scholarly journals Kinetics of enzyme-catalysed desymmetrisation of prochiral substrates: product enantiomeric excess is not always constant

2021 ◽  
Vol 17 ◽  
pp. 873-884
Author(s):  
Peter J Halling
Keyword(s):  
Enantiomeric Excess ◽  
Major Effect ◽  
High Conversion ◽  
Single Function ◽  
Ping Pong ◽  
Plausible Values ◽  
Kinetic Mechanisms ◽  
Equilibrium Conversion ◽  
Kinetics Of ◽  
Prochiral Ketone

The kinetics of enzymatic desymmetrisation were analysed for the most common kinetic mechanisms: ternary complex ordered (prochiral ketone reduction); ping-pong second (ketone amination, diol esterification, desymmetrisation in the second half reaction); ping-pong first (diol ester hydrolysis) and ping-pong both (prochiral diacids). For plausible values of enzyme kinetic parameters, the product enantiomeric excess (ee) can decline substantially as the reaction proceeds to high conversion. For example, an ee of 0.95 at the start of the reaction can decline to less than 0.5 at 95% of equilibrium conversion, but for different enzyme properties it will remain almost unchanged. For most mechanisms a single function of multiple enzyme rate constants (which can be termed ee decline parameter, eeDP) accounts for the major effect on the tendency for the ee to decline. For some mechanisms, the concentrations or ratios of the starting materials have an important influence on the fall in ee. For the application of enzymatic desymmetrisation it is important to study if and how the product ee declines at high conversion.

scholarly journals Kinetics of Enantiomerically Enriched Synthesis of Solketal Esters Using Native and SBA-15 supported P. Fluorescens Lipase

2017 ◽  
Vol 38 (2) ◽  
pp. 209-215
Author(s):  
Aurelia Zniszczoł ◽  
Katarzyna Szymańska ◽  
Jacek Kocurek ◽  
Jolanta Bryjak ◽  
Krzysztof Walczak ◽  
...  
Keyword(s):  
Enantiomeric Excess ◽  
Product Inhibition ◽  
Acyl Donor ◽  
Vinyl Esters ◽  
Alkaline Lipase ◽  
Ping Pong ◽  
Native Lipase ◽  
Optimized Conditions ◽  
Kinetics Of ◽  
Positive Effect

Abstract The studies showed that alkaline lipase from Pseudomonas fluorescens enables an irreversible transesterification of vinyl esters to give enantiomeric excess (eeR) of about 80% using vinyl butyrate as acyl donor and diisopropyl ether as a solvent, at partially optimized conditions. For the native lipase the process was adequately described by a five-parameter Ping-Pong Bi Bi model for both enantiomers plus expression accounting for the formation of enzyme-acyl donor complex, but for the same lipase supported on mesoporous materials of SBA-15-Oc type, R-product inhibition also had to be taken into account. The use of hydrophobic support increased by more than two-fold the rate of the S-solketal conversion but even more that of R-solketal. Thus the immobilization of lipase had very positive effect on the process kinetics but decreased its enantioselectivity.

scholarly journals Kinetic Analysis of the Hydrolysis of Pentose-1-Phosphates Through Apparent Nucleoside Phosphorolysis Equilibrium Shifts

2020 ◽  
Author(s):  
Felix Kaspar ◽  
Peter Neubauer ◽  
Anke Kurreck
Keyword(s):  
Kinetic Analysis ◽  
Hydrolysis Kinetics ◽  
Equilibrium Thermodynamics ◽  
Apparent Increase ◽  
Equilibrium Conversion ◽  
Sugar Phosphates ◽  
Kinetics Of ◽  
Hydrolysis Of

<div>Ask what an equilibrium can do for you:</div><div>Hydrolysis of pentose-1-phosphates leads to an apparent increase of the equilibrium conversion in nucleoside phosphorolysis reactions. This information can be leveraged via equilibrium thermodynamics to determine the hydrolysis kinetics of in situ generated sugar phosphates, which are known to be elusive and difficult to quantify.<br></div>

Synthesize Phosphomolybdic Acid-Doped Polyaniline Microspheres for Catalytic Applications

2014 ◽  
Vol 484-485 ◽  
pp. 137-140
Author(s):  
Jin Zhang Tao
Keyword(s):  
Hydrogen Peroxide ◽  
Formation Mechanism ◽  
Critical Role ◽  
Phosphomolybdic Acid ◽  
Major Effect ◽  
High Conversion ◽  
Composite Microspheres ◽  
Pani Composite ◽  
Doped Polyaniline ◽  
Catalytic Applications

Polyaniline (PANI) composite have generated great interest in the catalyst field due to the coordinate properties of their component. Herein, PANI-PMo12 composite microspheres were successfully fabricated via a facial oxypolymerization with hydrogen peroxide as oxidant and phosphomolybdic acid (PMo12) as dopant. The PANI-PMo12 microspheres were characterized by SEM, XRD, FTIR and XPS. The concentration of PMo12 had a major effect on the diameter of microsphere. The solvent ethanol also played a critical role in the formation of microspheres. The formation mechanism of the PANI-PMo12 microspheres was proposed. Further, the composite microspheres could be directly used as catalyst and displayed a high conversion and selectivity in the epoxidation of cis-cyclooctene with aqueous H2O2 as an oxidant.

scholarly journals THE TIME OF SYNTHESIS AND THE CONSERVATION OF MITOSIS-RELATED PROTEINS IN CULTURED HUMAN AMNION CELLS

1967 ◽  
Vol 34 (1) ◽  
pp. 97-110 ◽  
Author(s):  
Jesse E. Sisken ◽  
Elaina Wilkes
Keyword(s):  
Time Lapse ◽  
Major Effect ◽  
Human Amnion ◽  
Daughter Cells ◽  
Low Concentrations ◽  
Associated Proteins ◽  
A Cell ◽  
Quantitative Analyses ◽  
Related Proteins ◽  
Kinetics Of

p-Fluorophenylalanine (PFPA), an analogue of phenylalanine which may be incorporated into proteins, increases the duration of mitosis. In the present experiments, based upon quantitative analyses of time-lapse cinemicrographic films, brief treatments of cells with PFPA are shown to affect the duration of metaphase in only those cells which enter division during or shortly after treatment. The offspring of cells with prolonged metaphases also tend to have prolonged metaphases. Analyses of the kinetics of the appearance of prolonged metaphases indicate that some protein specifically associated with mitosis is synthesized primarily during a period which corresponds closely to G2. The manner in which the defect is passed on to daughter cells indicates that the protein involved is conserved and reutilized by daughter cells for their subsequent divisions. Comparable experiments performed with low concentrations of puromycin indicate that the major effect of PFPA is due to its incorporation into protein rather than its ability to inhibit protein synthesis. The fact that puromycin-induced effects can also be passed on to daughter cells is interpreted to mean that cells make only specific amounts of some mitosis-associated proteins and that if a cell "inherits" a deficiency in such protein it is not able to compensate for the deficiency.

Kinetics of Na-Li exchange in high and low K sheep red blood cells

1989 ◽  
Vol 257 (1) ◽  
pp. C58-C64 ◽  
Author(s):  
K. H. Ryu ◽  
N. C. Adragna ◽  
P. K. Lauf
Keyword(s):  
Red Blood Cells ◽  
Blood Cells ◽  
Cell Types ◽  
Sheep Red Blood Cells ◽  
High K ◽  
Ping Pong ◽  
Order Of Magnitude ◽  
Low K ◽  
Kinetics Of ◽  
System Operating

The kinetic parameters and transport mechanism of Na-Li exchange were studied in both low K (LK) and high K (HK) sheep red blood cells with cellular Na [( Na]i) and Li concentrations [( Li]i) adjusted by the nystatin technique (Nature New Biol. 244: 47-49, 1973 and J. Physiol. Lond. 283: 177-196, 1978). Maximum velocities (Vm) for Li fluxes and half-activation constants (K1/2) for Li and Na of the Na-Li exchanger were determined. The K1/2 values for both Li and Na appeared to be similar in both cell types, although they were about two to three times lower on the inside than on the outside of the membrane. Furthermore, the K1/2 values for Li were at least an order of magnitude smaller than those for Na, suggesting substantial affinity differences for these two cations. The Vm values for Li fluxes, on the other hand, appear to be lower in HK than in LK cells. When Na and Li fluxes were measured simultaneously, a trans stimulatory effect by Na on Li fluxes was observed. From measurements of Li influx at different concentrations of external Li and different [Na]i, the ratio of the apparent Vm to the apparent external Li affinity was calculated to be independent of [Na]i for both types of sheep red blood cells. Similar trans effects of external Na were observed on Li efflux at varying [Li]i. These results are expected for a system operating by a “ping-pong” mechanism.

scholarly journals The kinetics of rat liver and heart mitochondrial β-hydroxybutyrate dehydrogenase

