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The glucokinase regulatory protein (GKRP) also known as glucokinase (hexokinase 4) regulator (GCKR) is a protein produced in hepatocytes (liver cells). GKRP binds and moves glucokinase (GK), thereby controlling both activity and intracellular location of this key enzyme of glucose metabolism. GKRP is a 68 kD protein of 626 amino acids. It is coded for by a 19 exon gene, ''GCKR'', on the short arm of chromosome 2 (2p23). GKRP was discovered by Emile van Schaftingen and reported in 1989 == Physiological function == Glucokinase (GK) in liver cells phosphorylates glucose, preparing it for incorporation into glycogen. During periods of ample glucose supply, most GK activity can be found in the peripheral cytoplasm where glycogen synthesis is occurring. As the glucose supply declines during periods of fasting, GK activity in the cytoplasm diminishes. GKRP participates in this modulation of GK activity and location by binding free cytoplasmic GK as glucose levels decline, and moving it into the nucleus, where it is held in reserve in an inactive form. As glucose and insulin levels rise, as during digestion of a meal, GK is released from GKRP and moves back to the cytoplasm, where much of it associates with the bifunctional enzyme. In hepatocytes of various mammals, GKRP has always been found in molar excess of the amount of GK, but the GKRP:GK ratio varies according to diet, insulin sufficiency, and other factors. Free GKRP shuttles between the nucleus and the cytoplasm. It may be attached to the microfilament cytoskeleton. GKRP competes with glucose to bind with GK, but inactivates it when bound. In conditions of low glucose, GKRP then pulls the GK into the nucleus. Rising amounts of glucose coming into the hepatocyte prompt the GKRP to rapidly release GK to return to the cytoplasm. GKRP itself is subject to modulation. Fructose and sorbitol can both be converted to fructose-1-phosphate, which inhibits GKRP and frees GK.〔 Fructose 6-phosphate binds to the same site of GKRP, but enhances the ability of GKRP to bind and inactivate GK. In contrast, phosphorylation of GKRP by AMP-activated protein kinase, induced by elevated levels of AMP, reduces its capacity to inactivate GK. 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「Glucokinase regulatory protein」の詳細全文を読む スポンサード リンク
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