scholarly journals The catalase–hydrogen peroxide system. Kinetics of catalatic action at high substrate concentrations

1968 ◽  
Vol 110 (4) ◽  
pp. 617-620 ◽  
Author(s):  
Peter Jones ◽  
A. Suggett
Keyword(s):  
Hydrogen Peroxide ◽  
Reaction Time ◽  
Time Effect ◽  
Time Dependent ◽  
Inhibitory Effects ◽  
Michaelis Constant ◽  
High Substrate ◽  
Compound Ii ◽  
Kinetics Of ◽  
Substrate Concentrations

1. A re-examination of the catalase–hydrogen peroxide reaction at high substrate concentrations, by using the quenched-flow technique, reveals a more complex kinetic behaviour than that previously reported. At constant reaction time the catalatic process obeys Michaelis–Menten kinetics, but the apparent Michaelis constant is markedly time-dependent, whereas the conventional catalase activity is independent of time. 2. The kinetics of the ‘time effect’ were analysed and it is suggested that the effect derives from the formation of an inactive species (thought to be catalase Compound II). The process shows Michaelis–Menten kinetics, with a Michaelis constant equal to that for the catalatic reaction in the limit of zero reaction time. 3. It has been confirmed that certain buffer components have marked inhibitory effects on the catalatic reaction and that, in unbuffered systems, catalatic activity is substantially independent of pH in the range 4·7–10·5.

Kinetic laws for solid-supported enzymes

1970 ◽  
Vol 48 (10) ◽  
pp. 1498-1504 ◽  
Author(s):  
P. V. Sundaram ◽  
A. Tweedale ◽  
K. J. Laidler
Keyword(s):  
Substrate Concentration ◽  
Free Solution ◽  
Kinetic Behavior ◽  
Michaelis Constant ◽  
Solid Supports ◽  
High Substrate ◽  
Substrate Concentrations

Enzymes behave differently when attached to solid supports for four main reasons: (1) their conformations when they are supported may differ from those in free solution, (2) they act upon substrates in a different environment, (3) there will be partitioning of substrate between the support and the free solution, and (4) there will be effects due to diffusion of the substrate in the support. The present paper examines effects (3) and (4) and shows how rates will vary with substrate concentration. If factors (1) and (2) do not enter, rates in the limit of high substrate concentrations will be the same for the supported enzyme as in free solution. At low substrate concentrations, rates will be less for the supported enzyme if the substrate is less soluble in the support than in free solution, and the apparent Michaelis constant, Km(app.), will be greater; conversely, for higher solubility in the support, rates will be greater and Km(app.) smaller. Effect (4) leads to lower rates and higher Km(app.) values, except in the limit of high substrate concentrations. At a sufficiently low thickness of the support, depending upon the activity of the enzyme, the kinetic behavior becomes identical with that in free solution.

Flow kinetics of immobilized β-glucosidase

1986 ◽  
Vol 64 (2) ◽  
pp. 139-145 ◽  
Author(s):  
Yuchiong Hsuanyu ◽  
Keith J. Laidler
Keyword(s):  
Ph Dependence ◽  
Kinetic Studies ◽  
Free Enzyme ◽  
Diffusion Control ◽  
Michaelis Constant ◽  
Ph Optimum ◽  
Ph Values ◽  
Nylon Tubing ◽  
Kinetics Of ◽  
Substrate Concentrations

The enzyme β-glucosidase was attached covalently to the inner surface of nylon tubing. Flow kinetic studies were carried out at a range of temperatures, pH values, flow rates, and substrate concentrations. Various tests showed that the extent of diffusion control was negligible. At 25 °C the Michaelis constant was 33.4 mM, not greatly different from the value for the enzyme in free solution. The pH dependence was similar to that for the free enzyme. The Arrhenius plots showed inflexions at about 22 °C, as with the free enzyme, the changes in slope being small at the pH optimum of about 5.9 and becoming much more pronounced as the pH is increased or decreased. The immobilized enzyme is more stable than the free enzyme, both on storage at low and higher temperatures, and its reuse stability is greater.

Horse serum butyrylcholinesterase kinetics: a molecular mechanism based on inhibition studies with dansylaminoethyltrimethylammonium

1987 ◽  
Vol 65 (6) ◽  
pp. 529-535 ◽  
Author(s):  
Gilles Cauet ◽  
Alain Friboulet ◽  
Daniel Thomas
Keyword(s):  
Horse Serum ◽  
Reversible Inhibitor ◽  
Substrate Molecule ◽  
High Substrate ◽  
Peripheral Site ◽  
Inhibition Studies ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Substrate Concentrations ◽  
Enzyme Intermediate

The kinetics of the hydrolysis of butyrylthiocholine by horse serum butyrylcholinesterase (acylcholine acylhydrolase; BuChE; EC 3.1.1.8) exhibit an activation phenomenon at high substrate concentrations. At least two mechanistic models can account for the enzyme kinetics: one assumes the binding of an additional substrate molecule on the acyl–enzyme intermediate, and the other hypothesizes the existence of a peripheral regulatory site for the substrate. (1-Dimethylaminonaphthalene-5-sulfonamidoethyl)-trimethylammonium perchlorate, a potent reversible inhibitor, appears to affect BuChE activity by binding to a peripheral site. The inhibition is of the mixed type at low substrate concentrations and of the competitive type at high substrate concentrations. This is consistent with a peripheral site for the binding of the substrate responsible for the activation phenomenon.

