ATP-citrate lyase kinase and cyclic AMP-dependent protein kinase phosphorylate different sites on ATP-citrate lyase.

ATP-citrate lyase was phosphorylated by highly purified cyclic AMP-independent protein kinase (ATP-citrate lyase kinase) or the catalytic subunit of cyclic AMP-dependent protein kinase. Each kinase phosphorylated ATP-citrate lyase equally but the combination of both kinases increased ATP-citrate lyase phosphorylation additively. When ATP-citrate lyase was phosphorylated with each kinase and partially digested with either L-1-tosylamido-2-phenylmethyl chloromethyl ketone-treated trypsin or Staphylococcus aureus protease followed by electrophoresis of the proteolytic products on sodium dodecyl sulfate-polyacrylamide gels or when the phosphorylated lyase was completely digested by these proteases followed by chromatography and electrophoresis, the results showed that the site phosphorylated by ATP-citrate lyase kinase was different from that phosphorylated by the catalytic subunit of cyclic AMP-dependent protein kinase. Only phosphoserine was found in lyase phosphorylated by the catalytic subunit of cyclic AMP-dependent protein kinase whereas phosphoserine and phosphothreonine were found in ATP-citrate lyase phosphorylated by lyase kinase.