The mitochondrial isoform of chicken liver PEPCK complexed with Mn2+, Mn2+-phosphoenolpyruvate (PEP), and Mn2+-GDP provides information about its structure and how this enzyme catalyzes reactions.

As the first committed step in gluconeogenesis, PEPCK decarboxylates and phosphorylates oxaloacetate (OAA) for its conversion to PEP, when GTP is present.

[10] When pyruvate kinase – the enzyme that normally catalyzes the reaction that converts PEP to pyruvate – is knocked out in mutants of Bacillus subtilis, PEPCK participates in one of the replacement anaplerotic reactions, working in the reverse direction of its normal function, converting PEP to OAA.

The enzyme has therefore been thought to be essential in glucose homeostasis, as evidenced by laboratory mice that contracted diabetes mellitus type 2 as a result of the overexpression of PEPCK-C.[14] The role that PEPCK-C plays in gluconeogenesis may be mediated by the citric acid cycle, the activity of which was found to be directly related to PEPCK-C abundance.

[15] While the mouse liver almost exclusively expresses PEPCK-C, humans equally present a mitochondrial isozyme (PEPCK-M).

The blood glucose level is maintained within well-defined limits in part due to precise regulation of PEPCK gene expression.

Glucagon indirectly elevates the expression of PEPCK-C by increasing the levels of cAMP (via activation of adenylyl cyclase) in the liver which consequently leads to the phosphorylation of S133 on a beta sheet in the CREB protein.

[3] A collaborative study between the U.S. Environmental Protection Agency (EPA) and the University of New Hampshire investigated the effect of DE-71, a commercial PBDE mixture, on PEPCK enzyme kinetics and determined that in vivo treatment of the environmental pollutant compromises liver glucose and lipid metabolism possibly by activation of the pregnane xenobiotic receptor (PXR), and may influence whole-body insulin sensitivity.

PEPCK decarboxylates the bundle sheath oxaloacetate, releasing carbon dioxide, which is then fixed by the enzyme Rubisco.

[21] PEPCK of Mycobacterium tuberculosis has been shown to trigger the immune system in mice by increasing cytokine activity.

Transcription of the PEPCK-C gene is stimulated by glucagon, glucocorticoids, retinoic acid, and adenosine 3',5'-monophosphate (cAMP), while it is inhibited by insulin.

[24] Of these factors, insulin, a hormone that is deficient in the case of type 1 diabetes mellitus, is considered dominant, as it inhibits the transcription of many of the stimulatory elements.

[25] In prolonged acidosis, PEPCK-C is upregulated in renal proximal tubule brush border cells, in order to secrete more NH3 and thus to produce more HCO3−.

[10] As discussed previously, PEPCK abundance increased when plants were watered with low-pH ammonium chloride, though high pH did not have this effect.