scholarly journals The porphyrin ring rather than the metal ion dictates long-range electron transport across proteins suggesting coherence-assisted mechanism

2020 ◽  
Vol 117 (51) ◽  
pp. 32260-32266
Author(s):  
Yuval Agam ◽  
Ramesh Nandi ◽  
Alexander Kaushansky ◽  
Uri Peskin ◽  
Nadav Amdursky
Keyword(s):  
Long Range ◽  
Metal Ion ◽  
Electron Mediator ◽  
Metal Centers ◽  
Biologically Relevant ◽  
Natural Systems ◽  
Redox Center ◽  
Fundamental Biological Process ◽  
Metal Redox ◽  
Electron Mediators

The fundamental biological process of electron transfer (ET) takes place across proteins with common ET pathways of several nanometers. Recent discoveries push this limit and show long-range extracellular ET over several micrometers. Here, we aim in deciphering how protein-bound intramolecular cofactors can facilitate such long-range ET. In contrast to natural systems, our protein-based platform enables us to modulate important factors associated with ET in a facile manner, such as the type of the cofactor and its quantity within the protein. We choose here the biologically relevant protoporphyrin molecule as the electron mediator. Unlike natural systems having only Fe-containing protoporphyrins, i.e., heme, as electron mediators, we use here porphyrins with different metal centers, or lacking a metal center. We show that the metal redox center has no role in ET and that ET is mediated solely by the conjugated backbone of the molecule. We further discuss several ET mechanisms, accounting to our observations with possible contribution of coherent processes. Our findings contribute to our understanding of the participation of heme molecules in long-range biological ET.

scholarly journals Donor Atom Preference of Organoruthenium and Organorhodium Cations on the Interaction with Novel Ambidentate (N,N) and (O,O) Chelating Ligands in Aqueous Solution

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3586
Author(s):  
Sándor Nagy ◽  
András Ozsváth ◽  
Attila Cs. Bényei ◽  
Etelka Farkas ◽  
Péter Buglyó
Keyword(s):  
Aqueous Solution ◽  
Metal Ion ◽  
Platinum Group Metal ◽  
Molecular Structures ◽  
Chelating Ligands ◽  
Metal Ion Binding ◽  
Biologically Relevant ◽  
X Ray Crystallography ◽  
Ligand Ratio ◽  
Ph Range

Two novel, pyridinone-based chelating ligands containing separated (O,O) and (Namino,Nhet) chelating sets (Namino = secondary amine; Nhet = pyrrole N for H(L3) (1-(3-(((1H-pyrrole-2-yl)methyl)amino)propyl)-3-hydroxy-2-methylpyridin-4(1H)-one) or pyridine N for H(L5) (3-hydroxy-2-methyl-1-(3-((pyridin-2-ylmethyl)amino)propyl)pyridin-4(1H)-one)) were synthesized via reduction of the appropriate imines. Their proton dissociation processes were explored, and the molecular structures of two synthons were assessed by X-ray crystallography. These ambidentate chelating ligands are intended to develop Co(III)/PGM (PGM = platinum group metal) heterobimetallic multitargeted complexes with anticancer potential. To explore their metal ion binding ability, the interaction with Pd(II), [(η6-p-cym)Ru]2+ and [(η5-Cp*)Rh]2+ (p-cym = 1-methyl-4-isopropylbenzene, Cp* = pentamethyl-cyclopentadienyl anion) cations was studied in aqueous solution with the combined use of pH-potentiometry, NMR and HR ESI-MS. In general, organorhodium was found to form more labile complexes over ruthenium, while complexation of the (N,N) chelating set was slower than the processes of the pyridinone unit with (O,O) coordination. Formation of the organoruthenium complexes starts at lower pH (higher thermodynamic stabilities of the corresponding complexes) than for [(η5-Cp*)Rh]2+ but, due to the higher affinity of [η6-p-cym)Ru]2+ towards hydrolysis, the complexed ligands are capable of competing with hydroxide ion in a lesser extent than for the rhodium systems. As a result, under biologically relevant conditions, the rhodium binding effectivity of the ligands becomes comparable or even slightly higher than their effectivity towards ruthenium. Our results indicate that H(L3) is a less efficient (N,N) chelator for these metal ions than H(L5). Similarly, due to the relative effectivity of the (O,O) and (N,N) chelates at a 1:1 metal-ion-to-ligand ratio, H(L5) coordinates in a (N,N) manner to both cations in the whole pH range studied while, for H(L3), the complexation starts with (O,O) coordination. At a 2:1 metal-ion-to-ligand ratio, H(L3) cannot hinder the intensive hydrolysis of the second metal ion, although a small amount of 2:1 complex with [(η5-Cp*)Rh]2+ can also be detected.

