Phosphoenolpyruvate carboxykinase [GTP], mitochondrial
phosphoenolpyruvate carboxykinase (GTP) activity
Kinetic and functional properties of human mitochondrial phosphoenolpyruvate carboxykinase.
The cytosolic form of phosphoenolpyruvate carboxykinase (PCK1) plays a regulatory role in gluconeogenesis and glyceroneogenesis. The role of the mitochondrial isoform (PCK2) remains unclear. We report the partial purification and kinetic and functional characterization of human PCK2. Kinetic properties of the enzyme are very similar to those of the cytosolic enzyme. PCK2 has an absolute requirement for Mn<sup>2+</sup> ions for activity; Mg<sup>2+</sup> ions reduce the K<sub>m</sub> for Mn<sup>2+</sup> by about 60 fold. Its specificity constant is 100 fold larger for oxaloacetate than for phosphoenolpyruvate suggesting that oxaloacetate phosphorylation is the favored reaction <i>in vivo</i>. The enzyme possesses weak pyruvate kinase-like activity (k<sub>cat</sub>=2.7 s<sup>-1</sup>). When overexpressed in HEK293T cells it enhances strongly glucose and lipid production showing that it can play, as the cytosolic isoenzyme, an active role in glyceroneogenesis and gluconeogenesis.