ABSTRACT
PKA assembles as a holoenzyme formed by a dimer of two R subunits that each binds a C subunit. Type I holoenzymes contain homodimers of RIα or RIβ subunits, although it is likely that heterodimers of RIα/RIβ can sometimes also form. Dissociation of type I holoenzymes occurs at a lower threshold of cAMP compared with type II holoenzymes containing homodimers of RIIα or RIIβ. The RIβ containing holoenzyme is more sensitive to cAMP-induced dissociation compared with RIα containing holoenzymes. One of the major differences between type I and type II holoenzymes is their subcellular localization and this is determined by interaction with A kinase anchoring proteins (AKAPs), which generally have a much greater afnity for the type II holoenzymes as discussed in the following section.
