In animals, this is a rate-controlling step of gluconeogenesis, the process by which cells synthesize glucose from metabolic precursors. The blood glucose level is maintained within well-defined limits in part due to precise regulation of PEPCK gene expression. To emphasize the importance of PEPCK in glucose homeostasis, over expression of this enzyme in mice results in symptoms of type II diabetes mellitus, by far the most common form of diabetes in humans. Due to the importance of blood glucose homeostasis, a number of hormones regulate a set of genes (including PEPCK) in the liver that modulate the rate of glucose synthesis.