Glucose-6-phosphatase (G6PC) associated with the inner face of the endoplasmic reticulum membrane catalyzes the hydrolysis of glucose-6-phosphate to glucose and orthophosphate. This reaction is essentially irreversible (Lei et al. 1993, Ghosh et al. 2002). Defects in glucose-6-phosphatase are the cause of glycogen storage disease type 1a (Lei et al. 1993, 1995, Chou and Mansfield 2008).