The determination of the rate-limiting step in a proton transfer reaction from the breakdown of the Swain-Schaad relation

1977 ◽  
Vol 99 (2) ◽  
pp. 637-638 ◽  
Author(s):  
W. J. Albery ◽  
Jeremy R. Knowles
Keyword(s):  
Proton Transfer ◽  
Transfer Reaction ◽  
Proton Transfer Reaction ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

scholarly journals Influence of the position of the double bond in steroid substrates on the efficiency of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Δ4–Δ5-isomerase

1980 ◽  
Vol 185 (3) ◽  
pp. 723-732 ◽  
Author(s):  
Hadassa Weintraub ◽  
Etienne-Emile Baulieu ◽  
Annette Alfsen
Keyword(s):  
Double Bond ◽  
Proton Transfer ◽  
Transfer Reaction ◽  
Proton Transfer Reaction ◽  
Process Data ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Isomerization Process ◽  
Rate Limiting ◽  
Pseudomonas Testosteroni

Studies of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Δ4–Δ5-isomerase with Δ5(6)- and Δ5(10)-steroid substrates demonstrate the importance of the position of the double bond for the efficiency of the isomerization process. Thus 3-oxo-Δ5(6)-substrates have markedly high kcat. values, whereas those of 3-oxo-Δ5(10)-substrates are very low and their apparent Km values approach equilibrium dissociation constants. The first step in the isomerization process is: [Formula: see text] which is governed by the k−1/k+1 ratio and is shown to be very similar for the two classes of substrates (3-oxo-Δ5(6)- and -Δ5(10)-steroids). They therefore differ in the steps distal to the initial formation of the Michaelis–Menten complex. The use of the deuterated androst-5(6)-ene-3,17-dione substrate enabled us to calculate individual rate constants k+1 and k−1 as well as to determine the apparent rate-limiting step in the isomerization process. With the deuterated oestr-5(10)-ene-3,17-dione substrate, no significant isotope effect was observed suggesting that a different rate-limiting step may be operative in this isomerization process. Data are presented that indicate that under optimal concentrations of the efficient androst-5(6)-ene-3,17-dione substrate, the forward reaction for ES complex formation (as defined by k+1) is limited only by diffusion and the apparent Km does not approach the equilibrium constant, suggesting that the evolution of this enzyme has proceeded close to ‘catalytic perfection’.

scholarly journals Correction: The applicability of proton transfer reaction-mass spectrometry (PTR-MS) for determination of isocyanic acid (ICA) in work room atmospheres

2018 ◽  
Vol 20 (2) ◽  
pp. 415-415
Author(s):  
Mikolaj Jan Jankowski ◽  
Raymond Olsen ◽  
Claus Jørgen Nielsen ◽  
Yngvar Thomassen ◽  
Paal Molander
Keyword(s):  
Mass Spectrometry ◽  
Proton Transfer ◽  
Transfer Reaction ◽  
Proton Transfer Reaction ◽  
Reaction Mass ◽  
Isocyanic Acid

Correction for ‘The applicability of proton transfer reaction-mass spectrometry (PTR-MS) for determination of isocyanic acid (ICA) in work room atmospheres’ by Mikolaj Jan Jankowski et al., Environ. Sci.: Processes Impacts, 2014, 16, 2423–2431.

scholarly journals Atomically manipulated proton transfer energizes water oxidation on silicon carbide photoanodes

2018 ◽  
Vol 6 (47) ◽  
pp. 24358-24366 ◽  
Author(s):  
Hao Li ◽  
Huan Shang ◽  
Yuchen Shi ◽  
Rositsa Yakimova ◽  
Mikael Syväjärvi ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Electron Transfer ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Proton Coupled Electron Transfer ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Preferential exposure of Si-face of SiC will mechanistically shift the rate limiting step of water oxidation from sluggish proton-coupled electron transfer on C-face to a more energy-favorable electron transfer.

scholarly journals DETERMINATION OF l-HISTIDINE IN NANOGRAM AMOUNTS AND THE QUESTION OF ITS OCCURRENCE IN MAST CELLS

1972 ◽  
Vol 20 (11) ◽  
pp. 917-922 ◽  
Author(s):  
DAVID I. WILKINSON ◽  
DAVID GLICK
Keyword(s):  
Mast Cells ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Peritoneal Mast Cells ◽  
Before And After ◽  
Chromatographic Detection ◽  
Rat Peritoneal Mast Cells ◽  
Rate Limiting

