Physical properties of lipid bilayers from EPR spin labeling and their influence on chemical reactions in a membrane environment

The influence of a variety of microenvironmental factors on the inherent reactivity of membrane-located reagents is poorly understood. A goal of this review is to provide detailed profiles of membrane properties, including hydrophobicity, oxygen and nitric oxide solubility and diffusion rates, bilayer penetration of metal ions and metal-ion complexes, and membrane order and fluidity, that can be obtained with EPR spin-labeling methods. These properties can drastically vary with membrane composition, membrane depth, and membrane domain formation, influencing the fate of chemical reactions that occur in a lipid bilayer environment.     

The reaction of alpha-synuclein with tyrosinase: possible implications for Parkinson disease

Oxidative stress appears to be directly involved in the pathogenesis of Parkinson disease. Several different pathways have been identified for the production of oxidative stress conditions in nigral dopaminergic neurons, including a pathological accumulation of cytosolic dopamine with the subsequent production of toxic reactive oxygen species or the formation of highly reactive quinone species. On these premises, tyrosinase, a key copper enzyme known for its role in the synthesis of melanin in skin and hair, has been proposed to take part in the oxidative chemistry related to Parkinson disease. A study is herein presented of the in vitro reactivity of tyrosinase with alpha-synuclein, aimed at defining the molecular basis of their synergistic toxic effect. The results presented here indicate that, in conformity with the stringent specificity of tyrosinase, the exposed tyrosine side-chains are the reactive centers of alpha-synuclein. The reactivity of alpha-synuclein depends on whether it is free or membrane bound, and the chemical modifications on the tyrosinase-treated alpha-synuclein strongly influence its aggregation properties. On the basis of our results, we propose a cytotoxic model which includes a possible new toxic role for alpha-synuclein exacerbated by its direct chemical modification by tyrosinase.     

Redox proteomics: from residue modifications to putative biomarker identification by gel- and LC-MS-based approaches

Quantitative determination of reactive oxygen species and reactive nitrogen species in body fluids, tissues or cells has always been problematic due to their high chemical reactivity and the resulting short half-life. This high reactivity may involve reversible and/or irreversible protein modifications, in particular the covalent oxidative modification of specific amino acid residues. Thus, the occurrence of reactive oxygen species and reactive nitrogen species can be monitored indirectly from the identification of specific protein-chemical footprints. In combination with classical gel-based proteomics or liquid chromatography labeling or label-free techniques, mass spectrometry has emerged as a powerful tool to identify these protein modifications in biological samples. In this review, we present the main methodological approaches for gel-based proteomics and quantitative mass spectrometry applied to oxidative protein modifications, mainly Cys. Representative examples from their application in identifying respective biomarkers in diseases related to oxidative stress are also presented.     

Computer Simulation of the Beta Structure,with Different Lattice Ions and Reactivity,of Hydroperoxo-Metal Complexes Using an Embedded-Cluster Method

The chemical properties of beta zeolite are interconnected with its structure in a complicated way. In general terms, the strength of the acid sites in the beta phase depends strongly on its structure, topology and composition. The quantum chemical calculations of the beta zeolite cluster model have been carried out in order to predict how the cluster's local structure influences the geometric parameters and thus affects the chemical functionality of the beta zeolite. Computer simulations of a beta zeolite model with one lattice aluminium, or boron, or titanium or vanadium ions and of its acidic centres have been carried out. The acidity of the framework oxygen atoms in the vicinity of the lattice atom centre has been calculated and compared. The reactivity of catalytic species comprisingthe lattice ion and a hydroperoxo ligand has been studied as an oxidising site.     

An experimental and theoretical study of Coprinus cinereus peroxidase-catalyzed biodegradation of isoelectronic to dioxin recalcitrants

Isoelectronic to dibenzo-p-dioxin (DBD) compounds (ID) containing nitrogen and/or sulfur atom instead of oxygen atom can be oxidized in the presence of fungal peroxidase. To elucidate the structure/activity relationship the redox potential of ID's was determined and correlated with calculated properties from ab initio calculations. The redox potential of ID's varied between 0.16 and 1.46 V versus standard calomel electrode (SCE) in acetonitrile. Spectral measurements and ab initio quantum chemical calculations showed that the redox potential correlated with the quantity of heteroatom conjugation with the 6π-aromatic system. The reactivity of ID's decreased if the redox potential of ID's increased. The calculations of docking and molecular dynamics revealed that all ID's may form the stable complexes in the active center of peroxidase. The acquired results permitted to conclude that low reactivity of ID's and their halogenated derivatives is associated with the high redox potential of recalcitrants.     

