Proton magnetic relaxation in solid poly(L-alanine), poly(L-leucine), poly(L-valine), and polyglycine

Molecular motion in solid poly(L -alanine), Poly(L -leucine), poly(L -valine), and polyglycine has been investigated through measurement of the portion spin-lattice relaxation time at 30 and 60 MHz between 110 and 350°K. Rapid random reoriention of sied-chain methyl groups provides the dominent source of relaxation in the first three; activation energies are 10.5 ± 1 1, 8.5 ± 1 kJ/mol, respectively, significantly lower than in the monomeric crystals. Relaxation times in poyglycine are two orders of magnitude longer than in the monomeric crystals. Relaxation times in polyglycine, significantly lower than in the monomeric crystals. Relaxation times in polyglycine are two orders of magnitude longer and are attributed mainly to segmental motions of the polymer chains. Evidence of nonexponential recovery of nuclear magnetization was encountered in the first three homopolyamino acids but not in polylycine, and was attributed to the correlated time to characterize these motions gave quite good agreement with the data; some improvement was obtained for two polymers using a Cole-Davidson distribution of correlation times. For biopolymers using a Cole-Davidson distribution of correlation times. For biopolymers generally it is concluded that rapid methyl group reorientation is a common dynamical feature and an important source of nuclear magnetic relaxation.     

A study of conformational stability of poly(L-alanine), poly(L-valine), and poly(L-alanine)/poly(L-valine) blends in the solid state by (13)C cross-polarization/magic angle spinning NMR

13C cross-polarization/magic angle spinning (CP/MAS) NMR and (1)H T(1rho) experiments of poly(L-alanine) (PLA), poly(L-valine) (PLV), and PLA/PLV blends have been carried out in order to elucidate the conformational stability of the polypeptides in the solid state. These were prepared by adding a trifluoroacetic acid (TFA) solution of the polymer with a 2.0 wt/wt % of sulfuric acid (H(2)SO(4)) to alkaline water. From these experimental results, it is clarified that the conformations of PLA and PLV in their blends are strongly influenced by intermolecular hydrogen-bonding interactions that cause their miscibility at the molecular level.     

Heat capacities of solid poly(amino acid)s. II. The remaining polymers

In the first paper heat capacities C_p, of polyglycine, poly(L -alanine), and poly (L -valine) were analyzed using approximate group vibrations and fitting the C_p contributions of the skeletal vibrations to a two-parameter Tarasov function. In this second paper all other poly (amino acid) s are similarly analyzed. Heat capacities were measured by differential scanning calorimetry in the temperature range of 230–390 K for poly(L -leucine), poly(L -serine), poly (sodium-L -aspartate), poly(sodium-L -glutamate), poly(L -asparagine), poly(L -phenylalanine), poly(L -tyrosine), poly(L -methionine), poly (L -tryptophane), poly(L -proline), poly(L -lysine · HBr), poly(L -histidine), poly(L -histidine- HCl), and poly(L -arginine · HCl). Good agreement exists between experiment and calculation. Predictions of heat capacities were made for all not-measured poly (amino acid) s. Enthalpies, entropies, and Gibbs functions for the solid state have been derived. © 1993 John Wiley & Sons, Inc.     

Laser-Raman spectroscopy of biomolecules. XI. Conformational study of poly(L-valine) and copolymers of L-valine and L-alanine

Raman spectroscopic studies have been carried out on polymers of L -valine ranging in degree of polymerization (DP) from 2 to 930. The spectrum of the hexapeptide (DP = 6) is closely similar over the entire range 40–1750 cm^?1 to those of polymers with much higher DP, and the structure is clearly shown to be that of the antiparallel pleated sheet (β-structure) by the amide I and III frequencies. The formation of a little α-helical structure occurs in polymers with DP above 500, although the amount does not appear to be a linear function of DP. The α-helical structure is unstable and readily destroyed in samples cast from trifluoroacetic acid solution. It is stabilized by the incorporation of L -alanine, a strong helix-former; polymers of the latter may in turn be forced into a α-structure in copolymers sufficiently rich in L -valine.     