In an attempt to clarify the question of whether histidine is stored in the mast cell for coversion to histamine or whether the rate of conversion is rapid enough to prevent accumulation of histidine so that the rate-limiting step is the histidine uptake, it was found that no histidine was demonstrable in rat peritoneal mast cells by either quantitative analysis or paper chromatographic detection. Microadaptation of Hassall's method, based on conversion of l-histidine by histidase to urocanic acid and measurement of the latter by its absorbance at 277 nm, was made to permit determination of histidine in nanogram amounts in the presence of histamine. This adaptation was found reliable when compared with the o-phthalaldehyde method in estimation of l-histidine in serum and in insulin hydrolysate, and then it was applied to analysis of mast cells before and after l-histidine uptake in vitro. The adaptation should be generally useful in microanalysis of l-histidine in histologically and cytologically defined samples.

The applicability of proton transfer reaction-mass spectrometry (PTR-MS) for determination of isocyanic acid (ICA) in work room atmospheres

2014 ◽  
Vol 16 (10) ◽  
pp. 2423-2431 ◽  
Author(s):  
Mikolaj Jan Jankowski ◽  
Raymond Olsen ◽  
Claus Jørgen Nielsen ◽  
Yngvar Thomassen ◽  
Paal Molander
Keyword(s):  
Mass Spectrometry ◽  
Proton Transfer ◽  
Real Time ◽  
Mass Spectrometer ◽  
Transfer Reaction ◽  
Proton Transfer Reaction ◽  
Reaction Mass ◽  
Isocyanic Acid

This study presents a real-time method to quantitatively determine isocyanic acid (ICA) in workroom air using a proton transfer reaction-mass spectrometer (PTR-MS).

Base-catalyzed formation of spiro adduct from N-methyl-N-(2,4,6-trinitrophenyl)glycinamide, the smiles rearrangement of the amide in methanol

1988 ◽  
Vol 53 (3) ◽  
pp. 601-618 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Makky M. M. Hassanien ◽  
Vojeslav Štěrba
Keyword(s):  
Proton Transfer ◽  
Equilibrium Constant ◽  
Ammonium Salt ◽  
Aliphatic Amine ◽  
Reaction Pathway ◽  
Smiles Rearrangement ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Kinetics Of

The reaction of N-methyl-N-(2,4,6-trinitrophenyl)glycinamide (Ic with methoxide in methanol produces the spiro adduct IIc(A). In methanolic acetate buffers, the equilibrium is rapidly established between the spiro adduct IIc(A) and the dipolar ion of 2-methylamino-N-(2,4,6-trinitrophenyl)acetamide (IIIc(Z)). The equilibrium constant of the reaction IIIc(Z) ⇆ IIc(A) + H+ is by eight orders of magnitude greater than that of the analogous cyclization of 2-methylamino-N-methyl-N-(2,4,6-trinitrophenyl)acetamide to the spiro adduct. In chloracetate buffers, the dipolar ion is protonated to give 2-methylammonium-N-(2,4,6-trinitrohenyl)acetamide IIIc(K). The kinetics of the reversible reaction IIIc(Z) ⇆ IIc(A) + H+ has been studied in acetate buffers, aliphatic amine – ammonium salt buffers, and methoxide solutions. In all cases, the rate-limiting step was the proton transfer with half-lives in milliseconds. In more basic methanolic buffers (pH > 10) the rate-limiting step consists in the formation of spiro adduct from the zwiterion IIIc(Z) resulting from the protonation of the anion IIIc(A). n acetate buffers, the second reaction pathway via the cation IIIc(K) is predominant.

Determination of the Isotope Effect of the Enzymatic Oxidation of (R)Carnitine by Displacement of the Equilibrium via Mass Action

1975 ◽  
Vol 30 (7-8) ◽  
pp. 438-441
Author(s):  
Klaus Brendel ◽  
Rubin Bressler ◽  
Miguel A. Alizade
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Isotope Effect ◽  
Mass Action ◽  
Enzymatic Oxidation ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Different Temperatures ◽  
Acid Hydrochloride ◽  
Rate Limiting

Abstract An isotope effect of the dehydrogenation of (R) Carnitine [(R) 3-hydroxy-4-trimethylamino-butyric acid hydrochloride] catalyzed by (R) carnitine dehydrogenase [(R) carnitine: NAD oxido-reductase E.C. 1.1.1.108] from Pseudomonas aeruginosa was measured at different temperatures. It was found that k1H/k3H does not vary greatly with changes of temperature. The value of 3 for k1H/k3H measured at small initial conversions strongly indicated that the rate limiting step of the oxidation of (R) carnitine is the cleavage of the C-H bond at C3.

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