Electrochemical characterization of Cu(II) complexes of brain-related tau peptides

2021 ◽  
Vol 99 (7) ◽  
pp. 628-636
Author(s):  
Camilla Golec ◽  
Jose O. Esteves-Villanueva ◽  
Sanela Martic
Keyword(s):  
Metal Ions ◽  
Tau Protein ◽  
Metal Ion ◽  
Differential Pulse ◽  
Redox Couple ◽  
Peptide Sequence ◽  
Binding Studies ◽  
Biologically Relevant ◽  
Redox Active ◽  
Competition Binding

Metal ion dyshomeostasis plays an important role in diseases, including neurodegeneration. Tau protein is a known neurodegeneration biomarker, but its interactions with biologically relevant metal ions, such as Cu(II), are not fully understood. Herein, the Cu(II) complexes of four tau R peptides, based on the tau repeat domains, R1, R2, R3, and R4, were characterized by electrochemical methods, including cyclic voltammetry, square-wave voltammetry, and differential pulse voltammetry in solution under aerobic conditions. The current and potential associated with Cu(II)/(I) redox couple was modulated as a function of R peptide sequence and concentration. All R peptides coordinated Cu(II) resulting in a dramatic decrease in the current associated with free Cu(II), and the appearance of a new redox couple due to metallo–peptide complex. The metallo–peptide complexes were characterized by the irreversible redox couple at more positive potentials and slower electron-transfer rates compared with the free Cu(II). The competition binding studies between R peptides with Cu(II) indicated that the strongest binding affinity was observed for the R3 peptide, which contained 2 His and 1 Cys residues. The formation of complexes was also evaluated as a function of peptide concentration and in the presence of competing Zn(II) ions. Data indicate that all metallo–peptides remain redox active pointing to the potential importance of the interactions between tau protein with metal ions in a biological setting.

Efficient localization of a native metal ion within a protein by Cu2+-based EPR distance measurements

2019 ◽  
Vol 21 (20) ◽  
pp. 10238-10243 ◽  
Author(s):  
Austin Gamble Jarvi ◽  
Timothy F. Cunningham ◽  
Sunil Saxena
Keyword(s):  
Binding Site ◽  
Long Range ◽  
Metal Binding ◽  
Metal Ion ◽  
Native Metal ◽  
Distance Measurements ◽  
Metal Binding Site ◽  
Paramagnetic Metal

A native paramagnetic metal binding site in a protein is located with less than 2 Å resolution by a combination of double histidine (dHis) based Cu2+ labeling and long range distance measurements by EPR.

scholarly journals Hydrogen Sulfide and Persulfides Oxidation by Biologically Relevant Oxidizing Species

Antioxidants ◽  
2019 ◽  
Vol 8 (2) ◽  
pp. 48 ◽  
Author(s):  
Dayana Benchoam ◽  
Ernesto Cuevasanta ◽  
Matías Möller ◽  
Beatriz Alvarez
Keyword(s):  
Hydrogen Sulfide ◽  
Oxidation Products ◽  
Physiological Effects ◽  
Metal Centers ◽  
Biologically Relevant ◽  
Mammalian Tissues ◽  
Sulfenic Acids ◽  
Electrophilic Character

Hydrogen sulfide (H2S/HS–) can be formed in mammalian tissues and exert physiological effects. It can react with metal centers and oxidized thiol products such as disulfides (RSSR) and sulfenic acids (RSOH). Reactions with oxidized thiol products form persulfides (RSSH/RSS–). Persulfides have been proposed to transduce the signaling effects of H2S through the modification of critical cysteines. They are more nucleophilic and acidic than thiols and, contrary to thiols, also possess electrophilic character. In this review, we summarize the biochemistry of hydrogen sulfide and persulfides, focusing on redox aspects. We describe biologically relevant one- and two-electron oxidants and their reactions with H2S and persulfides, as well as the fates of the oxidation products. The biological implications are discussed.

