scholarly journals Comparative development of the pyruvate dehydrogenase complex and citrate synthase in rat brain mitochondria

1986 ◽  
Vol 238 (3) ◽  
pp. 729-736 ◽  
Author(s):  
G D A Malloch ◽  
L A Munday ◽  
M S Olson ◽  
J B Clark
Keyword(s):  
Enzyme Activity ◽  
Rat Brain ◽  
Pyruvate Dehydrogenase ◽  
Citrate Synthase ◽  
Post Partum ◽  
Pyruvate Dehydrogenase Complex ◽  
Brain Mitochondria ◽  
Rat Brain Mitochondria ◽  
Developing Rat ◽  
Dehydrogenase Complex

The enzyme activity of the pyruvate dehydrogenase complex (PDHC) was measured in mitochondria prepared from developing rat brain, before and after steady-state dephosphorylation of the E1 alpha subunit. A marked increase in dephosphorylated (fully activated) PDHC activity occurred between days 10 and 15 post partum, which represented approx. 60% of the difference in fully activated PDHC activity measured in foetal and adult rat brain mitochondria. There was no detectable change in the active proportion of the enzyme during mitochondrial preparation nor any qualitative alteration in the detectable catalytic and regulatory components of the complex, which might account for developmental changes in PDHC activity. The PDHC protein content of developing rat brain mitochondria and homogenates was measured by an enzyme-linked immunoadsorbent assay. The development of PDHC protein in both fractions agreed closely with the development of the PDHC activity. The results suggest that the developmental increase in PDHC activity is due to increased synthesis of PDHC protein, which is partly a consequence of an increase in mitochondrial numbers. However, the marked increase in PDHC activity measured between days 10 and 15 post partum is mainly due to an increase in the amount of PDHC per mitochondrion. The development of citrate synthase enzyme activity and protein was measured in rat brain homogenates and mitochondria. As only a small increase in citrate synthase activity and protein was detected in mitochondria between days 10 and 15 post partum, the marked increase in PDHC protein and enzyme activity may represent specific PDHC synthesis. As several indicators of acquired neurological competence become apparent during this period, it is proposed that preferential synthesis of PDHC may be crucial to this process. The results are discussed with respect to the possible roles played by PDHC in changes of respiratory-substrate utilization and the acquisition of neurological competence occurring during the development of the brain of a non-precocial species such as the rat.

scholarly journals Effect of phenylpyruvate on pyruvate dehydrogenase activity in rat brain mitochondria

1973 ◽  
Vol 134 (2) ◽  
pp. 539-544 ◽  
Author(s):  
John M. Land ◽  
John B. Clark
Keyword(s):  
Rat Brain ◽  
Dehydrogenase Activity ◽  
Pyruvate Dehydrogenase ◽  
Pyruvate Dehydrogenase Complex ◽  
Competitive Inhibitor ◽  
Brain Mitochondria ◽  
Significant Inhibition ◽  
Complex Activity ◽  
Rat Brain Mitochondria ◽  
Dehydrogenase Complex

1. The effects of phenylpyruvate, a metabolite produced in phenylketonuria, on the pyruvate dehydrogenase-complex activity were investigated in rat brain mitochondria. 2. Pyruvate dehydrogenase activity was measured by two methods, one measuring the release of 14CO2 from [1-14C]pyruvate and the other measuring the acetyl-CoA formed by means of the coupling enzyme, pigeon liver arylamine acetyltransferase (EC 2.3.1.5). In neither case was there significant inhibition of the pyruvate dehydrogenase complex by phenylpyruvate at concentrations below 2mm. 3. However, phenylpyruvate acted as a classical competitive inhibitor of the coupling enzyme arylamine acetyltransferase, with a Ki of 100μm. 4. It was concluded that the inhibition of pyruvate dehydrogenase by phenylpyruvate is unlikely to be a primary enzyme defect in phenylketonuria.

scholarly journals Development of mitochondrial energy metabolism in rat brain

1977 ◽  
Vol 164 (2) ◽  
pp. 339-348 ◽  
Author(s):  
John M. Land ◽  
Robert F. G. Booth ◽  
Ruud Berger ◽  
John B. Clark
Keyword(s):  
Rat Brain ◽  
Pyruvate Dehydrogenase ◽  
Citrate Synthase ◽  
Aerobic Glycolysis ◽  
Biological Significance ◽  
Brain Mitochondria ◽  
Developmental Pattern ◽  
Mitochondrial Energy Metabolism ◽  
Rat Brain Mitochondria ◽  
Total Brain