Structure of poly (I).poly (A).poly (I)

The molecular structure of poly (I).poly (A).poly (I) has been determined and refined using the continuous intensity data on layer lines in the x-ray diffraction pattern obtained from an oriented fiber of this polymorphic RNA complex. The polymer forms a 12-fold right-handed triple-helix of pitch 39.7A and each base-triplet is stabilized by quasi Crick-Watson-Hoogsteen hydrogen bonds. The ribose rings in all the three strands have C3'-endo conformations. The final R-value for this best structure is 0.24 and the x-ray fit is significantly superior to all the alternative structures where the different chains might have different furanose conformations. This all-purine triple-helix, counter-intuitively, has a diameter roughly 3A shorter than that of DNA and RNA triple-helices containing a homopurine and two complementary homopyrimidine strands. Its compact, grooveless cylindrical shape is consistent with the lack of lateral organization.     

Alkylated poly(amino acids). I. Conformational properties of poly(Nε-trimethyl-L-lysine) and poly(Nδ-trimethyl-L-ornithine)

Poly(N^ε-trimethyl-L -lysine), [Lys(Me₃)]_n, and poly(N^δ-trimethyl-L -ornithine), [Orn(Me₃)]_n, in sodium dodecylsulfate do not assume the β-structure or α-helix, respectively, of their parent polymers. In 0.5M Ca(ClO₄)₂ both [Lys(Me₃)]_n and [Orn(Me₃)]_n are aggregated and display CD spectra indicative of a regular, perhaps helical, structure. For [Lys]_n and [Lys(Me₃)]_n, the T₁ of the α-hydrogens are 0.379 and 0.230 sec, respectively, indicating greater rigidity for [Lys(Me₃)]_n. The CD spectrum of [Lys(Me₃)]_n at pH 8 is more heat resistant than that of [Lys]_n. It is suggested that apolar interactions are more important in the methylated polymers than in the parent polymers.     

Low-frequency dynamics of solid poly(L-alanine) from Raman spectroscopy

Raman modes from amorphous α-helical poly(L -alanine) in the low-frequency region < 150 cm^?1 have been observed and assignments and values compared with mode-analysis calculations. The temperature dependence of the complete Raman spectrum of α-poly(L -Ala) is also reported.     

A study of conformational stability of polyglycine and poly(L-alanine), and polyglycine/poly(L-alanine) blends in the solid state by (13)C cross-polarization/magic angle spinning NMR

13C Cross-Polarization/Magic Angle Spinning nmr and T(1rhoH) experiments of polyglycine (PG), poly(L-alanine) (PLA), and PG/PLA blends prepared from dichloroacetic acid solution have been carried out, in order to elucidate the conformational stability of these polypeptides in the solid state. From these experimental results, it was clarified that the conformations of PG and PLA in their blends are strongly influenced by intermolecular hydrogen-bonding interactions that cause their miscibility at the molecular level.     

Recognition of polynucleotides by antibodies to poly(I), poly(C).

The binding of anti poly(I). poly (C) Fab fragments to double or triple stranded polynucletides has been studied by fluorescence. Association constants were deduced from competition experiments. The comparison of the association constants leads to the conclusion that several atoms of the base residues do not interact with the amino acid residues of the binding site of Fab fragment while the hydroxyl groups of furanose rings interact. These results suggest that the Fab fragments do not bind to the major groove of the double stranded polynucleotides. An interaction between the C(2)O group of pyrimidine residues and Fab fragments cannot be excluded. Circular dichroism of poly(I). poly(C) or poly(I). poly(br5C)-Fab fragments complexes are very different from the circular dichroism of free polynucleotides which suggests a deformation of the polynucleotides bound to the Fab fragments.     

Ferric complexes of acetoacetyl derivatives of poly(L-lysine), poly(L-ornithine), and poly(L-diaminobutyric acid). I. Preparation and absorption properties in solution

Poly(N^ε-acetoacetyl-L -lysine), poly(N^δ-acetoacetyl-L -ornithine) and poly(N^γ-acetoacetyl-L -diaminobutyric acid) form colored complexes with ferric ions in water/dioxane solutions. These complexes are soluble at pH values lower than 2.8 and show their maximum absorption at 257 nm in the uv and at 478 nm in the visible region; whereas the ferric complex of the model compound n-hexylacetoacetamide exhibits absorptions centered at 258 and 536 nm, respectively. It is shown that in the complex of the model compound one metal ion is bound per acetoacetamide group, while in the complexes of the three polymers two β-ketoamides side chains are bound per ferric ion under the same solvent, pH, concentration, and ionic strength conditions. The binding constants of ferric ions to the three polymers, and the formation constant of the ferric complex of the model compound are also evaluated.     

