scholarly journals The effect of pH on the characteristics of the binding of nicotinamide–adenine dinucleotide by nicotinamide–adenine dinucleotide specific isocitrate dehydrogenase from pea mitochondria

1970 ◽  
Vol 116 (5) ◽  
pp. 819-824 ◽  
Author(s):  
G. F. Cox ◽  
D. D. Davies
Keyword(s):  
Isocitrate Dehydrogenase ◽  
Nicotinamide Adenine Dinucleotide ◽  
Maximum Velocity ◽  
Nicotinamide Adenine ◽  
Half Maximum ◽  
Ph Optimum ◽  
Effect Of Ph ◽  
Ph Values ◽  
Metabolic Significance

1. The effect of pH on the Vmax. and concentration of NAD+ at half-maximum velocity at a constant isocitrate concentration was examined, and the results were related to the requirements for binding of H+ ions to the enzyme. 2. The effect of varying the NAD+ concentration on the pH optimum with constant isocitrate concentration was studied. 3. A comparison has been made between the effect of isocitrate concentration on the characteristics of binding of NAD+ and the effect of NAD+ concentration on the characteristics of isocitrate binding at three different pH values. 4. The mechanistic and metabolic significance of these studies is considered.

scholarly journals The effects of pH and citrate on the activity of nicotinamide–adenine dinucleotide-specific isocitrate dehydrogenase from pea mitochondria

1969 ◽  
Vol 113 (5) ◽  
pp. 813-820 ◽  
Author(s):  
G. F. Cox ◽  
D. D. Davies
Keyword(s):  
Density Gradient ◽  
Isocitrate Dehydrogenase ◽  
Nicotinamide Adenine Dinucleotide ◽  
Substrate Concentration ◽  
Density Gradient Centrifugation ◽  
Gradient Centrifugation ◽  
Nicotinamide Adenine ◽  
Ph Optimum ◽  
Effects Of Ph ◽  
Metabolic Significance

1. The effect of pH on the co-operative activation of the NAD-specific isocitrate dehydrogenase from pea mitochondria by isocitrate is shown. 2. The interlinked effects of pH on the affinity of the NAD-specific isocitrate dehydrogenase for isocitrate and the dependence of the pH optimum on the substrate concentration are presented. 3. A consideration of the conditions of pH and substrate concentration under which citrate activates the NAD-specific isocitrate dehydrogenase demonstrates similarities between the binding of isocitrate and citrate. 4. A comparison of the effects of citrate and pH on the gross structure of the enzyme is investigated by density-gradient centrifugation. 5. The kinetic interpretations of these results are briefly considered. 6. The metabolic significance of these studies is discussed.

scholarly journals The isocitrate dehydrogenases of Acinetobacter lwoffi. Studies on the regulation of nicotinamide–adenine dinucleotide phosphate-linked isoenzyme

1973 ◽  
Vol 132 (2) ◽  
pp. 215-221 ◽  
Author(s):  
Colin H. Self ◽  
Malcolm G. Parker ◽  
P. David J. Weitzman
Keyword(s):  
Molecular Weight ◽  
Nicotinamide Adenine Dinucleotide ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Nicotinamide Adenine ◽  
Ph Optimum ◽  
Low Concentrations ◽  
Molecular Weight Form ◽  
Metabolic Significance ◽  
Regulatory Sites ◽  
Stimulation Of

Of the two NADP-linked isocitrate dehydrogenases in Acinetobacter lwoffi the higher-molecular-weight form, isoenzyme-II, is reversibly stimulated sixfold by low concentrations of glyoxylate or pyruvate. Kinetic results indicate that this stimulation of activity involves both an increase in Vmax. and a decrease in the apparent Km values for substrates, most markedly that for NADP+. Other changes brought about by glyoxylate or pyruvate include a shift in the pH optimum for activity and an increased stability to inactivation by heat or urea. Mixtures of glyoxylate plus oxaloacetate, known to inhibit isocitrate dehydrogenases from other organisms, produce inhibition of both A. lowffi isoenzymes, and do not reflect the stimulatory specificity of glyoxylate for isoenzyme-II. Isoenzyme-II is also stimulated by AMP and ADP, but the activation by glyoxylate or pyruvate is shown to be quite independent of the adenylate activation. Differential desensitization of the enzyme by urea to the two types of activator further supports the view that the enzyme possesses two distinct allosteric regulatory sites. The metabolic significance of the activations is discussed.

