ATP formation onset lag and post-illumination phosphorylation initiated with single-turnover flashes. III. Characterization of the ATP formation onset lag and post-illumination phosphorylation for thylakoids exhibiting localized or bulk-phase delocalized energy coupling

1988 ◽  
Vol 20 (1) ◽  
pp. 129-154 ◽  
Author(s):  
William A. Beard ◽  
Richard A. Dilley
Keyword(s):  
Energy Coupling ◽  
Bulk Phase ◽  
Single Turnover ◽  
Atp Formation

Kinetic characterization of a cis- and trans-acting M2+-independent DNAzyme that depends on synthetic RNaseA-like functionality — Burst-phase kinetics from the coalescence of two active DNAzyme folds

2007 ◽  
Vol 85 (4) ◽  
pp. 313-329 ◽  
Author(s):  
Richard Ting ◽  
Jason M Thomas ◽  
David M Perrin
Keyword(s):  
Steady State ◽  
Rate Constant ◽  
Acid Catalyst ◽  
Initial Population ◽  
Substrate Complex ◽  
Single Turnover ◽  
A Value ◽  
Burst Phase ◽  
Cis And Trans

This work describes the kinetics of the DNAzyme 925-11, a combinatorially selected, M2+-independent ribophosphodiesterase that is covalently modified with both cationic amines and imidazoles. At 13 °C, cis- and trans-cleaving constructs of 925-11 demonstrate the highest rate constants reported to date for any M2+-independent nucleic acid catalyst, investigated at physiological ionic strength and pH 7.5 (0.3 min–1 for self cleavage and 0.2 min–1 for intermolecular cleavage). In contrast to the cis-cleaving species, single-turnover experiments with the trans-cleaving species exhibit biphasic cleavage data, suggesting the presence of two conformations of the catalyst–substrate complex. Pulse–chase experiments demonstrate that both complexes lead to substrate cleavage. Under multiple-turnover conditions, the higher rate constant appears in a burst phase that decays to a slower steady state exhibiting a rate constant of 0.0077 min–1, a value approximating that of the slow-cleaving phase seen in single-turnover experiments. Slow product release is excluded as the source of the burst phase. An integrated rate equation is derived to describe burst-phase kinetics based on the funneling of the initial population of fast-cleaving conformation into a steady-state population composed largely of the slow-cleaving conformation.Key words: RNase mimics, DNAzymes, ribozymes, kinetics, RNA cleavage.

scholarly journals Cage effects control the mechanism of methane hydroxylation in zeolites

Science ◽  
2021 ◽  
Vol 373 (6552) ◽  
pp. 327-331
Author(s):  
Benjamin E. R. Snyder ◽  
Max L. Bols ◽  
Hannah M. Rhoda ◽  
Dieter Plessers ◽  
Robert A. Schoonheydt ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Spectroscopic Characterization ◽  
Single Turnover ◽  
Small Pore ◽  
Conversion Of Methane ◽  
Hindered Diffusion ◽  
Cage Effects

Catalytic conversion of methane to methanol remains an economically tantalizing but fundamentally challenging goal. Current technologies based on zeolites deactivate too rapidly for practical application. We found that similar active sites hosted in different zeolite lattices can exhibit markedly different reactivity with methane, depending on the size of the zeolite pore apertures. Whereas zeolite with large pore apertures deactivates completely after a single turnover, 40% of active sites in zeolite with small pore apertures are regenerated, enabling a catalytic cycle. Detailed spectroscopic characterization of reaction intermediates and density functional theory calculations show that hindered diffusion through small pore apertures disfavors premature release of CH3 radicals from the active site after C-H activation, thereby promoting radical recombination to form methanol rather than deactivated Fe-OCH3 centers elsewhere in the lattice.

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