Identification of the phosphorylated sites of phosphofructokinase from skeletal muscle after in vivo and in vitro phosphorylation.

Phosphofructokinase from mice muscle was radioactively labelled either in vivo by the injection of [³²P]-phosphate or in vitro by the incubation with cAMP-dependent protein kinase and [γ-³²P]-ATP. Two labelled peptides were obtained after tryptic digestion in either case showing that at least two sites were phosphorylated. Independent of the labelling method, the labelled peptides showed an analogous pattern on the peptide maps, indicating that both methods led to the phosphorylation of the same sites.