Control of endogenous phosphorylation of the major cAMP-dependent protein kinase substrate in adipocytes by insulin and beta-adrenergic stimulation
- National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD (USA)
In isolated, 32Pi-loaded, rat adipocytes, we have examined phosphorylation of the major cAMP-dependent protein kinase (A-kinase) substrate, a protein that appears to be associated with the lipid storage droplet and migrates in sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a 65-67-kDa doublet. In control cells, a strong phosphorylation signal is detected as the (+/- cAMP) A-kinase activity ratio ranges from approximately 0.1 to approximately 0.3-0.4 with increasing isoproterenol concentrations. By contrast, insulin-treated cells exhibiting A-kinase activity ratios over the range of 0.1-0.25 contain less 32P in the 65-67-kDa protein than control cells exhibiting identical A-kinase activity ratios. At higher activity ratios (greater than 0.3), this reduction in phosphorylation of the 65-67-kDa protein by insulin disappears. It is concluded that insulin stimulates a phosphatase activity that acts on the 65-67-kDa protein. Insulin actions aside, these studies reveal two interesting phenomena. (1) Whereas elevated, steady-state A-kinase activities are established rapidly (1-2 min) upon isoproterenol stimulation, phosphorylation of the 65-67-kDa substrate proceeds through a burst, followed by a decline to a steady-state level by 10-12 min. An adaptation mechanism, providing for a constant response to a constant stimulus, may underlie this lack of parallelism between the time course of phosphorylation and A-kinase activity. (2) Removal of (32Pi) orthophosphate immediately before isoproterenol stimulation leads to a rapid (t approximately 10 min) loss in labeling of the 65-67-kDa protein, whereas the phosphorylation state of other phosphoproteins are not changed. These data suggest that elevation of A-kinase activity leads to a rapid exchange of external Pi with an ATP pool that is used by A-kinase.
- OSTI ID:
- 6073501
- Journal Information:
- Journal of Biological Chemistry; (USA), Vol. 265:31; ISSN 0021-9258
- Country of Publication:
- United States
- Language:
- English
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INSULIN
BIOCHEMICAL REACTION KINETICS
PHOSPHOTRANSFERASES
ENZYME ACTIVITY
PROTEINS
PHOSPHORYLATION
SYMPATHOMIMETICS
AMP
ATP
ELECTROPHORESIS
FAT CELLS
PHOSPHORUS 32
RATS
SUBSTRATES
TRACER TECHNIQUES
ANIMAL CELLS
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CHEMICAL REACTIONS
CONNECTIVE TISSUE CELLS
DAYS LIVING RADIOISOTOPES
DRUGS
ENZYMES
HORMONES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIGHT NUCLEI
MAMMALS
NUCLEI
NUCLEOTIDES
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PEPTIDE HORMONES
PHOSPHORUS ISOTOPES
PHOSPHORUS-GROUP TRANSFERASES
RADIOISOTOPES
REACTION KINETICS
RODENTS
SOMATIC CELLS
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VERTEBRATES
550201* - Biochemistry- Tracer Techniques