scholarly journals Effect of pH on the inhibition of the nicotinamide–adenine dinucleotide-specific isocitrate dehydrogenase from baker's yeast by anions

1968 ◽  
Vol 109 (3) ◽  
pp. 361-368 ◽  
Author(s):  
C. Cennamo ◽  
G. Montecuccoli ◽  
G. Bonaretti ◽  
L. Razzoli
Keyword(s):  
Isocitrate Dehydrogenase ◽  
Nicotinamide Adenine Dinucleotide ◽  
Substrate Concentration ◽  
Ph Dependence ◽  
Chloride Concentration ◽  
Enzymic Activity ◽  
Baker’S Yeast ◽  
Nicotinamide Adenine ◽  
Baker's Yeast ◽  
Effect Of Ph

1. The sensitivity of the NAD+-specific isocitrate dehydrogenase from baker's yeast towards inhibition by anions decreases with decrease in pH. The patterns of the pH-dependence of the enzymic activity can be explained by this effect. 2. In the presence of a high isocitrate concentration, citrate, unlike AMP, has no antagonizing effect on the inhibition of the enzyme by anions. In the presence of AMP, citrate inhibits the enzyme at high isocitrate concentration and activates at low isocitrate concentration. 3. The effects on the enzymic activity of the previous incubation of the enzyme were studied in relation to the substrate concentration, the chloride concentration and the presence of citrate and AMP.

scholarly journals Glycolate kinase activity in human red cells

Blood ◽  
1985 ◽  
Vol 65 (2) ◽  
pp. 480-483 ◽  
Author(s):  
S Fujii ◽  
E Beutler
Keyword(s):  
Pyruvate Kinase ◽  
Adenosine Triphosphate ◽  
Kinase Activity ◽  
Maximum Velocity ◽  
Red Cells ◽  
Half Maximum ◽  
Ph Optimum ◽  
Pyruvate Kinase Deficiency ◽  
Low Activity ◽  
Human Red Cells

Abstract Human red cells manifest glycolate kinase activity. This activity copurifies with pyruvate kinase and is decreased in the red cells of subjects with hereditary pyruvate kinase deficiency. Glycolate kinase activity was detected in the presence of FDP or glucose-1,6-P2. In the presence of 1 mmol/L FDP, the Km for adenosine triphosphate (ATP) was 0.28 mmol/L and a half maximum velocity for glycolate was obtained at 40 mmol/L. The pH optimum of the reaction was over 10.5 With 10 mumol/L FDP, 500 mumol/L glucose-1,6-P2, 2 mmol/L ATP, 5 mmol/L MgCl2, and 50 mmol/L glycolate at pH 7.5, glycolate kinase activity was calculated to be approximately 0.0013 U/mL RBC. In view of this low activity even in the presence of massive amounts of glycolate, the glycolate kinase reaction cannot account for the maintenance of the reported phosphoglycolate level in human red cells.

scholarly journals Glycolate kinase activity in human red cells

Blood ◽  
1985 ◽  
Vol 65 (2) ◽  
pp. 480-483
Author(s):  
S Fujii ◽  
E Beutler
Keyword(s):  
Pyruvate Kinase ◽  
Adenosine Triphosphate ◽  
Kinase Activity ◽  
Maximum Velocity ◽  
Red Cells ◽  
Half Maximum ◽  
Ph Optimum ◽  
Pyruvate Kinase Deficiency ◽  
Low Activity ◽  
Human Red Cells

Human red cells manifest glycolate kinase activity. This activity copurifies with pyruvate kinase and is decreased in the red cells of subjects with hereditary pyruvate kinase deficiency. Glycolate kinase activity was detected in the presence of FDP or glucose-1,6-P2. In the presence of 1 mmol/L FDP, the Km for adenosine triphosphate (ATP) was 0.28 mmol/L and a half maximum velocity for glycolate was obtained at 40 mmol/L. The pH optimum of the reaction was over 10.5 With 10 mumol/L FDP, 500 mumol/L glucose-1,6-P2, 2 mmol/L ATP, 5 mmol/L MgCl2, and 50 mmol/L glycolate at pH 7.5, glycolate kinase activity was calculated to be approximately 0.0013 U/mL RBC. In view of this low activity even in the presence of massive amounts of glycolate, the glycolate kinase reaction cannot account for the maintenance of the reported phosphoglycolate level in human red cells.

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