Biologically relevant metal ion-dependent hydroxyl radical generation An update

FEBS Letters ◽  
1992 ◽  
Vol 307 (1) ◽  
pp. 108-112 ◽  
Author(s):  
Barry Halliwell ◽  
John M.C. Gutteridge
Keyword(s):  
Hydroxyl Radical ◽  
Metal Ion ◽  
Biologically Relevant ◽  
Radical Generation

Electronic tongue formed by sensors and biosensors containing phthalocyanines as electron mediators: Application to the analysis of red grapes

2014 ◽  
Vol 18 (01n02) ◽  
pp. 76-86 ◽  
Author(s):  
Cristina Medina-Plaza ◽  
Gema Revilla ◽  
Raquel Muñoz ◽  
José Antonio Fernández-Escudero ◽  
Enrique Barajas ◽  
...  
Keyword(s):  
Glucose Oxidase ◽  
Electronic Tongue ◽  
Principal Component ◽  
Carbon Paste ◽  
Electron Mediator ◽  
Enzyme Substrate ◽  
Voltammetric Sensors ◽  
The Individual ◽  
Electron Mediators

An electronic tongue formed by voltammetric sensors and biosensors containing phthalocyanines has been developed and used to analyze grapes of different varieties. The sensors are prepared using the carbon paste technique and have been chemically modified with different metallophthalocyanines. In turn, biosensors consist of carbon paste electrodes modified with phthalocyanines combined with tyrosinase or glucose oxidase. The response of the individual sensors towards model solutions of glucose and catechol have demonstrated that the voltammetric responses depend on the nature of the phthalocyanine, evidencing the important role of the electron mediator in the performance of the sensors. The capability of the system to discriminate grapes according to their sugar and their polyphenolic content has been evidenced using Principal Component Analysis. It has been demonstrated that the proposed array of sensors combines the advantages of classical phthalocyanine based sensors — that provide global information about the sample —, with the specificity of the enzyme substrate reaction typical of biosensors. For this reason, the selectivity of the multisensor system and its capability of discrimination is clearly improved when biosensors containing glucose oxidase or tyrosinase are included in the array.

An initial characterization of the proteolytic enzymes secreted by the adult stage of the human hookworm Necator americanus

Parasitology ◽  
1995 ◽  
Vol 110 (5) ◽  
pp. 555-563 ◽  
Author(s):  
A. Brown ◽  
J. M. Burleigh ◽  
E. E. Billett ◽  
D. I. Pritchard
Keyword(s):  
Serine Proteases ◽  
Metal Ion ◽  
Proteolytic Enzymes ◽  
Maximum Activity ◽  
Biologically Relevant ◽  
Necator Americanus ◽  
Recent Developments ◽  
Proteolytic Activities ◽  
Secretory Products ◽  
Ph Range

SUMMARYThe proteolytic activities present in adult Necator americanus excretory–secretory products have been assessed using biologically relevant, naturally occurring substrates (haemoglobin and fibrinogen) and a number of synthetic fluorogenic and chromogenic substrates. One broad peak of activity was observed against haemoglobin in the pH range 5 to 7, with maximum activity at pH 6·6, while fibrinogenolytic activity was shown to be greater at pH 3·5. Inhibition studies against haemoglobin, fibrinogen and synthetic substrates using a battery of appropriate protease inhibitors indicated the presence of a mixture of aspartyl, cysteinyl and serine proteases. Metal ion (Ca2+, Zn2+ and Fe2+) stimulation was demonstrated, with stimulation by Zn2+ being the most marked. These results are discussed in the context of recent developments in the field of parasite proteolytic enzymes, where they have been suggested as targets for immuno- and chemotherapy.

Complexation of Transuranic Ions by Humic Substances: Application of Laboratory Results to the Natural System

1996 ◽  
Vol 465 ◽  
Author(s):  
Ken Czerwinski ◽  
Jae-Il Kim
Keyword(s):  
Humic Acid ◽  
Humic Substances ◽  
Metal Ion ◽  
Ion Concentration ◽  
Mixed Species ◽  
Experimental Conditions ◽  
Aquifer System ◽  
Natural Systems ◽  
Species Formation ◽  
Laboratory Results

ABSTRACTEnvironmental investigations show transuranic ions sorb to humic substances. The resulting species are often mobile and are expected to be important vectors in the migration of transuranic ions in natural systems. However, theses environmental studies yield no quantitative data useful for modeling. Laboratory complexation experiments with transuranic ions and humic substances generate mermodynamic data required for complexation modeling. The data presented in this work are based on the metal ion charge neutralization model, which is briefly described. When a consistent complexation model is used, similar results are obtained from different experimental conditions, techniques, and laboratories. Trivalent transuranic ions (CM(III), AM(III)) have been extensively studied with respect to pH, ionic strength, origin of humic acid, and mixed species formation. The complexation of Np(V) has been examined over a large pH and metal ion concentration range with different humic acids. Some data does exist on the complexation of plutonium with humic acid, however further work is needed. Calculations on the Gorleben aquifer system using the thermodynamic data are presented. Critical information lacking from the mermodynamic database is identified.

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