Thiamine Triphosphate Synthesis in Rat Brain Occurs in Mitochondria
and Is Coupled to the Respiratory Chain |
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Authors: | Marjorie Gangolf Pierre Wins Marc Thiry Bena?ssa El Moualij Lucien Bettendorff |
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Institution: | From ‡GIGA-Neurosciences (B36) and ;the §Department of Human Histology, University of Liège, Avenue de l''Hôpital 1, B-4000 Liège 1 (Sart Tilman), Belgium B-4000 Liège, Belgium |
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Abstract: | In animals, thiamine deficiency leads to specific brain lesions, generally
attributed to decreased levels of thiamine diphosphate, an essential cofactor in
brain energy metabolism. However, another far less abundant derivative, thiamine
triphosphate (ThTP), may also have a neuronal function. Here, we show that in
the rat brain, ThTP is essentially present and synthesized in mitochondria. In
mitochondrial preparations from brain (but not liver), ThTP can be produced from
thiamine diphosphate and Pi. This endergonic process is coupled to
the oxidation of succinate or NADH through the respiratory chain but cannot be
energized by ATP hydrolysis. ThTP synthesis is strongly inhibited by respiratory
chain inhibitors, such as myxothiazol and inhibitors of the
H+ channel of F0F1-ATPase. It is
also impaired by disruption of the mitochondria or by depolarization of the
inner membrane (by protonophores or valinomycin), indicating that a
proton-motive force (Δp) is required. Collapsing
Δp after ThTP synthesis causes its rapid
disappearance, suggesting that both synthesis and hydrolysis are catalyzed by a
reversible H+-translocating ThTP synthase. The synthesized
ThTP can be released from mitochondria in the presence of external
Pi. However, ThTP probably does not accumulate in the cytoplasm
in vivo, because it is not detected in the cytosolic
fraction obtained from a brain homogenate. Our results show for the first time
that a high energy triphosphate compound other than ATP can be produced by a
chemiosmotic type of mechanism. This might shed a new light on our understanding
of the mechanisms of thiamine deficiency-induced brain lesions. |
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Keywords: | Alcohol Immunophilin Mass Spectrometry (MS) Receptor regulation Ubiquitination Brain Chemiosmotic Mechanism Thiamine Triphosphate |
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