Open AccessRegulation of Pyruvate‐Dehydrogenase Interconversion in Rat‐Liver Mitochondria as Related to the Phosphorylation State of Intramitochondrial Adenine Nucleotides
Author(s) -
Wieland Otto H.,
Portenhauser Rudolf
Publication year - 1974
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1974.tb03584.x
Subject(s) - uncoupling agents , pyruvate dehydrogenase complex , pyruvate dehydrogenase kinase , biochemistry , adenine nucleotide , atp–adp translocase , hexokinase , mitochondrion , oxidative phosphorylation , adenosine triphosphate , chemiosmosis , pyruvate decarboxylation , pyruvate dehydrogenase phosphatase , oligomycin , glycolysis , submitochondrial particle , dehydrogenase , adenosine diphosphate , substrate level phosphorylation , atp synthase , phosphorylation , biology , nucleotide , enzyme , inner mitochondrial membrane , atpase , platelet , platelet aggregation , gene , immunology
The proportions of active (dephospho) and inactive (phospho) forms of pyruvate dehydrogenase, and the corresponding adenine nucleotide contents have been determined in isolated rat liver mitochondria. Uncoupling of oxidative phosphorylation by carbonylcyanide m ‐chlorophenylhyclrazone leads, in a dose‐dependent manner, to conversion of pyruvate dehydrogenase from the inactive to the active form. The effect of uncoupler on enzyme interconversion is counteracted by 2‐oxoglutarate which also increases the low ATP/ADP ratios resulting from uncoupling. Similar effects as with carbonylcyanide m ‐chlorophenylhydrazone are obtained with Ca 2+ and rotenone. In the latter case 2‐oxoglutarate again restores both the equilibrium of the active and inactive forms of pyruvate dehydrogenase and the mitochondrial ATP/ADP ratio. The elevation of the ATP potential by 2‐oxoglutarate is most likely due to substrate level phosphorylation. Different ATP/ADP ratios were established in mitochondria by adding glucose and varying amounts of hexokinase. On plotting the ratios of ATP/ADP against phosphoenzyme/dephosphoenzyme ratios a straight correlation was obtained. From this it can be derived that a drop of ATP/ADP from 1 to values below 0.4 is accompanied by an about eight‐fold increase in pyruvate dehydrogenase activity, due to conversion of the phosphoenzyme to the dephospho form. The inactivating effect of a high ATP potential on pyruvate dehydrogenase is missing in the presence of pgruvate as single substrate. It is suggested that, in vivo , an increased (or decreased) supply of free fatty acids leads to an elevation (or lowering) of the mitochondrial ATP potential whereby adenine nucleotide translocase inhibition by long‐chain acyl‐CoA may be involved. These fluctuations of the mitochondrial energy state may represent a basic mechanism for the regulation of the pyruvate dehydrogenase system.