Structural basis for the variation of pH-dependent redox potentials of Pseudomonas cytochromes c-551

Biochemistry ◽  
1984 ◽  
Vol 23 (8) ◽  
pp. 1831-1838 ◽  
Author(s):  
Fiona A. Leitch ◽  
Geoffrey R. Moore ◽  
Graham W. Pettigrew
Keyword(s):  
Structural Basis ◽  
Redox Potentials ◽  
Cytochromes C ◽  
Ph Dependent

scholarly journals Marked structural rearrangement of mannose 6-phosphate/IGF2 receptor at different pH environments

2020 ◽  
Vol 6 (7) ◽  
pp. eaaz1466 ◽  
Author(s):  
Rong Wang ◽  
Xiaofeng Qi ◽  
Philip Schmiege ◽  
Elias Coutavas ◽  
Xiaochun Li
Keyword(s):  
Cell Surface ◽  
Structural Rearrangement ◽  
Repeated Sequences ◽  
Structural Basis ◽  
Acidic Ph ◽  
Surface Receptors ◽  
Ligand Dissociation ◽  
Ph Dependent ◽  
Endocytic Compartments ◽  
Dissociated State

Many cell surface receptors internalize their ligands and deliver them to endosomes, where the acidic pH causes the ligand to dissociate. The liberated receptor returns to the cell surface in a process called receptor cycling. The structural basis for pH-dependent ligand dissociation is not well understood. In some receptors, the ligand binding domain is composed of multiple repeated sequences. The insulin-like growth factor 2 receptor (IGF2R) contains 15 β strand–rich repeat domains. The overall structure and the mechanism by which IGF2R binds IGF2 and releases it are unknown. We used cryo-EM to determine the structures of the IGF2R at pH 7.4 with IGF2 bound and at pH 4.5 in the ligand-dissociated state. The results reveal different arrangements of the receptor in different pH environments mediated by changes in the interactions between the repeated sequences. These results have implications for our understanding of ligand release from receptors in endocytic compartments.

scholarly journals Some reactions of carbon monoxide and oxygen with carbodi-imide-modified cytochrome c

1991 ◽  
Vol 276 (1) ◽  
pp. 121-124
Author(s):  
A J Mathews ◽  
T Brittain
Keyword(s):  
Cytochrome C ◽  
Flash Photolysis ◽  
Intermediate Phase ◽  
Cross Linking ◽  
Intramolecular Electron Transfer ◽  
Electron Transfer Process ◽  
Absorbance Change ◽  
Cytochromes C ◽  
Ph Dependent ◽  
Slow Kinetic

The reactivity of carbodi-imide-modified tuna and horse heart cytochromes c with the ferrous ion ligands CO and O2 has been studied. Both modified cytochromes bind one molecule of CO. Stopped-flow and flash-photolysis experiments indicate the presence of three kinetic processes in the reaction of the cytochromes with CO. The second-order rate constants associated with all three kinetic process are pH-independent being 2.8 x 10(5) M-1.s-1, 3.8 x 10(4) M-1.s-1 and 4 x 10(3) M-1.s-1 under all conditions studied. The concentration-dependence of the contributions made by each of the processes to the overall absorbance change indicates that the fast and slow kinetic phases are associated with two forms of the cytochromes which are in equilibrium, whereas the intermediate phase arises from a separate cytochrome species. The quantum yield for the photodissociation of CO from the ferrous cytochromes is unusually low. Both modified cytochromes are capable of binding and reducing O2. In the presence of excess reductant, the modified cytochromes can catalytically reduce large molar excesses of O2. In the absence of excess reducing agent, the oxy complex initially formed undergoes a pH-dependent intramolecular electron-transfer process with half-life approx. 10 min. EDC [1-ethyl-3-(3-dimethylaminopropyl)carbodi-imide]-promoted internal cross-linking is proposed to account for differences between the EDC-modified proteins and carboxymethylated cytochrome c.

