title: Thiamine triphosphate synthesis in rat brain occurs in mitochondria and is coupled to the respiratory chain.
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 P(i). 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 F(0)F(1)-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 (Deltap) is required. Collapsing Deltap 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 P(i). 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.
authors.affiliation: GIGA-Neurosciences (B36), University of Liège, Avenue de l'Hôpital 1, B-4000 Liège 1 (Sart Tilman), Belgium B-4000 Liège, Belgium.
authors.forename: Marjorie
authors.initials: M
authors.lastname: Gangolf
authors.forename: Pierre
authors.initials: P
authors.lastname: Wins
authors.forename: Marc
authors.initials: M
authors.lastname: Thiry
authors.forename: Benaïssa
authors.initials: B
authors.lastname: El Moualij
authors.forename: Lucien
authors.initials: L
authors.lastname: Bettendorff
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D004579:Electron Transport / Q000187:drug effects; D006868:Hydrolysis / Q000187:drug effects; D007700:Kinetics; D008297:Male; D008689:Methacrylates / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D009840:Oligomycins / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism; D018892:Proton-Motive Force / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D013194:Staining and Labeling; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D013379:Substrate Specificity / Q000187:drug effects; D013696:Temperature; D013838:Thiamine Triphosphate / Q000096:biosynthesis*; D013844:Thiazoles / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D008689:Methacrylates; D009840:Oligomycins; D010710:Phosphates; D013844:Thiazoles; D014634:Valinomycin; D013838:Thiamine Triphosphate; D004024:Dicyclohexylcarbodiimide; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; C030517:myxothiazol; D000255:Adenosine Triphosphate