Helix to coil transition in poly-L-amino acids. II. N.M.R. study of model compounds and Poly-γ-benzyl-L-glutamate

1969 ◽  
Vol 22 (2) ◽  
pp. 357 ◽  
Author(s):  
JH Bradbury ◽  
MD Fenn
Keyword(s):  
Amino Acids ◽  
Molecular Weight ◽  
Magnetic Resonance ◽  
Amide Group ◽  
Dichloroacetic Acid ◽  
Model Systems ◽  
Optical Rotatory Dispersion ◽  
Random Coil ◽  
Low Molecular Weight ◽  
Coil Transition

The proton magnetic resonance spectroscopy of simple amides and poly-L- amino acids has been investigated with particular reference to the question of charging of the amide group in strong acids. It is found that the downfield chemical shift of the α-CH resonance of poly-γ- benzyl-L-glutamate (PBG) which accompanies the helix to coil transition can be conveniently divided into two parts on the basis of experiments with model systems. The first is due to the collapse of the helix to an uncharged random coil and the second represents the charging of the amide groups of the random coil. For PBG samples of low molecular weight, two α-CH resonances are observed due to residues in helical (uncharged) and random-coil (charged) forms. The rate of exchange between them is of the order of 400 sec-1. The proton resonances of the NH proton, COOH proton of the acid, and α-CH proton of dichloroacetic acid (DCA) are shown to be less useful than the α-CH proton. A critical evaluation has been made of all the evidence relevant to the charging of the amide group of polypeptides in mixtures of non-interacting solvents and organic acids e.g. trifluoroacetic acid (TFA) and DCA. It is concluded that viscosity, infrared, dielectric constant, electric birefringence, and conductivity studies give overwhelming support to the concept of charging. Nuclear magnetic resonance, circular dichroism, and optical rotatory dispersion are less sensitive indicators of small amounts of charging, and hence studies should be made with samples of low molecular weight (where there is a greater fractional degree of charging). Such studies made here by n.m.r. methods give strong support for charging. The features of the flexible helix model first proposed in Part I are delineated. It consists of helical segments separated by short, charged random-coil breaks at both ends and in the interior of the molecule. Although elaborated in some detail for the case of PBG, it is likely to occur quite generally for those polypeptides which are soluble in organic solvents and undergo the helix to coil transition.

Nuclear magnetic resonance spectroscopy of denatured proteins

1969 ◽  
Vol 22 (5) ◽  
pp. 1083 ◽  
Author(s):  
JH Bradbury ◽  
NLR King
Keyword(s):  
Molecular Weight ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Trifluoroacetic Acid ◽  
Guanidine Hydrochloride ◽  
Dichloroacetic Acid ◽  
Random Coil ◽  
Resonance Spectroscopy ◽  
Line Broadening ◽  
Line Widths

The proton magnetic resonance spectroscopy of 11 proteins (molecular weight range 5700-650000) has been investigated in five denaturing solvents, viz., trifluoroacetic acid-d, formic acid, dichloroacetic acid, 6M guanidine hydrochloride in D2O, and 8M urea in D2O. The chemical shifts, line-widths, and intensities of the resonances have been measured of the histidine C2 protons, the methionine SCH3 protons and methyl protons of leucine, isoleucine, and valine, the aromatic protons, and the α-CH protons. ��� It is found that, with some exceptions delineated below, the line- widths of the methyl resonances are constant for a particular solvent, independent of the molecular weight of the protein. This indicates that, in general, the proteins behave as random coil structures in these solvents, which confirms the conclusion reached by Tanford and co-workers1-4 for 6M guanidine hydrochloride. ��� However, methyl line broadening occurs in dichloroacetic acid for catalase and fibrinogen, in guanidine hydrochloride for insulin, and in urea for insulin and lysozyme. Furthermore, the C 2 histidine resonance is absent in dichloroacetic acid solutions of thyroglobulin, catalase, and fibrinogen; the SCH3 resonance is absent in myoglobin in trifluoroacetic acid-d and occurs as a doublet for trypsin in guanidine hydrochloride and in urea. A general line broadening of resonances indicates association and/or incomplete unfolding of molecules, whereas perturbations of only one particular resonance, as in the cases detailed above, are probably due to intramolecular non-covalent interactions which involve the perturbed group and another unspecified group in the protein. ��

Difunctional enols of N-protected amino acids as low molecular weight and novel inhibitors of HIV-1 protease.

1993 ◽  
Vol 3 (6) ◽  
pp. 1169-1174 ◽  
Author(s):  
Marc Vaillancourt ◽  
Benoit Vanasse ◽  
Eric Cohen ◽  
Gilles Sauv
Keyword(s):  
Amino Acids ◽  
Molecular Weight ◽  
Low Molecular Weight ◽  
Hiv 1

STUDIES ON THE ISOLATION AND NATURE OF THE 'TERREGENS FACTOR'

1954 ◽  
Vol 32 (1) ◽  
pp. 400-406 ◽  
Author(s):  
M. O. Burton ◽  
F. J. Sowden ◽  
A. G. Lochhead
Keyword(s):  
Amino Acids ◽  
Molecular Weight ◽  
Ferric Iron ◽  
Test Organism ◽  
The Other ◽  
Inorganic Salts ◽  
Low Molecular Weight ◽  
Straight Chain ◽  
Heat Stable ◽  
Growth Promoting

A procedure is described for the production and concentration of the 'terregens factor' (TF), a bacterial growth promoting substance synthesized by Arthrobacter pascens and essential for the growth of Arthrobacter terregens. From culture filtrates of A. pascens cultivated in a medium of inorganic salts and sucrose, concentrates of TF may be obtained that are active at 0.001 μgm. Per ml., heat stable and contain about 12.7% nitrogen. Acid hydrolysis yielded a number of amino acids, including glutamic acid, glycine, α–alanine, valine, leucine, proline, lysine, and arginine, as well as some unidentified compounds; however, TF does not appear to be a low molecular weight straight chain peptide.Although TF contains no iron, it combines readily with ferrous or ferric iron to form reddish-brown complexes with this metal. Activity for A. terregens is shown by certain iron containing complexes as hemin, coprogen, and ferrichrome. On the other hand none is shown by cytochrome or pulcherrimin; however, aspergillic acid, structurally related to the latter, possesses some growth promoting activity for the test organism.

Seasonal changes in the chemical composision of the red alga Hypnea musciformis

1973 ◽  
Vol 24 (3) ◽  
pp. 275
Author(s):  
AF Abdel ◽  
NM Abed ◽  
M Edrees
Keyword(s):  
Amino Acids ◽  
Molecular Weight ◽  
Chemical Composition ◽  
Seasonal Changes ◽  
Free Amino ◽  
Glucuronic Acid ◽  
Red Alga ◽  
Low Molecular Weight ◽  
Hypnea Musciformis ◽  
Algal Material

Seasonal changes were observed in the chemical composition of the marine red alga Hypnea musciformis. Lipids, cholesterol, and lanosterol were found as constituents of the algal material. No low-molecular weight carbohydrates were found except small amounts of mannitol. The algal hydrolysate was shown to contain galactose, glucose, and xylose in all seasons and was characterized by a high content of glucuronic acid and its lactone in February. Definite seasonal variations were found in the patterns of free amino acids and of amino acid compositions of proteins.

scholarly journals Pressure dependence of side chain 1H and 15N-chemical shifts in the model peptides Ac-Gly-Gly-Xxx-Ala-NH2

2020 ◽  
Vol 74 (8-9) ◽  
pp. 381-399
Author(s):  
Markus Beck Erlach ◽  
Joerg Koehler ◽  
Claudia E. Munte ◽  
Werner Kremer ◽  
Edson Crusca ◽  
...  
Keyword(s):  
Amino Acids ◽  
Pressure Dependence ◽  
Chemical Shifts ◽  
Model Systems ◽  
Random Coil ◽  
Nonlinear Dependence ◽  
Side Chain ◽  
Unfolded Proteins ◽  
Pressure Coefficients ◽  
Compression Effects

Abstract For interpreting the pressure induced shifts of resonance lines of folded as well as unfolded proteins the availability of data from well-defined model systems is indispensable. Here, we report the pressure dependence of 1H and 15N chemical shifts of the side chain atoms in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH2 (Xxx is one of the 20 canonical amino acids) measured at 800 MHz proton frequency. As observed earlier for other nuclei the chemical shifts of the side chain nuclei have a nonlinear dependence on pressure in the range from 0.1 to 200 MPa. The pressure response is described by a second degree polynomial with the pressure coefficients B1 and B2 that are dependent on the atom type and type of amino acid studied. A number of resonances could be assigned stereospecifically including the 1H and 15N resonances of the guanidine group of arginine. In addition, stereoselectively isotope labeled SAIL amino acids were used to support the stereochemical assignments. The random-coil pressure coefficients are also dependent on the neighbor in the sequence as an analysis of the data shows. For Hα and HN correction factors for different amino acids were derived. In addition, a simple correction of compression effects in thermodynamic analysis of structural transitions in proteins was derived on the basis of random-coil pressure coefficients.

Propriétés hydrodynamiques des conformations ordonnées et desordonnées du poly(γ-L-glutamate de benzyle): dimensions et flexibilité de la chaîne

1978 ◽  
Vol 56 (11) ◽  
pp. 1569-1574
Author(s):  
Nga Ho-Duc
Keyword(s):  
Quantitative Agreement ◽  
Dichloroacetic Acid ◽  
Random Coil ◽  
Hydrodynamic Properties ◽  
Molecular Weights ◽  
Coil Transition ◽  
Rigid Segment ◽  
Good Agreement ◽  
Stiff Chain

Theoretically we can determine the disordered or ordered structure of polypeptides and their dimensions in dilute solutions from hydrodynamic properties. We have presently a wealth of theories for random coil chains and a limited but sufficient number of theories for ordered chains for interpreting experimental results.Viscosity data for seven poly(γ-benzyl-L-glutamate) samples in 1,2-dichloroethane at 25 °C are analyzed and the length per monomeric residue (h) is calculated according to the equivalent ellipsoid approach. The degree of flexibility or rigidity is characterized by calculating Ns, the number of monomer units in a rigid segment or a Kuhn statistical segment; the determination of Ns is made by applying Yamakawa and Fujii's equation modified by Vitovskaya and Tsvetkov.Values obtained for h assuming the solute molecule to be a rigid, stiff chain, range between 1.3 to 2 Å. One notices that the h value close to 1.5 Å is found for the three following molecular weights: 1.8 × 105, 1.7 × 105, and 1.5 × 105. They are, in fact, the samples having a length in good quantitative agreement with that of the rigid segment determined by the method of Vitovskaya and Tsvetkov. This rigid segment corresponds to a sample of 700 ± 100 monomer units.The analysis of the experimental data of poly(γ-benzyl-L-glutamate) in dichloroacetic acid indicates that, in addition to the formation of hydrogen bonds, other interactions between the polypeptide and the solvent are present.In summary, we may conclude that the study of the helix–coil transition using hydrodynamic measurements is judged satisfactory but the determination of characteristic dimensions used to describe exactly the conformation of the macromolecule is somewhat ambiguous. One major problem is the degree of flexibility encountered with high molecular weight chains. However, to get around this difficulty, we propose, according to our results, a method which consists in determining the number of monomer units within a rigid segment from the different values found for h and then the dimensions from the samples for which the chain length is in good agreement with that of a rigid segment thus determined.

Sign in / Sign up

Export Citation Format

Share Document