1979 ◽  
Vol 179 (3) ◽  
pp. 579-581 ◽  
Author(s):  
G A Tucker ◽  
A P Dawson
Keyword(s):  
Rat Liver ◽  
Rat Heart ◽  
Mitochondrial Membrane ◽  
Liver Mitochondria ◽  
Kinetic Constants ◽  
Kinetic Properties ◽  
Kinetic Mechanisms ◽  
Solubilized Enzyme ◽  
Beta Hydroxybutyrate ◽  
Kinetics Of

The kinetic mechanisms of the beta-hydroxybutyrate dehydrogenase from rat heart and liver mitochondria were investigated. Both enzymes, show an Ordered Bi Bi mechanism and there are no major differences in the kinetic constants. In both cases, the solubilized enzyme, re-activated with phosphatidylcholine, shows kinetic properties very similar to those of the enzyme bound to the mitochondrial membrane.

scholarly journals Mechanism of the 2,3-diphosphoglycerate-dependent phosphoglycerate mutase from rabbit muscle

1972 ◽  
Vol 130 (2) ◽  
pp. 397-410 ◽  
Author(s):  
H. G. Britton ◽  
J. B. Clarke
Keyword(s):  
Chemical Equilibrium ◽  
Phosphoglycerate Mutase ◽  
Rabbit Muscle ◽  
Kinetic Measurements ◽  
Rate Limiting Step ◽  
Ping Pong ◽  
Sequential Mechanism ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Intramolecular Transfer

1. The properties and kinetics of the 2,3-diphosphoglycerate-dependent phosphoglycerate mutases are discussed. There are at least three possible mechanisms for the reaction: (i) a phosphoenzyme (Ping Pong) mechanism; (ii) an intermolecular transfer of phosphate from 2,3-diphosphoglycerate to the substrates (sequential mechanism); (iii) an intramolecular transfer of phosphate. It is concluded that these mechanisms cannot be distinguished by conventional kinetic measurements. 2. The fluxes for the different mechanisms are calculated and it is shown that it should be possible to distinguish between the mechanisms by appropriate induced-transport tests and by comparing the fluxes of 32P- and 14C-labelled substrates at chemical equilibrium. 3. With 14C-labelled substrates no induced transport was found over a wide concentration range, and with 32P-labelled substrates co-transport occurred that was independent of concentration over a twofold range. 14C-labelled substrates exchange at twice the rate of 32P-labelled substrates at chemical equilibrium. The results were completely in accord with a phosphoenzyme mechanism and indicated a rate constant for the isomerization of the phosphoenzyme of not less than 4×106s−1. The intramolecular transfer of phosphate (and intermolecular transfer between two or more molecules of substrate) were completely excluded. The intermolecular transfer of phosphate from 2,3-diphosphoglycerate would have been compatible with the results only if the Km for 2-phosphoglycerate had been over 7.5-fold smaller than the observed value and if an isomerization of the enzyme-2,3-diphosphoglycerate complex had been the major rate-limiting step in the reaction. 4. The very rapid isomerization of the phosphoenzyme that the experiments demonstrate suggests a mechanism that does not involve a formal isomerization. According to this new scheme the enzyme is closely related mechanistically and perhaps evolutionarily to a 2,3-diphosphoglycerate diphosphatase.

scholarly journals Kinetics and mechanisms of catalyzed dual-E (antithetic) controllers

2021 ◽  
Author(s):  
Qaiser Waheed ◽  
Huimin Zhou ◽  
Peter Ruoff
Keyword(s):  
Ternary Complex ◽  
Reaction Kinetic ◽  
Zero Order ◽  
Control Engineering ◽  
Environmental Disturbances ◽  
Integral Control ◽  
Analysis And Design ◽  
Zero Order Kinetics ◽  
Ping Pong ◽  
Kinetic Mechanisms

Homeostasis plays a central role in our understanding how cells and organisms are able to oppose environmental disturbances and thereby maintain an internal stability. During the last two decades there has been an increased interest in using control engineering methods, especially integral control, in the analysis and design of homeostatic networks. Several reaction kinetic mechanisms have been discovered which lead to integral control. In two of them integral control is achieved, either by the removal of a single control species E by zero-order  kinetics ("single-E controllers"), or by the removal of two control species  by second-order kinetics ("antithetic or dual-E control"). In this paper we show results when the control species E 1  and E 2  in antithetic control are removed enzymatically by ping-pong or ternary-complex mechanisms. Our findings show that enzyme-catalyzed dual-E controllers can work in two control modes. In one mode, one of the two control species is active, but requires zero-order kinetics in its removal. In the other mode, both controller species are active and both are removed enzymatically. Conditions for the two control modes are put forward and biochemical examples with the structure of enzyme-catalyzed dual-E controllers are discussed.

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