1. The development of pyruvate dehydrogenase and citrate synthase activity in rat brain mitochondria was studied. Whereas the citrate synthase activity starts to increase at about 8 days after birth, that of pyruvate dehydrogenase starts to increase at about 15 days. Measurements of the active proportion of pyruvate dehydrogenase during development were also made. 2. The ability of rat brain mitochondria to oxidize pyruvate follows a similar developmental pattern to that of the pyruvate dehydrogenase. However, the ability to oxidize 3-hydroxybutyrate shows a different developmental pattern (maximal at 20 days and declining by half in the adult), which is compatible with the developmental pattern of the ketone-body-utilizing enzymes. 3. The developmental pattern of both the soluble and the mitochondrially bound hexokinase of rat brain was studied. The total brain hexokinase activity increases markedly at about 15 days, which is mainly due to an increase in activity of the mitochondrially bound form, and reaches the adult situation (approx. 70% being mitochondrial) at about 30 days after birth. 4. The release of the mitochondrially bound hexokinase under different conditions by glucose 6-phosphate was studied. There was insignificant release of the bound hexokinase in media containing high KCl concentrations by glucose 6-phosphate, but in sucrose media half-maximal release of hexokinase was achieved by 70μm-glucose 6-phosphate 5. The production of glucose 6-phosphate by brain mitochondria in the presence of Mg2++glucose was demonstrated, together with the inhibition of this by atractyloside. 6. The results are discussed with respect to the possible biological significance of the similar developmental patterns of pyruvate dehydrogenase and the mitochondrially bound kinases, particularly hexokinase, in the brain. It is suggested that this association may be a mechanism for maintaining an efficient and active aerobic glycolysis which is necessary for full neural expression.

scholarly journals Proportion of active dephosphorylated pyruvate dehydrogenase complex in heart and isolated heart mitochondria is decreased in obese hyperinsulinaemic mice

1984 ◽  
Vol 217 (1) ◽  
pp. 117-121 ◽  
Author(s):  
A L Kerbey ◽  
I D Caterson ◽  
P F Williams ◽  
J R Turtle
Keyword(s):  
Insulin Resistance ◽  
Enzyme Activity ◽  
Pyruvate Dehydrogenase ◽  
Glucose Oxidation ◽  
Isolated Heart ◽  
Pyruvate Dehydrogenase Complex ◽  
Heart Mitochondria ◽  
Mouse Heart ◽  
Inhibitory Effects ◽  
Dehydrogenase Complex

The proportion of active, dephosphorylated, pyruvate dehydrogenase complex was decreased in the mouse heart by obesity (by 56%), and this decrease in enzyme activity persisted during preparation and extraction of heart mitochondria. Phosphorylation and inactivation of pyruvate dehydrogenase may be a major factor in mediating the inhibitory effects of obesity on glucose oxidation in muscle, and this may represent an important mechanism in the development and/or expression of cellular insulin-resistance.

Pyruvate Dehydrogenase Activity in Osmotically Shocked Rat Brain Mitochondria: Stimulation by Oxaloacetate

1988 ◽  
Vol 50 (3) ◽  
pp. 673-680 ◽  
Author(s):  
Richard H. Haas ◽  
Geoffrey Thompson ◽  
Bernard Morris ◽  
Kelly Conright ◽  
Torre Andrews
Keyword(s):  
Rat Brain ◽  
Dehydrogenase Activity ◽  
Pyruvate Dehydrogenase ◽  
Brain Mitochondria ◽  
Rat Brain Mitochondria

scholarly journals The regulation and glutamate metabolism by tricarboxylic acid-cycle activity in rat brain mitochondria

1978 ◽  
Vol 172 (1) ◽  
pp. 155-162 ◽  
Author(s):  
Steven C. Dennis ◽  
John B. Clark
Keyword(s):  
Rat Brain ◽  
Citrate Synthase ◽  
Tricarboxylic Acid Cycle ◽  
Brain Mitochondria ◽  
Inhibitory Effect ◽  
Tricarboxylic Acid ◽  
Acid Cycle ◽  
Rat Brain Mitochondria ◽  
Fixed Concentration ◽  
K Concentration

1. The interrelationship of metabolism of pyruvate or 3-hydroxybutyrate and glutamate transamination in rat brain mitochondria was studied. 2. If brain mitochondria are incubated in the presence of equimolar concentrations of pyruvate and glutamate and the K+ concentration is increased from 1 to 20mm, the rate of pyruvate utilization is increased 3-fold, but the rate of production of aspartate and 2-oxoglutarate is decreased by half. 3. Brain mitochondria incubated in the presence of a fixed concentration of glutamate (0.87 or 8.7mm) but different concentrations of pyruvate (0 to 1mm) produce aspartate at rates that decrease as the pyruvate concentration is increased. At 1mm-pyruvate, the rate of aspartate production is decreased to 40% of that when zero pyruvate was present. 4. Brain mitochondria incubated in the presence of glutamate and malate alone produce 2-oxoglutarate at rates stoicheiometric with the rate of aspartate production. Both the 2-oxoglutarate and aspartate accumulate extramitochondrially. 5. Externally added 2-oxoglutarate has little inhibitory effect (Ki approx. 31mm) on the production of aspartate from glutamate by rat brain mitochondria. 6. It is concluded that the inhibitory effect of increased C2 flux into the tricarboxylic acid cycle on glutamate transamination is caused by competition for oxaloacetate between the transaminase and citrate synthase. 7. Evidence is provided from a reconstituted malate–aspartate (or Borst) cycle with brain mitochondria that increased C2 flux into the tricarboxylic acid cycle from pyruvate may inhibit the reoxidation of exogenous NADH. These results are discussed in the light of the relationship between glycolysis and reoxidation of cytosolic NADH by the Borst cycle and the requirement of the brain for a continuous supply of energy.

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