Some Physicochemical Peculiarities of Poplar Plastocyanins a and b

2009 ◽  
Vol 64 (5-6) ◽  
pp. 399-404 ◽  
Author(s):  
Petya K. Christova ◽  
Anthony A. Donchev ◽  
Alexandra C. Shosheva ◽  
Vladimir I. Getov ◽  
Mitko I. Dimitrov
Keyword(s):  
Plant Species ◽  
Ph Dependence ◽  
Equilibrium Constants ◽  
The Other ◽  
Redox Potentials ◽  
Extinction Coefficients ◽  
Structural Differences ◽  
Ph Dependent ◽  
Ph Range ◽  
Reduced Forms

The redox potentials of poplar plastocyanins a and b (PCa, PCb) were determined by spectro photometric titrations of their reduced forms with [Fe(CN)6]3-. It was found that the two isoforms have the following millimolar extinction coefficients ε597, equilibrium constants Keq of one-electron exchange with [Fe(CN)6]4-/[Fe(CN)6]3-, and standard electron potentials E0′: PCa: ε597 = (4.72 ± 0.08) mM-1 cm-1, Keq = 0.133 ± 0.009, E0′ = (354 ± 11) mV; PCb: ε597 = (5.23 ± 0.16) mM-1 cm-1, Keq = 0.175 ± 0.010, E0′ = (363 ± 12) mV. The pH dependence of the redox potential of PCb was studied too. It was found, that the value of E0′ for PCb is constant in the pH range 6.5 - 9.5, but decreases in the range 4.8 - 6.5. On the whole, the dependence resembles that of PC from some well-known plant species, including poplar PCa. The changes of E0′ in the pH-dependent region for poplar PCb, however, are smaller and are 13 mV per pH unit, whereas in the other well-known plant species the changes are about 50 - 60 mV per pH unit. It has been assumed that the weaker pH dependence of E0′ of PCb accounts for some structural differences between PCa and PCb

Diversified Structural Basis of a Conserved Molecular Mechanism for pH-Dependent Dimerization in Spider Silk N-Terminal Domains

ChemBioChem ◽  
2015 ◽  
Vol 16 (12) ◽  
pp. 1720-1724 ◽  
Author(s):  
Martins Otikovs ◽  
Gefei Chen ◽  
Kerstin Nordling ◽  
Michael Landreh ◽  
Qing Meng ◽  
...  
Keyword(s):  
Molecular Mechanism ◽  
Spider Silk ◽  
Structural Basis ◽  
Ph Dependent ◽  
Terminal Domains

Electrochemical and Spectroelectrochemical Characterization of Water-soluble, β-Pyrrolebrominated Cobalt Porphyrins

1998 ◽  
Vol 02 (05) ◽  
pp. 429-437 ◽  
Author(s):  
FRANCIS D'SOUZA ◽  
YI-YING HSIEH ◽  
G. R. DEVIPRASAD
Keyword(s):  
Water Soluble ◽  
Redox Couple ◽  
Redox Potentials ◽  
Complete Elimination ◽  
Porphyrin Derivatives ◽  
Cobalt Porphyrins ◽  
Bulk Electrolysis ◽  
Ph Conditions ◽  
Ph Dependent

The electrochemical and spectroelectrochemical characterization of two water-soluble porphyrins, namely the tetrachloro salt of cobalt(II) tetrakis-(N-methyl pyridyl)-β-octabromoporphyrin, [( Br 8 TMPyP ) Co II] Cl 4, and the tetrasodium salt of cobalt(II) tetrakis-(4-sulfonatophenyl)-β-octabromoporphyrin, Na 4[( Br 8 TPPS ) Co II], under different pH conditions is reported. The investigated porphyrins are highly non-planar and electron-deficient owing to the presence of eight bromides at the β-pyrrole positions and the four meso-aryl substituents. The redox potentials corresponding to the first oxidation and first reduction are shifted positively compared with the redox potentials of the respective unbrominated porphyrin derivatives. Spectroelectrochemical studies reveal the formation of a cobalt(III) complex during the first oxidation of both cobalt porphyrins. The first reduction of Br 8 TPPS ) Co II]4− results in a cobalt(I) complex, while involvement of the peripheral N-methyl pyridyl groups in the case of Br 8 TMPyP ) Co II]4+ is suggested. The peak potentials of the first oxidation corresponding to a Co II/ Co III redox couple of both investigated compounds are found to be pH-dependent. Debromination of the β-pyrrole bromo substituents of Br 8 TMPyP ) Co II]4+ at more negative potentials is observed. The UV-vis spectrum obtained after bulk electrolysis of Br 8 TMPyP ) Co II]4+ at −1.0 V vs Ag / AgCl followed by reoxidation at 0.2 V indicates complete elimination of the bromo substituents of the porphyrin periphery.

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