Inhibition Kinetics of Polyphenol Oxidase from Purple Sweet Potato by Ascorbic Acid

2013 ◽  
Vol 333-335 ◽  
pp. 1921-1925
Author(s):  
Lu Gao ◽  
Ke Da Li ◽  
Ying Chang Li
Keyword(s):  
Ascorbic Acid ◽  
Sweet Potato ◽  
Polyphenol Oxidase ◽  
Substrate Inhibition ◽  
Competitive Inhibitor ◽  
Inhibitory Effects ◽  
Michaelis Constant ◽  
Maximum Reaction ◽  
Purple Sweet Potato ◽  
Kinetics Of

With catechol as a substrate, some kinetic parameters, including Michaelis constant (Km), maximum reaction velocity (Vmax) and substrate inhibition constant (KI) for the reaction catalyzed by polyphenol oxidase (PPO) from purple sweet potato (PSP) were mainly studied here by spectrophotometry. Kmand Vmaxwere determined depending on bi-reciprocal diagram of Lineweaver-Burk and Hanes-Woolf diagram respectively, with Kmof 12.06 mM and Vmaxof 43.66 mM·min. The effects of four various inhibitors on PPO activity were different. Ascorbic acid (AA) and phytic acid (PA) showed strong inhibitory effects, with AA of the highest effect and citric acid (CA) the lowest. Among these inhibitors, AA was a reversible competitive inhibitor with KIof 15.26 mM, which was significant and instructive to the quality and benefit improvement of processed PSP products.

scholarly journals In vivo analysis of the size- and time-dependent uptake of NaYF4:Yb,Er upconversion nanocrystals by pumpkin seedlings

2015 ◽  
Vol 3 (1) ◽  
pp. 144-150 ◽  
Author(s):  
J. Nordmann ◽  
S. Buczka ◽  
B. Voss ◽  
M. Haase ◽  
K. Mummenhoff
Keyword(s):  
Time Dependent ◽  
Upconversion Nanocrystals ◽  
In Vivo Analysis ◽  
Kinetics Of

We have investigated the kinetics of the uptake and the translocation of nanoparticles of different size in plants.

Kinetics of hydrogen peroxide-sulfur(IV) reaction in rainwater collected at a northeastern U.S. site

1986 ◽  
Vol 91 (D12) ◽  
pp. 13264 ◽  
Author(s):  
Y.-N. Lee ◽  
J. Shen ◽  
P. J. Klotz ◽  
S. E. Schwartz ◽  
L. Newman
Keyword(s):  
Hydrogen Peroxide ◽  
Kinetics Of

scholarly journals Determinants of mRNA stability in Dictyostelium discoideum amoebae: differences in poly(A) tail length, ribosome loading, and mRNA size cannot account for the heterogeneity of mRNA decay rates.

1988 ◽  
Vol 8 (5) ◽  
pp. 1957-1969 ◽  
Author(s):  
R A Shapiro ◽  
D Herrick ◽  
R E Manrow ◽  
D Blinder ◽  
A Jacobson
Keyword(s):  
Steady State ◽  
Dictyostelium Discoideum ◽  
Mrna Decay ◽  
Decay Rates ◽  
Time Dependent ◽  
Translational Efficiency ◽  
Cdna Clones ◽  
Dependent Manner ◽  
Significant Difference ◽  
Kinetics Of

As an approach to understanding the structures and mechanisms which determine mRNA decay rates, we have cloned and begun to characterize cDNAs which encode mRNAs representative of the stability extremes in the poly(A)+ RNA population of Dictyostelium discoideum amoebae. The cDNA clones were identified in a screening procedure which was based on the occurrence of poly(A) shortening during mRNA aging. mRNA half-lives were determined by hybridization of poly(A)+ RNA, isolated from cells labeled in a 32PO4 pulse-chase, to dots of excess cloned DNA. Individual mRNAs decayed with unique first-order decay rates ranging from 0.9 to 9.6 h, indicating that the complex decay kinetics of total poly(A)+ RNA in D. discoideum amoebae reflect the sum of the decay rates of individual mRNAs. Using specific probes derived from these cDNA clones, we have compared the sizes, extents of ribosome loading, and poly(A) tail lengths of stable, moderately stable, and unstable mRNAs. We found (i) no correlation between mRNA size and decay rate; (ii) no significant difference in the number of ribosomes per unit length of stable versus unstable mRNAs, and (iii) a general inverse relationship between mRNA decay rates and poly(A) tail lengths. Collectively, these observations indicate that mRNA decay in D. discoideum amoebae cannot be explained in terms of random nucleolytic events. The possibility that specific 3'-structural determinants can confer mRNA instability is suggested by a comparison of the labeling and turnover kinetics of different actin mRNAs. A correlation was observed between the steady-state percentage of a given mRNA found in polysomes and its degree of instability; i.e., unstable mRNAs were more efficiently recruited into polysomes than stable mRNAs. Since stable mRNAs are, on average, "older" than unstable mRNAs, this correlation may reflect a translational role for mRNA modifications that change in a time-dependent manner. Our previous studies have demonstrated both a time-dependent shortening and a possible translational role for the 3' poly(A) tracts of mRNA. We suggest, therefore, that the observed differences in the translational efficiency of stable and unstable mRNAs may, in part, be attributable to differences in steady-state poly(A) tail lengths.

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