Which of the following events does not occur when concentration of glucose in the liver decreases:
C i.e. Increased levels of Fructose 2, 6 - Bisphosphate- Decreased concentration of glucose in blood & liver causes increased glucagon secretion (ki glucagon / insulin ratio) leading to glycogenolysis followed by gluconeogenesis in liver. Increased levels of glucagon activates c-AMP dependent protein kinase which inturn activates F2, 6 BPase (fructose 2, 6 biphosphatase or FBpase 2) and inactivates phosphofructokinase (PFK)-2 leading to conversion of F2, 6 BP (Fructose 2, 6 biphosphatse) to fructose 6 phosphate. So the concentration of F2, 6 BP is decreasedQ and fructose 6 phosphate is increased which is conveed to glucose.- Gluconeogenesis in fasting state is indicated by acetyl CoA induced instantaneous allosteric activation of hepatic pyruvate carboxylase.- Phosphofructokinase I takes pa in glycolysis and FBPase 1 in gluconeogenesis, by catalyzing the formation & breakdown of fructose 1, 6 biphosphate respectively. Whereas bifunctional enzyme phosphor fructo kinase 2 (PK-2) also has fructose 2, 6 biphosphatase (FBP ase 2 or F 2, 6 pase) activity and plays a unique role in regulation of both glycolysis & gluconeogenesis by determining the levels of fructose 2, 6 bihosphateQ.- Fructose 2, 6 bihosphate (F2, 6BP) is the most potent allosteric activator of PFK-1 (thereby increase glycolysis) and inhibitor of fructose 1, 6 biphosphatase /FBP ase 1/ Fl, 6 pase (thereby decreasing gluconegenesis) in liverQ. The reciprocal action of fructose 2, 6 biPO4, on glycolysis and gluconeogenesis ensure that both pathways, is not fully active at same time. Therefore, decreased sensitivity of FBP ase 1 to regulation (inhibition) by fructose 2, 6 biphosphate increases gluconeogenesis; thereby decreasing levels of fructose 1, 6 biphosphate, pyruvate and ATPQ.- Fructose 1, 6 biphosphate is under negative feed back control of fructose 2, 6 biphosphateQ. If fructose 1, 6 biphasphatase becomes less sensitive to the negative feed back of fructose 2, 6 biPO4, its level of activity will increase. Thus more fructose 1, 6 biPO4 will be cleaved into fructose 6-PO4 and levels of fructose 1, 6 biPO4 will decrease and be lower than normal. The cycle will be shifted more toward gluconeogenesis. Less ATP would be generated Wt decreased glycolysisQ.Glycogenic capability of cell is determined by presence (activation) of fructose 1, 6 biphosphataseQ. The conversion of fructose 1, 6-bisphosphate to fructose6-phosphate, to achieve a reversal of glycolysis, is catalyzed by fructose-1,6-bisphosphatase. Its presence determines whether or not a tissue is capable of synthesizing glycogen not only from pyruvate but also from triosephosphates. It is present in liver, kidney, and skeletal muscle but is probably absent from hea and smooth muscle. In well fed state gluconeogenesis in liver is inhibited by ADPQ.
Inactivation of phosphofructokinase-2 (PFK-2)
Activation of Fructose Bisphosphatase-2 (Fructose 2, 6 Bisphosphatase)
Increased levels of Fructose 2, 6 - Bisphosphate
Increased levels of Glucagon