What is released when cAMP binds to the regulatory subunits of PKA?

When cAMP binds to the regulatory subunits of protein kinase A (PKA), it triggers a conformational change that leads to the release of the active catalytic subunits. Under resting conditions, PKA exists as a holoenzyme composed of two regulatory and two catalytic subunits. The binding of cAMP to the regulatory subunits causes them to dissociate from the catalytic subunits, effectively activating the catalytic portion of the enzyme.

This activation allows the catalytic subunits to phosphorylate various target proteins, thus propagating the cellular response to signals like hormones and other stimuli. The process is crucial as it links extracellular signals to intracellular responses, enabling a wide range of physiological processes. Understanding this mechanism is key in the study of signal transduction pathways and their regulation in cellular activities.