Termination Rates by Time-Resolved ESR. The N-Hydropyridinyl Radical in Solution and the Influence of Non-Uniform Radical Concentration on the Apparent Rate Constant

1984 ◽  
Vol 88 (5) ◽  
pp. 462-466 ◽  
Author(s):  
Rainer Leuschner ◽  
Holger Krohn ◽  
Jürgen K. Dohrmann
Keyword(s):  
Rate Constant ◽  
Apparent Rate Constant ◽  
Time Resolved ◽  
Radical Concentration

scholarly journals The fidelity of replication of the three-base-pair set adenine/thymine, hypoxanthine/cytosine and 6-thiopurine/5-methyl-2-pyrimidinone with T7 DNA polymerase

2004 ◽  
Vol 381 (3) ◽  
pp. 709-717 ◽  
Author(s):  
Harry P. RAPPAPORT
Keyword(s):  
Dna Polymerase ◽  
Rate Constant ◽  
Base Pair ◽  
Apparent Rate Constant ◽  
Polymerase Activity ◽  
Exonuclease Activity ◽  
Base Pairs ◽  
Error Frequency ◽  
Steady State Kinetics ◽  
Adenine Thymine

With the goal of constructing a genetic alphabet consisting of a set of three base pairs, the fidelity of replication of the three base pairs TH (5-methyl-2-pyrimidinone)/HS (6-thiopurine; thiohypoxanthine), C/H (hypoxanthine) and T/A was evaluated using T7 DNA polymerase, a polymerase with a strong 3′→5′ exonuclease activity. An evaluation of the suitability of a new base pair for replication should include both the contribution of the fidelity of a polymerase activity and the contribution of proofreading by a 3′→5′ exonuclease activity. Using a steady-state kinetics method that included the contribution of the 3′→5′ exonuclease activity, the fidelity of replication was determined. The method determined the ratio of the apparent rate constant for the addition of a deoxynucleotide to the primer across from a template base by the polymerase activity and the rate constant for removal of the added deoxynucleotide from the primer by the 3′→5′ exonuclease activity. This ratio was designated the eni (efficiency of net incorporation). The eni of the base pair C/H was equal to or greater than the eni of T/A. The eni of the base pair TH/HS was 0.1 times that of A/T for TH in the template and 0.01 times that of A/T for HS in the template. The ratio of the eni of a mismatched deoxynucleotide to the eni of a matched deoxynucleotide was a measure of the error frequency. The error frequencies were as follows: thymine or TH opposite a template hypoxanthine, 2×10−6; HS opposite a template cytosine, <3×10−4. The remaining 24 mismatched combinations of bases gave no detectable net incorporation. Two mismatches, hypoxanthine opposite a template thymine or a template TH, showed trace incorporation in the presence of a standard dNTP complementary to the next template base. T7 DNA polymerase extended the primer beyond each of the matched base pairs of the set. The level of fidelity of replication of the three base pairs with T7 DNA polymerase suggests that they are adequate for a three-base-pair alphabet for DNA replication.

Gold nanoparticles-coated chemically-reactive polymer colloids and the study of their catalytic kinetics

2014 ◽  
Vol 1641 ◽  
Author(s):  
Maolin Li ◽  
Vivian Zhong ◽  
Guofang Chen
Keyword(s):  
Gold Nanoparticles ◽  
Reaction Time ◽  
Rate Constant ◽  
Apparent Rate Constant ◽  
Reaction Rate ◽  
Catalytic Efficiency ◽  
Reduction Reaction ◽  
Assembly Method ◽  
Nitrophenol Reduction ◽  
Time Average

ABSTRACTRaspberry-like composite spheres based on chemically-reactive poly(glycidyl methacrylate) (PGMA) colloids as the cores coated with tunable size of gold nanoparticles were synthesized via a controlled assembly method. Kinetic study of 4-nitrophenol reduction by NaBH4 in the presence of poly(allylamine hydrochloride)-modified PGMA composite with tunable size of AuNPs (PGMA@PAH@AuNPs) was demonstrated. Effects of gold nanoparticles size and PGMA colloid diameter on the reaction time, average reaction rate and average turnover frequency (TOF), order of reaction (n) and apparent rate constant (kapp) were systematically investigated. Experimental results of our study showed composites with 3.4 ± 0.9 nm AuNPs have the best catalytic efficiency with the highest reaction order and apparent rate constant. The poisoning of product 4-aminophenol on PAH-modified PGMA colloid-supported gold nanocatalysts was evaluated using 4-nitrophenol/NaBH4 reduction reaction for the reaction time, average reaction rate, average TOF, order of reaction and apparent rate constant.

