The Phospho-PKA RII alpha (Ser99) antibody detects the phosphorylated form of the regulatory subunit RIIα of cAMP-dependent protein kinase (PKA) at serine 99. PKA, a central kinase in cAMP signaling, consists of two regulatory (R) and two catalytic (C) subunits. The R subunits (RIα, RIβ, RIIα, RIIβ) maintain PKA in an inactive state until cAMP binding triggers dissociation and activation of C subunits. RIIα, encoded by PRKAR2A, localizes PKA to specific subcellular compartments via A-kinase anchoring proteins (AKAPs), ensuring spatial-temporal signaling precision. Phosphorylation of RIIα at Ser99 occurs through autophosphorylation or other kinases, modulating PKA holoenzyme stability, AKAP interactions, or feedback regulation. This post-translational modification is implicated in cellular responses to cAMP fluctuations, such as metabolic regulation, stress adaptation, and cell cycle progression. The Phospho-PKA RII alpha (Ser99) antibody is widely used in studies investigating cAMP/PKA pathway dynamics, particularly in contexts like cardiovascular function, neuronal signaling, and cancer, where aberrant PKA activity is linked to disease. Its specificity for the phosphorylated epitope makes it a critical tool for assessing RIIα activation status and dissecting mechanisms underlying PKA-dependent signaling networks.