PHOSPHORYLATION OF ATP-CITRATE LYASE BY NUCLEOSIDE DIPHOSPHATE KINASE

Rat liver nucleoside diphosphate kinase (NDPK) and PC12 cell cytosol were used to determine whether NDPK could function as a protein kinase. NDPK was phosphorylated on its catalytic histidine using [gamma-P-32]ATP, and the phosphorylated NDPK separated from [gamma-P-32]ATP, The addition of phosphorylated NDPK to dialyzed PC12 cell cytosol resulted in the phosphorylation of a protein with a subunit molecular mass of about 120 kDa, This phosphorylation appeared to occur by a direct transfer of a phosphoryl group from the catalytic histidine of NDPK to a histidine on the 120-kDa protein. The 120-kDa protein was partially purified and shown by peptide sequencing to be ATP-citrate lyase, ATP-citrate lyase is the primary source of cytosolic acetyl-CoA. NDPK phosphorylated the histidine at the catalytic site of ATP-citrate lyase, This histidine can also be phosphorylated by ATP, and its phosphorylation is the first step in the conversion of citrate and CoA to oxaloacetate and acetyl-CoA by ATP-citrate lyase. The level of phosphorylation of PC12 cell ATP-citrate lyase by phosphorylated NDPK was comparable with that by ATP. Thus, in addition to its nucleoside diphosphate kinase activity, NDPK can function as a protein kinase.