scholarly journals Coassembly of SecYEG and SecA Fully Restores the Properties of the Native Translocon

2018 ◽  
Vol 201 (1) ◽  
Author(s):  
Priya Bariya ◽  
Linda L. Randall
Keyword(s):  
Lipid Bilayers ◽  
Rate Constant ◽  
Apparent Rate Constant ◽  
Membrane Vesicles ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Secretory System ◽  
Rate Limiting

ABSTRACTIn all cells, a highly conserved channel transports proteins across membranes. InEscherichia coli, that channel is SecYEG. Many investigations of this protein complex have used purified SecYEG reconstituted into proteoliposomes. How faithfully do activities of reconstituted systems reflect the properties of SecYEG in the native membrane environment? We investigated by comparing threein vitrosystems: the native membrane environment of inner membrane vesicles and two methods of reconstitution. One method was the widely used reconstitution of SecYEG alone into lipid bilayers. The other was our method of coassembly of SecYEG with SecA, the ATPase of the translocase. For nine different precursor species we assessed parameters that characterize translocation: maximal amplitude of competent precursor translocated, coupling of energy to transfer, and apparent rate constant. In addition, we investigated translocation in the presence and absence of chaperone SecB. For all nine precursors, SecYEG coassembled with SecA was as active as SecYEG in native membrane for each of the parameters studied. Effects of SecB on transport of precursors faithfully mimicked observations madein vivo. From investigation of the nine different precursors, we conclude that the apparent rate constant, which reflects the step that limits the rate of translocation, is dependent on interactions with the translocon of portions of the precursors other than the leader. In addition, in some cases the rate-limiting step is altered by the presence of SecB. Candidates for the rate-limiting step that are consistent with our data are discussed.IMPORTANCEThis work presents a comprehensive quantification of the parameters of transport by the Sec general secretory system in the threein vitrosystems. The standard reconstitution used by most investigators can be enhanced to yield six times as many active translocons simply by adding SecA to SecYEG during reconstitution. This robust system faithfully reflects the properties of translocation in native membrane vesicles. We have expanded the number of precursors studied to nine. This has allowed us to conclude that the rate constant for translocation varies with precursor species.

THE REACTION BETWEEN METHYL RADICALS AND ISOBUTANE

1961 ◽  
Vol 39 (10) ◽  
pp. 1920-1928 ◽  
Author(s):  
A. R. Blake ◽  
J. F. Henderson ◽  
K. O. Kutschke
Keyword(s):  
Rate Constant ◽  
Apparent Rate Constant ◽  
Methyl Radicals

It has been confirmed that the apparent rate constant for the reaction between methyl radicals, produced by the photolysis of deuterated acetone, and isobutane increases with decreasing isobutane pressure. An explanation is proposed to account for this observation suggesting that the production of methane by disproportionation between methyl and t-butyl radicals was not negligible as has been assumed previously.

An analytical method for determining rate constants using a periodical irradiation technique

1969 ◽  
Vol 47 (24) ◽  
pp. 4531-4535 ◽  
Author(s):  
W. Kawakami ◽  
H. S. Isbin
Keyword(s):  
Rate Constants ◽  
Analytical Method ◽  
Apparent Rate Constant ◽  
Chloral Hydrate ◽  
Life Time ◽  
First Order ◽  
Radical Concentration ◽  
Γ Rays ◽  
The Mean

A new analytical method is presented for the determination of rate constants using a periodical irradiation technique. This method is applicable to reactions which have both a first and a second order termination for the chain radical concentration, and is illustrated for the radiolysis of aqueous solutions of chloral hydrate by 137Cs γ rays. The apparent rate constant of first order termination, and the mean chain life time of the chain radical were determined to be 1.10 s−1, and 0.25 s for 400 rad/min, at 22 °C, respectively.

Measurements of the apparent rate constant for the reaction of iodine monoxide with chlorine monoxide to form iodine atoms

2000 ◽  
Vol 41 (3) ◽  
pp. 313-319 ◽  
Author(s):  
I. K. Larin ◽  
N. A. Messineva ◽  
D. V. Nevozhai ◽  
A. I. Spasskii ◽  
E. M. Trofimova
Keyword(s):  
Rate Constant ◽  
Apparent Rate Constant ◽  
Iodine Monoxide ◽  
Chlorine Monoxide
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