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Glucose-1,6-bisphosphate synthase is a type of enzyme called a phosphotransferase and is involved in mammalian starch and sucrose metabolism (KEGG, (2.7.1.106 )). It catalyzes the transfer of a phosphate group from 1,3-bisphosphoglycerate to glucose-1-phosphate, yielding 3-phosphoglycerate and glucose-1,6-bisphosphate. (image courtesy of the BRENDA enzyme database) The enzyme requires a divalent metal ion cofactor. Zinc 2+, Magnesium 2+, Manganese 2+, Calcium 2+, Nickel 2+, Copper 2+, Cadmium 2+ are all proven effective cofactors. Additionally, the enzyme appears to function optimally in a pH range from 7.3-8.7 and at a temperature of 25 degrees Celsius.〔 ==Metabolic significance of the catalyzed reaction== The main product, glucose-1,6-bisphosphate, appears to have several functions: 1. inhibition of hexokinase, an enzyme used in the first step of glycolysis. 2. activation of phosphofructokinase-1 (PFK-1) and pyruvate kinase, both of which are enzymes involved in activation of the glycolytic pathway.〔 3. acts as a coenzyme for phosphoglucomutase in glycolysis and gluconeogenesis. 4. acts as a cofactor for phosphopentomutase, which produces D-ribose-5-phosphate.〔 〕 5. acts as a phosphate donor molecule for unknown nonmetabolic effector proteins.〔 6. increases in concentration during skeletal muscle contraction. 7. dephosphorylation yields glucose-6-phosphate, which is an important precursor molecule in glycolysis and the pentose phosphate pathway. Glucose-1,6-bisphosphate is most likely used in correlation with gluconeolysis. The product’s inhibition of hexokinase and activation of PFK-1 and pyruvate kinase is indicative of its role in glycolysis. Glucose-1,6-bisphosphate inhibit hexokinase stopping the production glucose-6-phosphate from D-glucose. Its activation of PFK-1 and pyruvate kinase shows that glycolysis still continues without the production of glucose-6-phosphate from D-glucose. This means that the glucose-6-phosphate needed for glycolysis most likely comes from gluconeolysis. The reactant glucose-1-phosphate is produced by gluconeolysis. This reactant can also form D-glucose-6-phosphate, which is needed for glycolysis. It can therefore be inferred that it is possible when glucose-1-phosphate is produced, it makes glucose-1,6-bisphosphate (with glucose-1,6-bisophosphate synthase) and glucose-6-phosphate. The glucose-1,6-bisphosphate increase the activity of glycolysis, of which glucose-6-phosphate is a reagent. In addition, one of the reactants (1,3-bisphosphoglycerate) and one of the products (3-phosphoglycerate) are intermediates in the 'payoff' phase of glycolysis. In other words, two molecules involved with glucose-1,6-bisphosphate synthase are able to be both created and recycled in the glycolytic pathway. The reactant glucose 1-phosphate is an important precursor molecule in many different pathways, including glycolysis, gluconeogenesis and the pentose phosphate pathway. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Glucose-1,6-bisphosphate synthase」の詳細全文を読む スポンサード リンク
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