Oxidized phospholipids: from molecular properties to disease

Oxidized lipids are generated from (poly)unsaturated diacyl- and alk(en)ylacyl glycerophospholipids under conditions of oxidative stress. The great variety of reaction products is defined by the degree of modification, hydrophobicity, chemical reactivity, physical properties and biological activity. The biological activities of these compounds may depend on both, the recognition of the particular molecular structures by specific receptors and on the unspecific physical and chemical effects on their target systems (membranes, proteins). In this review, we aim at highlighting the molecular features that are essential for the understanding of the biological actions of pure oxidized phospholipids. Firstly, their chemical structures are described as a basis for an understanding of their physical and (bio)chemical properties in membrane- and protein-bound form. Secondly, the biological activities of oxidized phospholipids are discussed in terms of their unspecific effects on the membrane level as well as their potential interactions with specific targets (receptors) affecting a large set of (signaling) molecules. Finally, the role of oxidized phospholipids as important mediators in pathophysiology is discussed with emphasis on atherosclerosis.     

The Antigenic Properties of β-Lactoglobulin Examined with Mouse IgE Antibody

The effects of enzymic or chemical fragmentations and of chemical modifications on the antigenic properties of bovine β-Mactoglobulin were examined using specific mouse IgE antibody. The antigenic reactivity of β-Mactoglobulin derivatives was represented in terms of their ability to neutralize specific IgE antibodies assayed by passive cutaneous anaphylaxis in rat. The tryptic, chymotryptic or peptic hydrolysate free of native β-Mactoglobulin had no antigenic reactivity but the fragments obtained after CNBr cleavage retained the ability to bind the antibody. Modification of the sulfhydryl group, arginine or tryptophan residues and amino groups had no effect on antigenic reactivity but a little decrease in the reactivity was observed on the cleavage of the two disulfide bridges. These results suggest that one sulfhydryl group, two arginine and tryptophan residues and most of the amino groups are out of antigenic sites in β-Mactoglobulin and that the antigenicity depends on the conformation maintained by the disulfide bridges.     

Chemical properties of the functional groups of insulin.

The method of competitive binding [Kaplan, Stevenson & Hartley (1971) Biochem. J. 124, 289-299] with 1-fluoro-2,4-dinitrobenzene as the labelling reagent [Duggleby & Kaplan (1975) Biochemistry 14, 5168-5175] was used to determine the chemical properties, namely pK and reactivity, of the amino groups, the histidine residues and the tyrosine residues of the dimeric form of pig zinc-free insulin at 20.0 degrees C. The N-terminal glycine residue of the A-chain has a pK of 7.7 and a slightly higher than normal reactivity. The N-terminal phenylalanine residue of the B-chain has a pK of 6.9 and is approximately an order of magnitude more reactive than a corresponding amino group with the same pK value. The lysine epsilon-amino group has an unusually low pK of 7.0 but has approximately the expected reactivity of such a group. In the case of the two histidine and four tyrosine residues only the average properties of each class were determined. The histidine residues have a pK value of approx. 6.6, but, however, their reactivity is at least an order of magnitude greater than that of a free imidazole group. The tyrosine residues have a pK value of approx. 10, but their average reactivities are substantially less than for a free phenolic group. At alkaline pH values above 8 the reactivity of all the functional groups show sharp discontinuities, indicating that insulin is undergoing a structural change that alters the properties of these groups.     

N-Hydroxyguanidines oxidation by a N3S copper-complex mimicking the reactivity of Dopamine β-Hydroxylase

N-Aryl-N′-hydroxyguanidines are compounds that display interesting pharmacological properties but their chemical reactivity remains poorly investigated. Some of these compounds are substrates for the heme-containing enzymes nitric-oxide synthases (NOS) and act as reducing co-substrates for the copper-containing enzyme Dopamine β-Hydroxylase (DBH) [P. Slama, J.L. Boucher, M. Réglier, Biochem. Biophys. Res. Commun. 316 (2004) 1081-1087]. DBH catalyses the hydroxylation of the important neurotransmitter dopamine into norepinephrine in the presence of both molecular oxygen and a reducing co-substrate. Although many molecules have been used as co-substrates for DBH, their interaction at the active site of DBH and their role in mechanism are not clearly characterized. In the present paper, we have used a water-soluble copper-N₃S complex that mimics the Cu_B site of DBH, and aromatic N-hydroxyguanidines as reducers to address this question. N-Aryl-N′-hydroxyguanidines readily reduced copper(II) to Cu(I) and were oxidized into a nitrosoamidine as previously observed in reactions performed with purified DBH. These data describe for the first time the reactivity of N-aryl-N′-hydroxyguanidines with a water-soluble copper(II) complex and help to understand the interaction of co-substrates with copper at the active site of DBH.     

The unique chemistry of benzoxaboroles: Current and emerging applications in biotechnology and therapeutic treatments

Benzoxaboroles have garnered much attention in recent years due to their diverse applications in bio-sensing technology, material science, and therapeutic intervention. Part of the reason arises from the benzoxaboroles’ unique chemical properties, especially in comparison to their acyclic boronic acid counterparts. Furthermore, the low bio-toxicity combined with the high target specificity associated with benzoxaboroles make them very attractive as therapeutic agents. Herein, we provide an updated summary on the current knowledge of the fundamental chemical reactivity of benzoxaboroles, followed by highlighting their major applications reported to date.     

