title: Insulin action rapidly decreases multifunctional protein kinase activity in rat adipose tissue.
abstract: ATP-citrate lyase in vivo contains three phosphorylation sites on two tryptic peptides (peptides A and B). These phosphorylation sites are under hormonal control. Multifunctional protein kinase (MFPK) from rat liver phosphorylates peptide B on serine and threonine residues whereas cAMP-dependent protein kinase phosphorylates peptide A on a serine residue (Ramakrishna, S., and Benjamin, W. B. (1985) J. Biol. Chem. 260, 12280-12286). We now report that rat adipose tissue MFPK also phosphorylates serine and threonine residues of peptide B of ATP-citrate lyase. When the activity of MFPK was assayed using partially purified (by chromatography on phosphocellulose) cytosol fractions from insulin-treated adipose tissue, it was found that MFPK activity was decreased by over 55%. This decrease in MFPK activity occurs at physiological concentrations of insulin (EC50 = 1 x 10(-10) M). Its onset is rapid and almost maximal at 5 min after the addition of insulin. Even when new protein synthesis is inhibited by cycloheximide, extracts from insulin-treated fat pads have less MFPK activity compared to the control. The insulin effect is maintained after further chromatography on a gel filtration column suggesting that the decrease in MFPK activity is not due to a low molecular weight inhibitor. The insulin-induced decrease in MFPK activity is due to a decrease in Vmax whereas the affinity of this enzyme toward ATP-citrate lyase or ATP is unchanged.
mesh_terms: D001275:ATP Citrate (pro-S)-Lyase / Q000378:metabolism; D000273:Adipose Tissue / Q000187:drug effects / Q000201:enzymology*; D000818:Animals; D002845:Chromatography; D002851:Chromatography, High Pressure Liquid; D003513:Cycloheximide / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D010446:Peptide Fragments / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D047428:Protein Kinase Inhibitors; D051381:Rats; D011919:Rats, Inbred Strains; D014357:Trypsin / Q000378:metabolism
chemical_list: D007328:Insulin; D010446:Peptide Fragments; D047428:Protein Kinase Inhibitors; D010769:Phosphothreonine; D010768:Phosphoserine; D003513:Cycloheximide; D001275:ATP Citrate (pro-S)-Lyase; D014357:Trypsin