title: Substrate enhances the sensitivity of type I protein kinase a to cAMP.
abstract: The functional significance of the presence of two major (types I and II) isoforms of the cAMP-dependent protein kinase (PKA) is still enigmatic. The present study showed that peptide substrate enhanced the activation of PKA type I at low, physiologically relevant concentrations of cAMP through competitive displacement of the regulatory RI subunit. The effect was similar whether the substrate was a short peptide or the physiological 60-kDa protein tyrosine hydroxylase. In contrast, substrate failed to affect the cAMP-sensitivity of PKA type II. Size exclusion chromatography confirmed that substrate acted to physically enhance the dissociation of the RIalpha and Calpha subunits of PKA type I, but not the RIIalpha and Calpha subunits of PKA type II. Substrate availability can therefore fine-tune the activation of PKA type I by cAMP, but not PKA type II. The cAMP-dissociated RII and C subunits of PKA type II reassociated much faster than the PKA type I subunits in the presence of substrate peptide. This suggests that only PKA type II is able to rapidly reverse its activation after a burst of cAMP when exposed to high substrate concentration. We propose this as a possible reason why PKA type II is preferentially found in complexes with substrates undergoing rapid phosphorylation cycles.
authors.affiliation: Department of Biomedicine, Section for Anatomy and Cell Biology, University of Bergen, Jonas Lies Vei 91, N-5009 Bergen and Haukeland University Hospital, N-5021 Bergen, Norway.
authors.forename: Kristin
authors.initials: K
authors.lastname: Viste
authors.forename: Reidun K
authors.initials: RK
authors.lastname: Kopperud
authors.forename: Anne E
authors.initials: AE
authors.lastname: Christensen
authors.forename: Stein O
authors.initials: SO
authors.lastname: Døskeland
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000378:metabolism; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D007527:Isoenzymes; D009842:Oligopeptides; D010455:Peptides; D047428:Protein Kinase Inhibitors; D021122:Protein Subunits; D000244:Adenosine Diphosphate; C037642:kemptide; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases