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TPI1
Triosephosphate isomerase is an enzyme that in humans is encoded by the ''TPI1'' gene.
This gene encodes an enzyme, consisting of two identical proteins, which catalyzes the isomerization of glyceraldehydes 3-phosphate (G3P) and dihydroxy-acetone phosphate (DHAP) in glycolysis and gluconeogenesis. Mutations in this gene are associated with triosephosphate isomerase deficiency. Pseudogenes have been identified on chromosomes 1, 4, 6 and 7. Alternative splicing results in multiple transcript variants.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=7167 )〕
== Structure ==
Triose Phosphate Isomerase is a member of the alpha and beta (α/β) class of proteins; it is a homodimer, and each subunit contains 247 amino acids. Each TPI1 monomer contains the full set of catalytic residues, but the enzyme is only active in the oligomeric form. Therefore, the enzyme must be in a dimer in order to achieve full function of the enzyme, even though it is not believed that the two active sites participate in cooperativity with each other. Each subunit contains 8 exterior alpha helices surrounding 8 interior beta strands, which form a conserved structural domain called a closed alpha/beta barrel (αβ) or more specifically a TIM barrel. Characteristic of most all TIM barrel domains is the presence of the enzyme's active site in the lower loop regions created by the eight loops that connect the C-termini of the beta strands with the N-termini of the alpha helices. TIM barrel proteins also share a structurally conserved phosphate binding motif, with the phosphate group found in the substrate or cofactors.〔
In each chain, nonpolar amino acids pointing inward from the beta strands contribute to the hydrophobic core of the structure. The alpha helices are amphipathic: their outer (water-contacting) surfaces are polar, while their inner surfaces are largely hydrophobic.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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