pH dependent catecholase activity of Fe(II) complexes of type [Fe(L)]X2 [L = N-(phenyl-pyridin-2-yl-methylene)-ethane-1,2-diamine; X = ClO4− (1), PF6− (2)]: Role of counter anion on turnover number

Crystallographic evidence suggests that the pH-dependent affinity of IgG molecules for the neonatal Fc receptor (FcRn) receptor primarily arises from salt bridges involving IgG histidine residues, resulting in moderate affinity at mildly acidic conditions. However, this view does not explain the diversity in affinity found in IgG variants, such as the YTE mutant (M252Y,S254T,T256E), which increases affinity to FcRn by up to 10×. Here we compare hydrogen exchange measurements at pH 7.0 and pH 5.5 with and without FcRn bound with surface plasmon resonance estimates of dissociation constants and FcRn affinity chromatography. The combination of experimental results demonstrates that differences between an IgG and its cognate YTE mutant vary with their pH-sensitive dynamics prior to binding FcRn. The conformational dynamics of these two molecules are nearly indistinguishable upon binding FcRn. We present evidence that pH-induced destabilization in the CH2/3 domain interface of IgG increases binding affinity by breaking intramolecular H-bonds and increases side-chain adaptability in sites that form intermolecular contacts with FcRn. Our results provide new insights into the mechanism of pH-dependent affinity in IgG-FcRn interactions and exemplify the important and often ignored role of intrinsic conformational dynamics in a protein ligand, to dictate affinity for biologically important receptors.

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Nitric Oxide Does Not Inhibit but Is Metabolized by the Cytochrome bcc-aa3 Supercomplex

International Journal of Molecular Sciences ◽

10.3390/ijms21228521 ◽

2020 ◽

Vol 21 (22) ◽

pp. 8521 ◽

Cited By ~ 1

Author(s):

Elena Forte ◽

Alessandro Giuffrè ◽

Li-shar Huang ◽

Edward A. Berry ◽

Vitaliy B. Borisov

Keyword(s):

Nitric Oxide ◽

Active Site ◽

Protective Role ◽

Terminal Oxidase ◽

O2 Consumption ◽

Turnover Number ◽

Terminal Oxidases ◽

Reducing Conditions ◽

No Consumption

Nitric oxide (NO) is a well-known active site ligand and inhibitor of respiratory terminal oxidases. Here, we investigated the interaction of NO with a purified chimeric bcc-aa3 supercomplex composed of Mycobacterium tuberculosis cytochrome bcc and Mycobacterium smegmatisaa3-type terminal oxidase. Strikingly, we found that the enzyme in turnover with O2 and reductants is resistant to inhibition by the ligand, being able to metabolize NO at 25 °C with an apparent turnover number as high as ≈303 mol NO (mol enzyme)−1 min−1 at 30 µM NO. The rate of NO consumption proved to be proportional to that of O2 consumption, with 2.65 ± 0.19 molecules of NO being consumed per O2 molecule by the mycobacterial bcc-aa3. The enzyme was found to metabolize the ligand even under anaerobic reducing conditions with a turnover number of 2.8 ± 0.5 mol NO (mol enzyme)−1 min−1 at 25 °C and 8.4 µM NO. These results suggest a protective role of mycobacterial bcc-aa3 supercomplexes against NO stress.

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Mechanistic Observations on the Role of the Stannous Ion in Caries Lesion De- and Remineralization

Caries Research ◽

10.1159/000446849 ◽

2016 ◽

Vol 50 (4) ◽

pp. 378-382 ◽

Cited By ~ 4

Author(s):

Frank Lippert

Keyword(s):

Factorial Design ◽

Surface Hardness ◽

Acid Resistance ◽

Design Studies ◽

Mineral Distribution ◽

Caries Lesion ◽

Stannous Ion ◽

Ph Dependent

Two mechanistic, laboratory, factorial design studies were conducted to investigate the effect of the stannous ion (Sn2+) in the absence or presence of fluoride on caries lesion de- and remineralization. Study I was concerned with determining changes in mineral distribution of subsurface lesions, whereas study II investigated changes in surface hardness of surface-softened lesions as a function of pH. Study I showed that Sn2+ modulates the effects of fluoride by preventing lamination. Study II revealed that the effect of Sn2+ on rehardening is pH dependent. Neither study demonstrated synergy between Sn2+ and fluoride, yet interactions were observed. Sn2+ does interfere with remineralization to some extent although it provided acid resistance. The role of Sn2+ in the caries process is complex.

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pH-dependent fusion of didodecyl phosphate vesicles: role of hydrogen-bond formation and membrane fluidity

The Journal of Physical Chemistry ◽

10.1021/j100326a034 ◽

1988 ◽

Vol 92 (15) ◽

pp. 4416-4420 ◽

Cited By ~ 15

Author(s):

Leo A. M. Rupert ◽

Jan F. L. Van Breemen ◽

Dick Hoekstra ◽

Jan B. F. N. Engberts

Keyword(s):

Hydrogen Bond ◽

Membrane Fluidity ◽

Bond Formation ◽

Hydrogen Bond Formation ◽

Ph Dependent

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Niobium on BEA Dealuminated Zeolite for High Selectivity Dehydration Reactions of Ethanol and Xylose into Diethyl Ether and Furfural

Nanomaterials ◽

10.3390/nano10071269 ◽

2020 ◽

Vol 10 (7) ◽

pp. 1269

Author(s):

Deborah S. Valadares ◽

Maria Clara H. Clemente ◽

Elon F. de Freitas ◽

Gesley Alex V. Martins ◽

José A. Dias ◽

...

Keyword(s):

Solid State ◽

Diethyl Ether ◽

High Selectivity ◽

Catalytic Properties ◽

Good Activity ◽

Green Solvent ◽

Turnover Number ◽

Dehydration Reactions ◽

Leveling Effect

In this work, we investigated the role of solid-state dealumination by (NH4)2SiF6 (25% Al removal and 13% Si insertion), the impregnation of niobium (10, 18, and 25 wt. %) on dealuminated *BEA (DB) zeolite and their catalytic properties in ethanol and xylose transformations. Among all the studied catalysts, 18%Nb-DB showed increased mesoporosity and external areas. A leveling effect in the number and strength of the proposed two sites (Brønsted and Lewis) present in the catalyst (n1 = 0.24 mmol g−1, −ΔH1 = 49 kJ mol−1, and n2 = 0.20 mmol g−1, –ΔH2 = 42 kJ mol−1) in the catalyst 18%Nb-DB, might be responsible for its good activity. This catalyst presented the highest selectivity for diethyl ether, DEE (97%) with 61% conversion after 50 ethanol pulses at 230 °C (turnover number, TON DEE = 1.15). These features allowed catalytically fruitful bonding of the ethanol molecules to the neighboring sites on the channels, facilitating bimolecular ether formation through a possible SN2 mechanism. The same catalyst was active and selective for transformation of xylose at 180 °C, showing 64% conversion and 51% selectivity for furfural (TON Furfural = 24.7) using water as a green solvent.

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