Distinguishing Rate-Limiting Electron versus H-Atom Transfers in Cu2(O2)-Mediated OxidativeN-Dealkylations:  Application of Inter- versus Intramolecular Kinetic Isotope Effects

2003 ◽  
Vol 125 (42) ◽  
pp. 12670-12671 ◽  
Author(s):  
Jason Shearer ◽  
Christiana Xin Zhang ◽  
Lanying Q. Hatcher ◽  
Kenneth D. Karlin
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Rate Limiting

scholarly journals Kinetic isotope effects of peptidylglycine α-hydroxylating mono-oxygenase reaction

1998 ◽  
Vol 336 (1) ◽  
pp. 131-137 ◽  
Author(s):  
Kenichi TAKAHASHI ◽  
Tetsuo ONAMI ◽  
Masato NOGUCHI
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Tracer Method ◽  
Deuterium Isotope Effect ◽  
Critical Determinant ◽  
Product Release ◽  
Kinetic Isotope ◽  
Hydroxylation Reaction ◽  
Double Label ◽  
Rate Limiting

Many bioactive polypeptides or neuropeptides possess a C-terminal α-amide group as a critical determinant for their optimal bioactivities. The amide functions are introduced by the sequential actions of peptidylglycine α-hydroxylating mono-oxygenase (PHM; EC 1.14.17.3) and peptidylamidoglycollate lyase (PAL; EC 4.3.2.5) from their glycine-extended precursors. In the present study we examined the kinetic isotope effects of the frog PHM reaction by competitive and non-competitive approaches. In the competitive approach we employed the double-label tracer method with d-Tyr-[U-14C]Val-Gly, d-Tyr-[3,4-3H]Val-[2,2-2H2]-Gly, and d-Tyr-Val-(R,S)[2-3H]Gly as substrates, and we determined the deuterium and tritium effects on Vmax/Km as 1.625±0.041 (mean±S.D.) and 2.71±0.16 (mean±S.D.), respectively. The intrinsic deuterium isotope effect (Dk) on the glycine hydroxylation reaction was estimated to be 6.5–10.0 (mean 8.1) by the method of Northrop [Northrop (1975) Biochemistry 14, 2644–2651]. In the non-competitive approach with N,N-dimethyl-1,4-phenylenediamine as a reductant, however, the deuterium effect on Vmax (DV) was approximately unity, although the deuterium effect on Vmax/Km (DV/K) was comparable to that obtained by the competitive approach. These results indicated that DV was completely masked by the presence of one or more steps much slower than the glycine hydroxylation step and that DV/K was diminished from Dk by a large forward commitment to catalysis. The addition of PAL, however, increased the apparent DV from 1.0 to 1.2, implying that the product release step was greatly accelerated by PAL. These results suggest that the product release is rate-limiting in the overall PHM reaction. The large Dk indicated that the glycine hydroxylation catalysed by PHM might proceed in a stepwise mechanism similar to that proposed for the dopamine β-hydroxylase reaction [Miller and Klinman (1983) Biochemistry 22, 3091–3096].

Experimental and Theoretical Kinetic Isotope Effects for Asymmetric Dihydroxylation. Evidence Supporting a Rate-Limiting “(3 + 2)” Cycloaddition

1997 ◽  
Vol 119 (41) ◽  
pp. 9907-9908 ◽  
Author(s):  
Albert J. DelMonte ◽  
Jan Haller ◽  
K. N. Houk ◽  
K. Barry Sharpless ◽  
Daniel A. Singleton ◽  
...  
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Asymmetric Dihydroxylation ◽  
Kinetic Isotope ◽  
Rate Limiting

scholarly journals Comment on “Topography of the free energy landscape of Claisen–Schmidt condensation: solvent and temperature effects on the rate-controlling step” by N. D. Coutinho, H. G. Machado, V. H. Carvalho-Silva and W. A. da Silva, Phys. Chem. Chem. Phys., 2021, 23, 6738

2021 ◽  
Vol 23 (38) ◽  
pp. 22199-22201
Author(s):  
Charles L. Perrin
Keyword(s):  
Temperature Effects ◽  
Isotope Effects ◽  
Energy Landscape ◽  
Kinetic Isotope Effects ◽  
Chem Phys ◽  
Kinetic Isotope ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Rate Controlling Step

The referenced article in PCCP presents calculations of solvent kinetic isotope effects that indicate that the rate-limiting step in base-catalyzed chalcone formation in aqueous solution becomes the second enolization.

scholarly journals Use of pH and Kinetic Isotope Effects To Establish Chemistry as Rate-Limiting in Oxidation of a Peptide Substrate by LSD1

