Development of phosphoenolpyruvate carboxykinase ferroactivator in fetal and young rats and guinea pigs.

The development of ferroactivator, a protein that permits Fe2+ to activate the gluconeogenic enzyme phosphoenolpyruvate carboxykinase, was compared to that of the carboxykinase in rat and guinea pig fetuses and neonates. Significant ferroactivator was present in the liver of the fetal rat and in the liver and kidney of the fetal guinea pig in the last half of gestation. The development of ferroactivator does not parallel that of the carboxykinase which does not attain maximal levels until after birth. Thus, the ferroactivator cannot be rate limiting for neonatal gluconeogenesis. It was found, unexpectedly, that the carboxykinase was increased during suckling in the guinea pig.