Similarities in melittin functional group reactivities during self-association and association with lipid bilayers.

Competitive labeling of melittin over a range of concentrations in the presence and absence of liposomes provides a series of "snapshots" of the chemical reactivities of melittin's intrinsic nucleophiles. Distinct trends in apparent reactivities were observed for the Gly-1 alpha-amino group and the epsilon-amino groups of Lys-7 and Lys-21 and -23, over a range of concentrations, providing evidence for different forms of associated melittin in solution. The monomer-tetramer transition can be followed, in accord with structural details derived from X-ray crystallography. The reactivity behavior of the alpha-amino group of Gly-1 and the epsilon-amino groups of Lys-21 and Lys-23 suggests these groups undergo similar perturbations in their microenvironments during the monomer-tetramer transition in free solution. Similar changes in reactivity behavior occur upon association of melittin monomers with bilayer-forming lipids. Together, these findings suggest that the local environments of the N- and C-terminal segments have similar physicochemical properties in both the solution tetramer and the lipid-associated complex. The concentration dependence of the chemical properties of melittin is correlated with surface accessibility calculations which are used to provide a framework for interpretation. Aspects of several previously proposed models of membrane lysis can be accounted for by concentration-dependent properties of melittin.     

E环为五元环三萜的结构研究进展

本文综述了E环为五元环的五环三萜烷、萜烯、及单氧取代物的光谱特征及相关化学性质方面的研究进展。     

Electronic factors and lipophilicity in the horseradish peroxidase-catalyzed oxidation of N,N-dialkylanilines with hydrogen peroxide and oxygen

Initial rates of N-dealkylation of 15 N, N-dialkylanilines with hydrogen peroxide and oxygen in the presence of the enzyme horseradish peroxidase are interpreted mainly in terms of electron availability on nitrogen. In these cases a mechanism similar to that postulated in the chemical oxidation of these substrates is suggested, and involves the formation of a cation radical. Lipophilicity acts as a limiting factor in the reaction, and highly hydrophilic and hydrophobic substrates deviate from the reactivity suggested by electronic factors toward higher and lower reactivity, respectively.     

Simple electrospray mass spectrometry detection of acylhomoserine lactones

Simple (non‐tandem) electrospray mass spectrometry (ESMS) can detect acyl homoserine lactones (AHL) in bacteriological media in picomole amounts. The chemical reactivity of AHLs and their extraction behaviour into ethyl acetate, coupled with detection in the ESMS, has shown that these lactones can be detected as the protonated pseudomolecular ions themselves as well as solvent and ammonium adducts, and as dimers. ESMS detects and identifies these molecules, utilizing simple chemical properties of AHLs. Copyright © 2005 John Wiley & Sons, Ltd.     

Structure and electronic properties of heme complexes with various ligands

The electronic and atomic structures, and the molecular dynamics of the atomic structure at 310 K of a set of heme complexes with His and Gly amino acids in the 5th coordination position and some ligands (O2, NO) in the 6th position were studied by ab initio (3-21G basis set) and semiempirical (PM3) quantum chemistry methods and the method of molecular dynamics. It was shown that the type of coordination of the imidazole ring influences the constant of chemical bonding of molecular oxygen of the complexes. On the other hand, NO and O2 molecules have different transinfluence on the ligand in the 5th coordination position. It was shown that temperature affects profoundly the atomic and electronic structures of the complexes, the tightness of chemical bonding and their reactivity.     

Peroxomanganese complexes as an aid to understanding redox-active manganese enzymes

Over the past 7 years, there have been a significant number of studies describing the structural and electronic properties, as well as the chemical reactivity, of synthetic peroxomanganese adducts. Many redox-active manganese enzymes, including manganese-containing superoxide dismutases, extradiol catechol dioxygenases, and ribonucleotide reductases, are proposed to feature peroxomanganese intermediates in their catalytic cycles. The recent efforts to model these intermediates using synthetic complexes have thus provided a strong complement to mechanistic studies of the enzymes. This review provides both a summary and a perspective of work in this area, with an emphasis on the relationship between geometric and electronic structure and chemical reactivity for η²-peroxomanganese(III) and η¹-alkylperoxomanganese(III) adducts.     

Cloning and expression of the Vitreoscilla hemoglobin gene in Enterobacter aerogenes: effect on cell growth and oxygen uptake

The hemoglobins found in unicellular organisms show a greater chemical reactivity, protect cells against oxidative stress and hence have been implicated in a wider variety of potential functions than those traditionally associated with animal and plant hemoglobins. There are well-documented studies showing that bacteria expressing Vitreoscilla hemoglobin (VHb), the first prokaryotic hemoglobin characterized, have better growth and oxygen uptake rates than VHb counterparts.