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Liver cells express the transmembrane enzyme glucose 6-phosphatase in the endoplasmic reticulum. The catalytic site is found on the lumenal face of the membrane, and removes the phosphate group from glucose 6-phosphate produced during glycogenolysis or gluconeogenesis.
The enzyme glucose 6-phosphatase (EC 3.1.3.9, G6Pase; systematic name D-glucose-6-phosphate phosphohydrolase) catalyzes the hydrolysis of glucose 6-phosphate, resulting in the creation of a phosphate group and free glucose:
Glucose-6-phosphate dehydrogenase (G6PD) is an enzyme in the pentose phosphate pathway (see image, also known as the HMP shunt pathway). G6PD converts glucose-6-phosphate into 6-phosphoglucono-δ-lactone and is the rate-limiting enzyme of this metabolic pathway that supplies reducing energy to cells by maintaining the level of the reduced form ...
G6PD converts G6P into 6-phosphoglucono-δ-lactone and is the rate-limiting enzyme of the pentose phosphate pathway. Thus, regulation of G6PD has downstream consequences for the activity of the rest of the pentose phosphate pathway. Glucose-6-phosphate dehydrogenase is stimulated by its substrate G6P.
Once glucose enters the cell, the first step is phosphorylation of glucose by a family of enzymes called hexokinases to form glucose 6-phosphate (G6P). This reaction consumes ATP, but it acts to keep the glucose concentration inside the cell low, promoting continuous transport of blood glucose into the cell through the plasma membrane transporters.
Here, glycogen phosphorylase cleaves the bond linking a terminal glucose residue to a glycogen branch by substitution of a phosphoryl group for the α[1→4] linkage. [1] Glucose-1-phosphate is converted to glucose-6-phosphate (which often ends up in glycolysis) by the enzyme phosphoglucomutase. [1]
Glucose-6-phosphate dehydrogenase is the rate-controlling enzyme of this pathway [citation needed]. It is allosterically stimulated by NADP + and strongly inhibited by NADPH . [ 7 ] The ratio of NADPH:NADP + is the primary mode of regulation for the enzyme and is normally about 100:1 in liver cytosol [ citation needed ] .
Glucose-6-phosphatase, catalytic subunit (glucose 6-phosphatase alpha) is an enzyme that in humans is encoded by the G6PC gene. [5] [6]Glucose-6-phosphatase is an integral membrane protein of the endoplasmic reticulum that catalyzes the hydrolysis of D-glucose 6-phosphate to D-glucose and orthophosphate.