Biochemistry ◽  
2009 ◽  
Vol 48 (23) ◽  
pp. 5440-5445 ◽  
Author(s):  
Helena Gaweska ◽  
Michelle Henderson Pozzi ◽  
Dawn M. Z. Schmidt ◽  
Dewey G. McCafferty ◽  
Paul F. Fitzpatrick
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Peptide Substrate ◽  
Kinetic Isotope ◽  
Rate Limiting

scholarly journals The effect of glycerol on the activity of β-glucosidase from Botryodiplodia theobromae Pat

1988 ◽  
Vol 254 (1) ◽  
pp. 73-76 ◽  
Author(s):  
G M Umezurike
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Rate Equations ◽  
Glycerol Concentration ◽  
Large Excess ◽  
Reaction Sequence ◽  
Botryodiplodia Theobromae ◽  
Kinetic Isotope ◽  
Beta Glucosidase ◽  
Rate Limiting

1. In the activity of the high-Mr beta-glucosidase A (beta-D-glucoside glucohydrolase, EC 3.2.1.21) obtained from culture filtrates of Botryodiplodia theobromae Pat. on o-nitrophenyl beta-D-glucopyranoside as substrate, both Vmax. and Km increased non-linearly with increasing concentration of glycerol, and the Vmax./Km(app.) ratio decreased non-linearly with increasing concentration of glycerol. 2. No increase in rate was observed with phenyl beta-D-glucopyranoside as substrate in the presence of up to 250 mM-glycerol, indicating that glucosylation is rate-limiting with this substrate. 3. With o-nitrophenyl beta-D-glucopyranoside, p-nitrophenyl beta-D-glucopyranoside and phenyl beta-D-glucopyranoside as substrates, kappa cat. values of 793.7 s-1, 62.8 s-1 and 5.4 s-1 respectively were calculated. 4. With o-nitrophenyl beta-D-glucopyranoside and phenyl beta-D-glucopyranoside as substrate, alpha-deuterium kinetic isotope effects of 1.9 +/- 0.03 and 1.01 +/- 0.01 respectively were found; in the presence of 200 mM-glycerol the values were 1.21 +/- 0.03 and 1.02 +/- 0.01 respectively. 5. In the presence of a large excess of o-nitrophenyl beta-D-glucopyranoside [(S] = 35.7 Km), the amount of o-nitrophenol and also of the transglucosylation product formed by beta-glucosidase action increased non-linearly, whereas that of glucose formed decreased non-linearly with increasing glycerol concentration. 6. All these results were found to fit the data calculated from rate equations derived on the basis of the proposed mechanism of enzyme action involving two ion-pair intermediates and a covalent alpha-D-glucosyl-enzyme in the reaction sequence [Umezurike (1987) Biochem. J. 241, 455-462].

scholarly journals Kinetics and mechanism of the anilinolysis of aryl phenyl isothiocyanophosphates in acetonitrile

2013 ◽  
Vol 9 ◽  
pp. 615-620 ◽  
Author(s):  
Hasi Rani Barai ◽  
Hai Whang Lee
Keyword(s):  
Isotope Effects ◽  
Bond Formation ◽  
Kinetic Studies ◽  
Kinetic Isotope Effects ◽  
Bond Breaking ◽  
Stepwise Mechanism ◽  
Kinetic Isotope ◽  
Energy Relationships ◽  
Break Region ◽  
Rate Limiting

Kinetic studies on the reactions of Y-aryl phenyl isothiocyanophosphates with substituted X-anilines and deuterated X-anilines were carried out in acetonitrile at 55.0 °C. The free-energy relationships with X in the nucleophiles were biphasic concave upwards with a break region between X = H and 4-Cl, giving unusual positive ρX and negative βX values with less basic anilines (X = 4-Cl and 3-Cl). A stepwise mechanism with rate-limiting bond breaking for more basic anilines and with rate-limiting bond formation for less basic anilines is proposed based on the positive and negative ρXY values, respectively. The deuterium kinetic isotope effects involving deuterated anilines (XC6H4ND2) showed primary normal and secondary inverse DKIEs for more basic and less basic anilines, rationalized by frontside attack involving hydrogen-bonded four-center-type TSf and backside attack TSb, respectively. The positive ρX values with less basic anilines are substantiated by the tight TS, in which the extent of the bond formation is great and the degree of the bond breaking is considerably small.

Kinetic Isotope Effects on the Rate-Limiting Step of Heme Oxygenase Catalysis Indicate Concerted Proton Transfer/Heme Hydroxylation

2003 ◽  
Vol 125 (52) ◽  
pp. 16208-16209 ◽  
Author(s):  
Roman Davydov ◽  
Toshitaka Matsui ◽  
Hiroshi Fujii ◽  
Masao Ikeda-Saito ◽  
Brian M. Hoffman
Keyword(s):  
Proton Transfer ◽  
Heme Oxygenase ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting
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