Stereochemical constraints in peptide design: Analysis of the influence of a disulfide bridge and an α-aminoisobutyryl residue on the conformation of a hexapeptide

The competing effects of a disulfide bridge and an α-aminoisobutyryl residue (Aib) in determining the conformation of a hexapeptide have been investigated, by comparing the cyclic disulfide (1) and the acylic peptide Boc-Cys(SBzl)-Val-Aib-Ala-Leu-Cys(SBzl)-NHMe ( 2 ). Previously published nmr and crystallographic studies [R. Kishore, S. Raghothama, and P. Balaram (1987) Biopolymers, Vol. 26, pp. 873–891; I. L. Karle, R. Kishore, S. Raghothama, & P. Balaram, (1988) Journal of the American Chemical Society Vol. 110, pp. 1958–1963] have established an antiparallel β-hairpin structure for 1 with a central Aib-Ala β-turn. A comparison of nmr data for 1 and 2 in chloroform and dimethylsulfoxide reveals that the acyclic peptide is conformationally labile. Evidence for a 3₁₀-helical conformation in CDCl₃ is obtained from sensitivity of NH chemical shifts to temperature and solvent perturbation and low J_HNCαH values. Studies in solvent mixtures establish a conformational transition on going from CDCl₃ to (CD₃)₂SO. The changes in NH nmr parameters, together with the observation of several interresidue C H-N_{i + 1}H nuclear Overhauser effects support a conformation having a central β-turn with extended arms in (CD₃)₂SO. A single Aib residue appears to stabilize a helix in apolar solvents, for the acyclic hexapeptide, while the disulfide bridge serves to lock the β-hairpin conformation. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterization of three primary oligomers of alpha-L-glutamic acid. I

In the present work, the synthesis of the three primary oligomers of α-L -glutamic acid is described; the general formula is the following: [I] The choice of protective groups at the both ends of the chain allows for the good solubility in the water and the liberation of free carboxyl groups on the side chain. Thus, models are obtained for the study of thermodynamic properties of solutions and especially of the interactions between polyanions and cations. The prepared products are characterized by different techniques such as mass spectrometry potentiometry, tonometry, and thin-layer chromatography. The results are in agreement and lead to the conclusions that the molecules have the general formula of [I] and are stereoregular.     

Application of the nearest-neighbor Ising model to the helix-coil transition of polypeptides in mixed organic solvents.

Using the formalism of nearest-neighbor Ising model and assuming that the allowed states for a monomeric unity of a polypeptide chain in solutions containing strong acids are E (helix), C (coil), and CS (solvent-bonded coil), the partition function of the system was deduced analytically. Equations were obtained which permitted the prediction of the characteristic thermodynamic behavior of the helix–coil transition under these conditions. These equations were used to examine critically the possible correlations between experimental data obtained using different techniques. Particular attention was devoted to quantities called “transition enthalpies,” obtained from the slope of the transition curves at the point where the helix fraction is one-half (ΔH), or for measurements of the heat of solution of the polymer over the total range of solvent composition (ΔH), or from heat capacity measurements taken at various temperatures (ΔH). Literature data of ΔH(j = opt, sol, cal) for the system poly-γ-benzyl-L -glutamate in mixtures of dichloroacetic acid and 1,2-dichloroethane were carefully analyzed.     

Issue Information

Subaerial miroalgae form conspicuous biofilms on the bark surface of European beech trees (Fagus sylvatica) in temperate deciduous forests. ?tifterová and Neustupa investigated the variation in community structure of these covers on a small spatial scale. See ?tifterová and Neustupa in pages 299–311. Cover picture from: Article link here

     

Potentiometric neutralization of oligomers represented by the general formula shown was studied. II (author's transl)

