Phosphorylation of phosphoenolpyruvate carboxykinase (PEPCK) and phosphoenolpyruvate carboxylase (PEPC) in the flesh of fruits

• This study determined whether PEPCK and PEPC are phosphorylated in the flesh of fruits.
• This was done by incubating fruit flesh with 32Pi.
• Both enzymes were phosphorylated in vivo in the flesh of grape, tomato, cherry, and plum.
• PEPCK was also phosphorylated in vivo in developing grape seeds.

This study determined whether phosphoenolpyruvate carboxykinase (PEPCK) and phosphoenolpyruvate carboxylase (PEPC) are phosphorylated in the flesh of a range of fruits. This was done by incubating fruit flesh with 32P[P] (where 32P[P] = 32PO43−), then PEPCK and PEPC were immunoprecipitated from extracts using specific antisera. The incorporation of 32P[P] into these enzymes was then determined by autoradiography of SDS-PAGE gels. Both enzymes were subject to phosphorylation in vivo in the flesh of grape, tomato, cherry and plum. PEPCK was also subject to phosphorylation in vivo in developing grape seeds. Proteolytic cleavage of PEPCK showed that it was phosphorylated at a site(s) located on its N-terminal extension. Potentially phosphorylation of these enzymes could contribute to the coordinate regulation of their activities in the flesh of fruits and in developing seeds.