Evidence for the existence of phosphoenolpyruvate carboxykinase ferroactivator activity in adult and fetal guinea pigs.

Newborn (24--72 h) guinea pig liver cytosolic phosphoenolpyruvate carboxykinase (PEPCK) activity is increased by incubation of the cytosol with the metal salts FeCl2, MnCl2, CoCl2 and CdCl2. FeCl2 at 30 micromol/l concentration is the most effective activator causing a 3.5-fold increase in activity. Purified rat liver cytosolic PEPCK is activated by 30 mumol/l FeCl2 in the presence of liver cytosol of fetal and newborn guinea pigs. These results confirm the existence of PEPCK ferroactivator in the guinea pig which has properties similar to the one found in rat liver. The tissue distribution of ferroactivator activity parallels that of cytosolic PEPCK, being highest in the gluconeogenic organs liver and kidney. Hepatic PEPCK ferroactivator activity can be demonstrated by day 45 of gestation, increasing linearly in specific activity to adult levels at term (65 days). The distribution and development of the ferroactivator is consistent with the hypothesis that it may play a role in the physiologic control of PEPCK.