Autophosphorylation of the catalytic subunit of cAMP-dependent protein kinase.
The catalytic subunit of cAMP-dependent protein kinase contains two stable phosphorylation sites, Thr-197 and Ser-338 (Shoji, S., Titani, K., Demaille, J. G., and Fischer, E. H. (1979) J. Biol. Chem. 254, 6211-6214). Thr-197 is very resistant to dephosphorylation and thus cannot typically be autophosphorylated in vitro once the stable subunit is formed. Ser-338 is slowly dephosphorylated and can be rephosphorylated autocatalytically. In addition to these two stable phosphorylation sites, a new site of autophosphorylation, Ser-10, was identified. Phosphorylation at Ser-10 does not have a major effect on activity, and phosphates from Ser-10 or Ser-338 are not transferred to physiological substrates such as the type II regulatory subunit. Autophosphorylation at Ser-10 is associated with one of the two major isoelectric variants of the catalytic subunit. The form having the more acidic pI can be autophosphorylated at Ser-10 while the more basic form of the catalytic subunit cannot. Phosphorylation at Ser-10 does not account for the two isoenzyme forms. Since the reason for two isoelectric variants of the catalytic subunit is still unknown, it is not possible to provide a structural basis for the difference in accessibility of Ser-10 to phosphorylation. Either Ser-10 is not accessible in the more basic form of the catalytic subunit or some other type of post- or cotranslational modification causes Ser-10 to be a poor substrate. Whether the myristoyl group at the amino-terminal Gly is important for Ser-10 autophosphorylation remains to be established. The isoenzyme forms of the catalytic subunit do not correspond to the gene products coded for by the C alpha and C beta genes.
Toner-Webb
J
J
Department of Chemistry, University of California, San Diego, La Jolla 92093-0654.
van Patten
S M
SM
Walsh
D A
DA
Taylor
S S
SS
D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D006657:Histones / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009206:Myocardium / Q000201:enzymology*; D009842:Oligopeptides / Q000378:metabolism; D010446:Peptide Fragments / Q000302:isolation & purification; D010766:Phosphorylation; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D012694:Serine; D013552:Swine; D013912:Threonine; D014357:Trypsin
D006657:Histones; D046911:Macromolecular Substances; D009842:Oligopeptides; D010446:Peptide Fragments; D013912:Threonine; D012694:Serine; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D014357:Trypsin