Potentiometric neutralization of oligomers represented by the general formula shown was studied. The intrinsic pK of carboxyl function was found to be 4.40 at 25°C; the variation of the apparent pK_a, ΔK(α), was studied as a function of the degree of neutralization: the influence of the degree of neutralization on the accumulation of ionic sites along the chain is clearly shown. The experimental curves of polyglutamic acid allowed us to deduce the sequence of ionic selectivity and the energy of conformational transition. The theoretical interpretation of the results was proposed in terms of the rod like model from Katchalsky's theory. The intrinsic pK_o for the polymer was set equal to the value experimentally obtained on oligomers. By activity measurements on Na⁺ and Ca²⁺ counterions in salt-free solutions, the free fraction of counterions was deduced on the different samples. The results were interpreted with the electrostatic model previously proposed; in this view, the oligomers are assimilated to imaginary polyelectrolytes. This allowed us to determine the values of ΔpK and the fraction of free ions at the same time.     

Etude experimentale de L′auto-association des molécules modèles dipeptidiques. III. Influence de la dimerisation stéréosélective sur les spectres de résonance magnétique protonique

Proton magnetic resonance spectra of model dipeptide molecules R₁–C′₁O₁–N₂H₂–CHR₂–C′₂O₂–N₃H₃–R₃ in CCl₄ solutions exhibit splited signals when investigating on mixtures of L and D enantiomers differing from the racemic composition. The major effect is observed on amide proton signals which are the ones most sensitive to the ratio of aggregation. The stereoselective dimerization of enantiomeric molecules in the so-called C₅ conformational state is shown to be responsible for such a phenomenon, the intensity of which depends on the bulkiness of the side chain R₂. A theoretical approach is proposed which gives predictions in close agreement with our own experimental findings.     

Das Gesetz der absoluten Geschwindigkeiten biologischer Prozesse

The dependency of the velocity of biological processes from the temperature is described by the “Law of absolute velocity of biological processes”, which has only the individual parameters energy of activation ΔE, and the universal constant C. The law holds for all biological processes and is expressed by the equation: where C is: .     

Front Cover: Optoacoustic mesoscopy analysis and quantitative estimation of specific imaging metrics in Fitzpatrick skin phototypes II to V (J. Biophotonics 9/2019)

Raster Scanning Optoacoustic Mesoscopy (RSOM) is a novel optoacoustic imaging modality that offers non‐invasive, label‐free, high resolution (~7 µm axial, ~30 µm lateral) imaging up to 1–2 mm below the skin. This paper aims to provide quantitative estimation of specific imaging metrics, like total blood volume, vessel diameter, and melanin signal intensity for in vivo skin imaging of human subjects with Fitzpatrick (FP) skin types between II to V. Further details can be found in the article by Xiuting Li, Dinish U. S., Juan Aguirre, et al. ( e201800442 ).

     

Issue Information

Bloom‐forming Raphidophyceae from the Brazilian coast. Chattonella subsalsa (left), C. antiqua (center), and Heterosigma akashiwo (right) were photographed at the same view. See Branco et al. in this issue. The link to the article here

     

Confidence Estimation of an Unknown Component of the Vector of Regressor Variables in Multivariate Linear Regression

The model used in this paper is Y = Xβ, where with unknown x₀. Estimators of x₀ are derived by putting β_mx₀ =β_m+1 regarding β_m+1 as a new unknown parameter. Formally we use the model Y = X₁β₊ + e where β′₊ = (β₀, …β_m+1 and Then β_m+1/ β_m is a point estimator of x₀. Assuming normality for e and taking the random variable z=β_mx₀?β_m+1 we get a t-distributed variable and finally a confidence estimator of x₀. The formulas are applied in dose response relations in antibiotic assays refering to a standard. Now we can take into account not only the dependence on the dose/concentration but also on the position on the test agar plate where the test solution is filled in. As a consequence the confidence interval of the unknown dose/concentration x₀ becomes shorter and by it the statements more precise.     

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Cover Image Evening sun bathing flowers of Cymbidium dayanum. Photographed by Naoto Sugiura, Minami-Osumi, Kagoshima, Japan.

