Pyruvate dehydrogenase kinase

About: Pyruvate dehydrogenase kinase is a research topic. Over the lifetime, 4224 publications have been published within this topic receiving 161052 citations. The topic is also known as: [pyruvate dehydrogenase (lipoamide)] kinase & pyruvate dehydrogenase (lipoamide) kinase.

The pathway of formation of acetate and succinate from pyruvate by Bacteroides succinogenes.

Abstract: Bacteroides succinogenes produces acetate and succinate as major products of carbohydrate fermentation. An investigation of the enzymes involved indicated that pyruvate is oxidized by a flavin-dependent pyruvate cleavage enzyme to acetyl-CoA and CO2. Active CO2 exchange is associated with the pyruvate oxidation system. Reduction of flavin nucleotides is CoASH-dependent and does not require ferredoxin. Acetyl-CoA is further metabolized via acetyl phosphate to acetate and ATP. Reduced flavin nucleotide is used to reduce fumarate to succinate by a particulate flavin-specific fumarate reductase reaction which may involve cytochrome b. Phosphoenolpyruvate (PEP) is carboxylated to oxalacetate by a GDP- specific PEP carboxykinase. Oxalacetate, in turn, is converted to malate by a pyridine nucleotide-dependent malate dehydrogenase. The organism has a NAD-dependent glyceraldehyde-3-phosphate dehydrogenase. The data suggest that reduced pyridine nucleotides generated during glycolysis are oxidized in malate formation and that the electrons generated during pyruvate oxidation are used to reduce fumarate to succinate.

Decreased Expression of Cytosolic Pyruvate Kinase in Potato Tubers Leads to a Decline in Pyruvate Resulting in an in Vivo Repression of the Alternative Oxidase

Abstract: The aim of this work was to investigate the effect of decreased cytosolic pyruvate kinase (PKc) on potato (Solanum tuberosum) tuber metabolism. Transgenic potato plants with strongly reduced levels of PKc were generated by RNA interference gene silencing under the control of a tuber-specific promoter. Metabolite profiling showed that decreased PKc activity led to a decrease in the levels of pyruvate and some other organic acids involved in the tricarboxylic acid cycle. Flux analysis showed that this was accompanied by changes in carbon partitioning, with carbon flux being diverted from glycolysis toward starch synthesis. However, this metabolic shift was relatively small and hence did not result in enhanced starch levels in the tubers. Although total respiration rates and the ATP to ADP ratio were largely unchanged, transgenic tubers showed a strong decrease in the levels of alternative oxidase (AOX) protein and a corresponding decrease in the capacity of the alternative pathway of respiration. External feeding of pyruvate to tuber tissue or isolated mitochondria resulted in activation of the AOX pathway, both in the wild type and the PKc transgenic lines, providing direct evidence for the regulation of AOX by changes in pyruvate levels. Overall, these results provide evidence for a crucial role of PKc in the regulation of pyruvate levels as well as the level of the AOX in heterotrophic plant tissue, and furthermore reveal that these parameters are interlinked in vivo.

Regulation of rat liver L-type pyruvate kinase mRNA by insulin and by fructose.

Abstract: The effects have been studied of streptozotocin-induced diabetes and subsequent insulin administration or feeding of a high fructose diet on the amount of enzyme protein and mRNA activity of L-type pyruvate kinase in rat liver. Diabetes markedly decreased the L-type enzyme activity in rat liver and insulin treatment resulted in restoration of the enzyme activity to normal. A high fructose diet also increased the enzyme activity in diabetic rats but to a lesser extent. Immunochemical analysis showed that these alterations in the enzyme activity were due to changes in the amount of immunoreactive enzyme protein. The mechanism of the changes was studied further by assaying the level of functional mRNA coding for this enzyme in a nuclease-treated reticulocyte lysate system with total RNA isolated from rat liver. L-type pyruvate kinase mRNA, expressed as a percentage of the total protein synthesized, was greatly decreased in diabetic rats. Insulin administration resulted in recovery of the mRNA activity to the normal level within 24 h. The lag period before accumulation of translatable mRNA of the L-type enzyme was about 4-5 h. The mRNA activity was also increased in diabetic rats fed a high fructose diet. This fructose effect, which was much smaller than the insulin effect, was maximal after feeding fructose diet for one day. These changes were approximately comparable to the changes in enzyme activity. Thus, it is suggested that regulations of rat liver L-type pyruvate kinase by insulin and by fructose are primarily due to changes in the level of translatable mRNA of this enzyme.

Interconversion of Pyruvate Dehydrogenase in the Isolated Perfused Rat Liver

Abstract: Active form and total activity of pyruvate dehydrogenase were measured in homogenates prepared from tissue samples obtained from the isolated rat liver during perfusion. In the absence of substrate, the active portion accounted for about 20% of total activity in livers from fed rats, whereas only about 10% were found to be active in livers from starved rats. These activities remained rather constant during a perfusion period of 120 min. Addition of 10 mM pyruvate to the perfusion medium resulted in an immediate, three-fold increase of the active pyruvate dehydrogenase. A similar effect was exerted by 20 mM fructose, which is known to be rapidly converted to pyruvate in liver. 10 mM lactate led to a considerably smaller increase of pyruvate dehydrogenase activity as compared to the effects obtained with pyruvate or fructose. Total activities of the enzyme did not change significantly during perfusion. If the activities of active pyruvate dehydrogenase from livers perfused with and without substrate were plotted against medium pyruvate concentrations an exponential correlation could be observed. Addition of 2 mM oleate abolished the effects of fructose or pyruvate on the formation of active pyruvate dehydrogenase. The simultaneous addition of d-(+)-decanoylcarnitine inhibited the action of oleate, indicating that fatty acid oxidation is required for the inactivation of pyruvate dehydrogenase by interconversion of the active to the inactive form. The possible physiological significance of pyruvate and fatty acids in the regulation of pyruvate dehydrogenase interconversion is discussed.