An insulin-sensitive cytosolic protein kinase accounts for the regulation of ATP citrate-lyase phosphorylation.
Purified rat liver ATP citrate-lyase is phosphorylated on serine residues by an insulin-stimulated cytosolic kinase activity partially purified from rat adipocytes [Yu, Khalaf & Czech (1987) J. Biol. Chem. 262, 16677-16685]. The Km for lyase phosphorylation by this hormone-sensitive kinase activity is approx. 3 microM. Two-dimensional tryptic-peptide mapping of the 32P-labelled lyase reveals that the kinase-catalysed phosphorylation occurs primarily on a specific peptide. In intact 32P-labelled adipocytes, insulin enhances the serine phosphorylation of ATP citrate-lyase by 2-3-fold. Tryptic digestion of the 32P-labelled lyase immunopurified from insulin-treated adipocytes also yields one major phosphopeptide. 32P-labelled lyase tryptic peptides derived from labelling experiments in vitro and in vivo exhibit identical electrophoretic and chromatographic migration profiles. Furthermore, radio-sequencing of the phosphopeptide from lyase 32P-labelled in vitro indicates that serine-3 from the N-terminus is phosphorylated by the insulin-stimulated cytosolic kinase, in agreement with previous studies on the position of the phosphoserine residue in ATP citrate-lyase isolated from insulin-treated cells. Taken together, the similarity in site-specific phosphorylation of ATP citrate-lyase from insulin-treated adipocytes to that catalysed by the hormone-activated cytosolic kinase in vitro strongly suggests that this kinase mediates insulin action on lyase phosphorylation in intact cells.
Yu
K T
KT
Department of Physiology and Biophysics, School of Medicine, State University of New York, Stony Brook 11794.
Benjamin
W B
WB
Ramakrishna
S
S
Khalaf
N
N
Czech
M P
MP
D001275:ATP Citrate (pro-S)-Lyase / Q000378:metabolism*; D000273:Adipose Tissue / Q000166:cytology / Q000201:enzymology; D000818:Animals; D004822:Epididymis / Q000201:enzymology; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D010446:Peptide Fragments / Q000378:metabolism; D010449:Peptide Mapping; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012694:Serine / Q000378:metabolism
D007328:Insulin; D010446:Peptide Fragments; D012694:Serine; D001275:ATP Citrate (pro-S)-Lyase; D011494:Protein Kinases