Thiamine metabolism - Homo sapiens [human]

Curator(s): Maria Zangara

Thiamin(e), also known as vitamin B1, is known to play a fundamental role in energy metabolism. It consists of a pyrimidine ring (2,5-dimethyl-6-aminopyrimidine) and a thiazolium ring (4-methyl-5-hydroxy ethyl thiazole) joined by a methylene bridge. Thiamine is found in a wide variety of foods at low concentrations. Thiamine is released by the action of phosphatase and pyrophosphatase in the upper small intestine. At low concentrations the process is carrier mediated and at higher concentrations, absorption occurs via passive diffusion. Active transport is greatest in the jejunum and ileum (it is inhibited by alcohol consumption and by folic deficiency). The majority of thiamine in serum is bound to proteins, mainly albumin. Uptake of thiamine by cells of the blood and other tissues occurs via active transport and passive diffusion. About 80% of intracellular thiamine is phosphorylated and most is bound to proteins. Thiamine and its acid metabolites (2-methyl-4-amino-5-pyrimidine carboxylic acid, 4-methyl-thiazole-5-acetic acid and thiamine acetic acid) are excreted principally in the urine. Thiamine is mainly the transport form of the vitamin, while the active forms are phosphorylated thiamine derivatives. There are four known natural thiamine phosphate derivatives: thiamine monophosphate (ThMP), thiamine diphosphate (ThDP), also sometimes called thiamine pyrophosphate (TPP), thiamine triphosphate (ThTP), and the recently discovered adenosine thiamine triphosphate (AThTP) and adenosine thiamine diphosphate (AThDP). Thiamine monophosphate (TMP) is an intermediate to facilitate the synthesis of free thiamine to thiamine diphosphate and triphosphate. The synthesis of thiamine diphosphate (ThDP), also known as thiamine pyrophosphate (TPP) or cocarboxylase, is catalyzed by an enzyme called thiamine diphosphokinase. TPP activates decarboxylation of pyruvate in the pyruvate dehydrogenase complex. This complex is a group of enzymes and cofactors that form acetyl CoA that condenses with oxaloacetate to form citrate, the first component of the citric acid cycle.    
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Thiamine metabolism - Homo sapiens [human] node1 1-[5' -Phosphoribosyl]-5 -aminoimidazole [AIR] ThiC node1->ThiC node2 4-Amino -5-hydroxymethyl -2-methylpyrimidine node3 node2->node3 node4 4-Amino -2-methyl -5-phosphomethylpyrimidine node3->node4 node5 node4->node5 node6 2-Methyl -4-amino -5-hydroxymethylpyrimidine diphosphate node5->node6 node7 node6->node7 Thiamine phosphate node7->Thiamine phosphate node8 Thiamine phosphate->node8 node13 3.1.3.- Thiamine phosphate->node13 Thiamine diphosphate node8->Thiamine diphosphate node9 Thiamine diphosphate->node9 node10 Thiamine diphosphate->node10 node12 Thiamine diphosphate->node12 node9->Thiamine diphosphate Thiamine triphosphate node9->Thiamine triphosphate node11 Thiamine triphosphate->node11 node10->Thiamine triphosphate node11->Thiamine diphosphate node12->Thiamine phosphate Thiamine node13->Thiamine Thiamine->node9 node14 Thiamine->node14 node15 Thiamine->node15 node16 Thiamine->node16 node18 Thiamine->node18 node14->Thiamine phosphate Thiamine acetic acid node15->Thiamine acetic acid Thiamine aldehyde node15->Thiamine aldehyde Thiamine aldehyde->node15 Heteropynthiamine node16->Heteropynthiamine node17 5-(2 -Hydroxyethyl)-4 -methylthiazole node16->node17 node19 node17->node19 Purine metabolism Purine metabolism->node1 node18->node2 node18->node17 node20 4 Methyl -5 -(2-phosphoethyl) -thiazole node19->node20 node20->node7 node21 Glyceraldehyde-3P node21->node17 node22 2 Pyruvate Pyruvate->node17 Pyruvate->node22 Pyruvate node23 L-Cysteine node25 node23->node25 node24 (Thil)-SH node24->node25 node26 (Thil)-SSH node25->node26 Thil node26->Thil node27 (ThiS)-COOH ThiF node27->ThiF node28 (ThiS) -CO -AMP ThiF->node28 node30 (ThiS) -COSS -(ThiF) ThiF->node30 node28->Thil node29 (ThiS)-COSH Thil->node29 node29->ThiF ThiG node30->ThiG node36 ThiH ThiG node30->node36 node31 1-Deoxy -D-xylulose -5-phosphate node31->node36 node32 Imino-glycine node32->ThiG Tyrosine biosynthesis node33 L-Tyrosine Tyrosine biosynthesis->node33 node33->ThiG node33->node36 Glycine node34 Glycine->node34 node34->node32 ThiG->node20 node35 Glycine, serine and threonine metabolism node35->Glycine node36->node20 Cysteine and Methionine Metabolism Cysteine and Methionine Metabolism->node23 Glycolysis Glycolysis->node21 Glycolysis->Pyruvate Steroid biosynthesis Steroid biosynthesis->node31 ThiC->node2 print "