesis of lysine isopeptides were performed. Poly-epsilon-lysines were synthesized with polycondensation via application of p-nitrophenylester temporarily protecting groups together with simultaneous activation. The biological investigations of poly-epsilon-lysines showed a cell-proliferation retarding effect, so they inhibit growth of some animal tumors, practically without toxic side effects.
Biopolymers 1997 Sep
PMID:Structure determination and synthesis of lysine isopeptides influencing on cell proliferation. 927 24

Poly(Leu-Lys-Lys-Leu) and poly(Leu-Lys) are sequential amphiphilic peptide isomers that adopt respectively an alpha-helical conformation and a beta-sheet structure in saline solutions and at the air/water interface. The surface active properties of LKKL and LK sequential isopeptides containing 16, 20, and n residues have been compared in order to evaluate the contributions of the alpha-helical and beta-sheet conformations. Both have a natural tendency to spread at the surface of a saline solution and the values of the equilibrium spreading pressure pi(e) lie in the same range. When dissolved in a saline solution, alpha-helical peptides diffuse faster and adsorb faster at the interface than the beta-sheet isomers. From the compression isotherms of LKKL and LK peptide monolayers it is possible to extract parameters that characterize the behavior of alpha-helical and beta-sheet conformations: beta-sheet peptide monolayers are more stable and less compressible than the monolayers formed with the alpha-helical isomers. The LK peptides differ also by their high degree of self-association at the air/water interface. Copyright 1999 John Wiley & Sons, Inc.
Biopolymers 1999 Apr 15
PMID:Surface active properties of amphiphilic sequential isopeptides: Comparison between alpha-helical and beta-sheet conformations. 1118 48


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