     

Front Cover: Spectral correction for handheld optoacoustic imaging by means of near‐infrared optical tomography in reflection mode (J. Biophotonics 1/2019)

Optoacoustics (OA) is combined with near‐infrared optical tomography (NIROT) in reflection mode to quantitatively image vasculature oxygen saturation (SO2) levels in phantoms containing vessels at depths up to 25 mm. Using NIROT to estimate the light fluence, the OA signals' spectral distortion was reduced from 60–150% to 10–20%. Results suggest that SO₂ levels can be determined with <10% error and that temporal changes can be monitored with even better accuracy. Further details can be found in the article by Leonie Ulrich, Linda Ahnen, Hidayet Günhan Akarçay, et al. ( e201800112 ).

     

On the Effects of Departure from Normality on the F-Ratios in a Nested Random Effect Model by Mixture of Normals

In this paper we consider the following nested random effect model where the α_i's, the β_ij's and the e_ijk are independent random variables. By assuming that these variables follow a mixture of two normal densities, we study the effects of departure from normality on the classical JT-tests for variance components. It is shown that the departure from normality has little effects on the type 1 error and the power function; this indicates that the classical F-tests are quite robust with respect to departure from normality.     

Issue Information

Cover Image The pollinators of Camellia pubipetala: sunbird Aethopyga christinae (left) and honeybee Apis cerana (right). Both pictures were taken by Sheng-feng Chai, at Longhushan, Jiangxi Province, China.

     

Issue Information

In situ photograph of Lobophora coquilleae sp. nov. from Papua New Guinea. See Vieira et al. in this issue. Cover picture from: Article link here

     

Inside Cover: Fingerprint‐to‐CH stretch continuously tunable high spectral resolution stimulated Raman scattering microscope (J. Biophotonics 9/2019)

A novel design of an SRS microscope exploiting spectral pulse shaping allows measurement of fingerprint to CH‐stretch SRS spectra without any modification of the optical setup. High spectral resolution over a broad vibrational range allows label‐free quantitative imaging of biological samples. An exemplary SRS broadband spectrum of lipid droplets in a liver cancer cell is shown in the picture. Further details can be found in the article by Sergey P. Laptenok, Vijayakumar P. Rajamanickam, Luca Genchi, et al. ( e201900028 ).

     

Issue Information

The estimated life span of Halimeda from a new recruit to a fertile plant. See Mayakun and Prathep in this issue. Cover picture from: Article link here

     

Inside Front Cover: Dynamic visualization of the recovery of mouse hepatobiliary metabolism to acetaminophen‐overdose damage (J. Biophotonics 3/2019)

In this work, intravital multiphoton microscopy was used to image and quantify hepatobiliary metabolism of 6‐carboxyfluorescein diacetate in the recovery of acetaminophen‐overdose mice. It was found that the excretion of the probe molecule was time‐dependent and hepatobiliary metabolism is higher in recovered mice, suggesting that newly regenerated hepatocytes have higher metabolic capabilities. This approach may be further developed applied to studying drug‐induced hepatotoxicity in vivo. Further details can be found in the article by Feng‐Chieh Li, Sheng‐Lin Lee, Hung‐Ming Lin, et al. ( e201800296 ).

     

Cover Image,Volume 92, Issue 5

Front Cover: The cover image is based on the Research Article Transmembrane proteins—Different anchoring systems by Irena Roterman et al., https://doi.org/10.1002/prot.26646

     

Transfer function matrix of the continuous cultivation system of Morchella crassipes in ammonia base waste sulfite liquor

A continuous stirred tank fermentor (CSTF) used for cultivation of the fungus Morchella crassipes in ammonia base waste sulfite liquor (NH₃-WSL) was considered as a multivariable linear system around its operating point. Pulse testing on the inputs (inlet jacket temperature, inlet pH, inlet substrate concentration) and their responses at the outputs (biomass, outlet temperature, outlet jacket temperature, outlet pH, outlet substrate concentration) were used for numerical determination of the transfer function matrix: