Kinetic behaviour of vertebrate hexokinases with emphasis on hexokinase D (IV)

1997 ◽  
Vol 25 (1) ◽  
pp. 131-135 ◽  
Author(s):  
M. L. Cárdenas
Keyword(s):  
Kinetic Behaviour

Light-Induced Metastable Defects in a-Si:H: Towards an Understanding

1985 ◽  
Vol 49 ◽  
Author(s):  
Martin Stutzmann ◽  
Warren B. Jackson ◽  
Chuang Chuang Tsai
Keyword(s):  
Amorphous Silicon ◽  
Mechanical Stress ◽  
Hydrogenated Amorphous Silicon ◽  
Material Parameters ◽  
Kinetic Behaviour ◽  
Proposed Model ◽  
Special Cases ◽  
The Stability ◽  
Hydrogenated Amorphous

AbstractThe dependence of the creation and the annealing of metastable dangling bonds in hydrogenated amorphous silicon on various material parameters will be discussed in the context of a recently proposed model. After a brief review of the kinetic behaviour governing defect creation and annealing in undoped a- Si:H, a number of special cases will be analyzed: the influence of alloying with O, N, C, and Ge, changes introduced by doping and compensation, and the role of mechanical stress. Finally, possibilities to increase the stability of a-Si:H based devices will be examined.

scholarly journals Rates of reactions catalysed by a dimeric enzyme. Effects of the reaction scheme and the kinetic parameters on co-operativity

1991 ◽  
Vol 280 (1) ◽  
pp. 131-137 ◽  
Author(s):  
H Ishikawa ◽  
H Ogino ◽  
H Oshida
Keyword(s):  
Substrate Inhibition ◽  
Reaction Scheme ◽  
Rate Equations ◽  
Kinetic Behaviour ◽  
Hill Coefficients ◽  
S Curve ◽  
Almost All ◽  
The Hill ◽  
Rate Behaviour ◽  
Reaction Schemes

For the reaction S in equilibrium P catalysed by a dimeric enzyme, the reaction schemes are considered on the basis of the KNF model. For each of the ten possible schemes, the rate equation is derived on the basis of the combined steady-state and rapid-equilibrium assumptions. The curves of the plots of initial velocity v versus the substrate concentration [S] and the Hill coefficients h calculated from the rate equations depend strongly on the reaction scheme and the parameter X1. This parameter is defined by log (KS2/KS1) and is a measure of the relative affinities of the first and second protomers for the substrate. When X1 less than 0, v-[S] curves for some schemes exhibit negative co-operativity (h less than 1.0) and v-[S] curves for other schemes are similar to that of the Michaelis-Menten scheme, indicating that, even if there is interaction between the distinct protomers, sigmoidal rate behaviour is not necessarily observed. When X1 greater than 0, all the reaction schemes except one, which shows substrate-inhibition kinetic behaviour, exhibit sigmoidal kinetic behaviour (h greater than 1.0), and at the limit of X1 much greater than 0 the Hill coefficients attain the maximum possible value of 2.0. Furthermore, we have found that, even if X1 = 0, the v-[S] curve for almost all the schemes considered in the present work does not necessarily agree with that for the Michaelis-Menten scheme. This means that the deviation of the v-[S] curve from a hyperbola can be observed even if there is no interaction between the distinct protomers.

Anti-TSH receptor antibodies in Graves' disease modulate the kinetic behaviour of autologous thyroid TSH receptors. Evidence of the IgG-induced cross-linkage of autologous TSH receptors

1984 ◽  
Vol 105 (3) ◽  
pp. 330-340 ◽  
Author(s):  
Tjerk W. A. de Bruin ◽  
Daan van der Heide ◽  
Maria C. Krol
Keyword(s):  
Binding Sites ◽  
Plasma Membranes ◽  
Tsh Receptor ◽  
Human Thyroid ◽  
Graves Disease ◽  
Kinetic Behaviour ◽  
High Affinity ◽  
Cross Linkage ◽  
Receptor Antibodies ◽  
Tsh Receptor Antibodies

Abstract. The effect of the anti-TSH receptor antibodies present in the sera of 8 patients with Graves' disease on the affinity constant (Ka) and the number (R) of TSH receptors in autologous human thyroid plasma membranes was investigated. Kinetic analysis of [125I]bTSH binding to human thyroid plasma membranes in the presence of autologous Graves' and normal gammaglobulins was carried out by means of a computer fitting programme. Analysis of the TSH-TSH receptor interaction in the presence of TSH alone yielded curvilinear Scatchard plots, indicating the existence of two independent classes of binding sites (high affinity Ka: 8.5 ± 4.8 × 108 m−1; low affinity Ka: 5.3 ± 2.7 × 106 m−1). Similarly the Scatchard plot for this interaction in the presence of normal gammaglobulins is also curvilinear. Linear Scatchard plots, indicating the existence of only one class of high affinity TSH binding sites (Ka: 3.5 ± 1.8 × 108 m−1), were obtained for both autologous gammaglobulins and pure IgG from 8 patients with Graves' disease. The number of high affinity TSH binding sites in the presence of Graves' gammaglobulins had increased on the average by a factor 3.76 ± 0.74 (sd) with respect to the number found in the presence of normal gammaglobulins. This marked change in the kinetic behaviour of the TSH binding sites provided evidence that there is a direct interaction between anti-TSH receptor antibodies and autologous TSH receptors. Divalency of Graves' IgG or linkage of Fab fragments by anti-Fab antiserum proved to be necessary to produce this specific change in the kinetic behaviour of TSH binding sites. Graves' IgG monovalent Fab and Fc fragments had no effect. We suggest that the mechanism by which anti-TSH receptor antibodies in Graves' disease mimick the biological action of TSH is the IgG-induced cross-linkage of TSH receptors.

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