GTP, a nonsubstrate of ATP citrate lyase, is a phosphodonor for the enzyme histidine autophosphorylation.

ATP citrate lyase (EC 4.3.1.8.) was shown to be a major phosphorylation protein of a fraction derived from Zajdela rat hepatoma by chromatography on heparin-Ultrogel, after the incubation with [gamma-32P]ATP or [gamma-32P]GTP. Histidine was the only amino acid in the purified enzyme phosphorylated by [gamma-32P]ATP or [gamma-32P]GTP in the autocatalytic reaction which occurred apparently through an intramolecular mechanism regardless of a donor of phosphate. GTP inhibits the ATP-dependent autophosphorylation competitively despite its failure to replace ATP in the formation of acetyl-CoA catalyzed by this enzyme.