A Common Phosphorylation Site for Cyclic AMP-dependent Protein Kinase and Protein Kinase C in Human Placental 6-Phosphofructo-2-kinase/Fructose-2,6-bisphosphatase

Abstract

  Human placental 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (HP2K) was phosphorylated by incubation with [γ-³²P]MgATP and cyclic AMP-dependent protein kinase (PKA) or protein kinase C (PKC). Approximately 0.8 mol of phosphate per mol subunit of HP2K was incorporated by either PKA or PKC. However, with additional incubation with PKA following incubation with PKC or vice versa, no additional phosphate was incorporated into the HP2K. The phosphorylation sites for the two protein kinases were identified by peptide mapping and microsequencing following digestion of phosphorylated-HP2K with clostripain. Evidence is also suggested for a common phosphorylation site (Ser-460) for PKA and PKC.