Dissociation of double-stranded poly(I) . poly(C) by cis-diammine-dichloro-Pt(II).

The covalent binding of cis-Pt(NH3)2Cl2 on the double stranded poly(I) . poly(C) induced an irreversible dissociation of the two strands. This dissociation was evidenced mainly by poly(I)-Agarose affinity chromatography which allowed to recover free strands of cis-Pt(NH3)2Cl2-poly(I) from a cis-Pt(NH3)2Cl2-poly(I) . poly(C) complex, by density equilibrium centrifugation where free poly(C) could be isolated, and by acid titrations of the metal-poly(I) . poly(C) complexes. The separation of the two strands of the polyribonucleotide upon cis-Pt(NH3)2Cl2 fixation was shown not to exceed 90--95%. A dissociation curve of the polynucleotide double helix as a function of the amount of bound cis-Pt(NH3)2Cl2 was determined and was shown to be of a characteristic cooperative effect. The fixation of the paltinum compound to poly(I) . poly(C) seemed also to be cooperative.     

Vibrational analysis of peptides,polypeptides, and proteins. I. Polyglycine I

A force field has been refined for the antiparallel chain-rippled sheet structure of polyglycine I. Transition dipole coupling and hydrogen bonding are explicitly taken into account. Amide I and amide II mode splittings are well accounted for, the latter also providing a quantitative explanation of the amide A and amide B mode frequencies and intensities. In addition to predicting other features of the vibrational spectrum of polyglycine I, this force field is completely transferable to other β polypeptides, even though these have the antiparallel chainpleated sheet structure.     

Interaction of amino acids with silver(I) ions.

The reactivity of silver(I) ions towards twenty amino acids has been studied in aqueous unbuffered solutions using an ion-selective electrode as a highly sensitive monitor. Contrary to general belief, silver ions are not completely specific for cysteine, but also react with lysine, arginine, methionine and, to a minor extent, cystine. Nevertheless the interaction with all of these species except cysteine is too weak to affect significantly the determination of thiol in proteins by the customary argentometric titration method. The possible origin of errors arising in such titrations is discussed.     

Proton-NMR study of the interaction of trans-dichloro-diamine-platinum(II) with poly(I) and poly(I).poly(C)

The fixation of trans-(NH₃)₂Cl₂ Pt(II) to poly(I)·poly(C) at low r_b (< 0.05) leads to the formation of two complexed species. The major species (ca. 82% of bound platinum) involves coordination of platinum to a single hypoxanthine base, while the other species involves coordination of two hypoxanthine bases, which are either far apart on the same strand or on separate poly(I) strands, to the platinum. These same two species are found after reaction with poly(I), as are two other species throughout the entire r_b range studied (r_b = 0–0.30). The latter two species are assigned to trans-Pt bound to two bases on a poly(I) strand with (a) one or (b) two free bases between the two bound bases. These two species, (a) and (b), account for ca. 35% of the bound platinum, although the 1:1 species remains dominant (ca. 55%). These two additional species are observed at high r_b (>0.075) after reaction with poly(I)·poly(C) but as very minor species. They are formed by reaction with melted poly(I) loops. Also at high r_b, we have observed a shifted cytidine H⁵ resonance arising from interaction of trans-Pt with a melted loop of poly(C). Most probably, this arises from an intramolecular poly(I) to poly(C) crosslink. Results from the reaction of trans-Pt with poly(C) are presented for comparison.     

Biosynthesis of poly(3-hydroxyalkanoate) from amino acids

It was found that an optically active copolyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), denoted as P(3HB-co-3HV), is synthesized by Alcaligenes eutrophus H16 from several amino acids under various fermentation conditions. The optimum condition for the biosynthesis from one amino acid, threonine, was investigated and its biosynthetic pathway was discussed on the basis of the relation between the fermentation condition and the co-monomer composition of the produced polyesters.