scholarly journals The kinetics and reaction mechanism of the nicotinamide–adenine dinucleotide phosphate-specific glycerol dehydrogenase of rat skeletal muscle

1967 ◽  
Vol 105 (3) ◽  
pp. 1067-1073 ◽  
Author(s):  
C. J. Toews
Keyword(s):  
Skeletal Muscle ◽  
Reaction Mechanism ◽  
Nicotinamide Adenine Dinucleotide ◽  
Initial Velocity ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Product Inhibition ◽  
Glycerol Dehydrogenase ◽  
Velocity Analysis ◽  
Rat Skeletal Muscle ◽  
Ammonium Sulphate Fractionation

The NADP-specific glycerol dehydrogenase of rat skeletal muscle has been partially purified by ammonium sulphate fractionation. The enzyme has been studied kinetically by initial-velocity analysis, product inhibition and inhibition by fluoride. The experimental results indicate that the reaction mechanism for the enzyme is ordered such that the first product leaves the enzyme before the addition of the second substrate.

scholarly journals Kinetic studies with skeletal-muscle hexokinase

1966 ◽  
Vol 100 (3) ◽  
pp. 739-744 ◽  
Author(s):  
CJ Toews
Keyword(s):  
Skeletal Muscle ◽  
Initial Velocity ◽  
Gel Filtration ◽  
Kinetic Studies ◽  
Competitive Inhibitor ◽  
Product Inhibition ◽  
Velocity Analysis ◽  
Sequential Mechanism ◽  
Ammonium Sulphate Fractionation ◽  
Ordered Sequential Mechanism

Rat skeletal-muscle hexokinase was partially purified by ammonium sulphate fractionation and gel filtration. The mechanism of the skeletal-muscle hexokinase was studied kinetically by initial-velocity analysis and product inhibition. Glucose 6-phosphate was a non-competitive inhibitor of glucose and ATP. ADP was a non-competitive inhibitor of glucose and a competitive inhibitor of ATP. The data on product inhibition and initial-velocity analysis of skeletal-muscle hexokinase support an ordered sequential mechanism (ordered Bi Bi) where the addition of substrates and release of products is in the order: ATP, glucose, glucose 6-phosphate and ADP.

Oxidative decarboxylation of isocitric acid in the presence of montmorillonite

Clay Minerals ◽  
1990 ◽  
Vol 25 (1) ◽  
pp. 27-37 ◽  
Author(s):  
A. Naidja ◽  
B. Siffert
Keyword(s):  
Catalytic Activity ◽  
Reaction Mechanism ◽  
Nicotinamide Adenine Dinucleotide ◽  
Reaction Rate ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Oxidative Decarboxylation ◽  
Enzymatic System ◽  
Exchangeable Cation ◽  
Isocitric Acid ◽  
Dehydrogenase Enzyme

AbstractIsocitric acid oxidative decarboxylation was realized in the absence and in the presence of homoionic Na+-, Mn2+-, and Cu2+-montmorillonite. The catalytic activity of the clay depends upon the nature of the interlayer exchangeable cation. Isocitric acid is transformed into α-ketoglutaric acid under the action of the clay mineral saturated with Na+ cations which do not form a complex with the isocitrate anion. Nevertheless, the reaction rate is very much lower than in the presence of the enzymatic system (isocitrate dehydrogenase enzyme and nicotinamide adenine dinucleotide phosphate coenzyme). The reaction mechanism in the presence of clay is given showing the different steps of the transformation.

INTRACELLULAR DISTRIBUTION AND SOME PROPERTIES OF HEXOKINASE OF BOVINE ADRENAL MEDULLA

1966 ◽  
Vol 44 (6) ◽  
pp. 879-891 ◽  
Author(s):  
C. J. Toews
Keyword(s):  
Adenosine Triphosphate ◽  
Adrenal Medulla ◽  
Initial Velocity ◽  
Adenosine Diphosphate ◽  
Product Inhibition ◽  
Intracellular Distribution ◽  
Velocity Analysis ◽  
Bovine Adrenal Medulla ◽  
Sequential Mechanism ◽  
Ordered Sequential Mechanism

The intracellular distribution of the hexokinase of the adrenal medulla was studied. Most of the hexokinase was found, in about equal amounts, in the mitochondria and the nonparticulate cytoplasm. The amount of hexokinase associated with the mitochondria was shown to be dependent on the hexokinase concentration in the medium surrounding the mitochondria.The hexokinase of the adrenal medulla was shown to be noncompetitively inhibited by adenosine diphosphate (ADP) with respect to glucose and adenosine triphosphate (ATP). It was competitively inhibited with respect to glucose by mannose, fructose, and galactose. Glucose-6-phosphate (0.09 M) did not inhibit the hexokinase. The data on product inhibition and initial velocity analysis support the concept of an ordered sequential mechanism for adrenal-medulla hexokinase.

scholarly journals Kynurenine Pathway of Tryptophan Metabolism: Regulatory and Functional Aspects

2017 ◽  
Vol 10 ◽  
pp. 117864691769193 ◽  
Author(s):  
Abdulla A-B Badawy
Keyword(s):  
Nicotinamide Adenine Dinucleotide ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Active Role ◽  
Kynurenine Pathway ◽  
Product Inhibition ◽  
Nicotinamide Adenine ◽  
Functional Aspects ◽  
Glucocorticoid Induction ◽  
Ifn Γ ◽  
Reduced Nicotinamide Adenine Dinucleotide

Regulatory and functional aspects of the kynurenine (K) pathway (KP) of tryptophan (Trp) degradation are reviewed. The KP accounts for ~95% of dietary Trp degradation, of which 90% is attributed to the hepatic KP. During immune activation, the minor extrahepatic KP plays a more active role. The KP is rate-limited by its first enzyme, Trp 2,3-dioxygenase (TDO), in liver and indoleamine 2,3-dioxygenase (IDO) elsewhere. TDO is regulated by glucocorticoid induction, substrate activation and stabilization by Trp, cofactor activation by heme, and end-product inhibition by reduced nicotinamide adenine dinucleotide (phosphate). IDO is regulated by IFN-γ and other cytokines and by nitric oxide. The KP disposes of excess Trp, controls hepatic heme synthesis and Trp availability for cerebral serotonin synthesis, and produces immunoregulatory and neuroactive metabolites, the B3 “vitamin” nicotinic acid, and oxidized nicotinamide adenine dinucleotide. Various KP enzymes are undermined in disease and are targeted for therapy of conditions ranging from immunological, neurological, and neurodegenerative conditions to cancer.

scholarly journals Purification and comparative properties of isoenzymes of nicotinamide–adenine dinucleotide phosphate–isocitrate dehydrogenase from rat heart and liver

1972 ◽  
Vol 129 (5) ◽  
pp. 1003-1011 ◽  
Author(s):  
M. Islam ◽  
Joyce L. Bell ◽  
D. N. Baron
Keyword(s):  
Myocardial Infarction ◽  
Ion Exchange ◽  
Ammonium Sulphate ◽  
Isocitrate Dehydrogenase ◽  
Nicotinamide Adenine Dinucleotide ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Differential Sensitivity ◽  
Michaelis Constants ◽  
Ammonium Sulphate Fractionation ◽  
Cytoplasmic Location

1. Rat liver and heart major isoenzymes of NADP–isocitrate dehydrogenase have each been purified about 100-fold by a combination of ammonium sulphate fractionation and chromatography on ion-exchange cellulose and their properties compared. 2. The properties were similar in respect of pH, inhibition by Hg2+and Michaelis constants for isocitrate and NADP. 3. Some of the properties of the isoenzymes were different. 4. The heart isoenzyme was activated about 210% by 0.8m-ammonium sulphate whereas the liver isoenzyme was unaffected. The heart isoenzyme showed greater sensitivity to inactivation by heat (30°C for 30min), whereas the liver isoenzyme was more sensitive to inactivation by p-chloromercuribenzoate and by Cu2+. 5. The Michaelis constants with 3-acetylpyridine–adenine dinucleotide phosphate showed a twofold difference between liver and heart isoenzyme. 6. The differential sensitivity to heat and its mainly non-cytoplasmic location may be an explanation of the failure of plasma isocitrate dehydrogenase activity to increase after a myocardial infarction.

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