Definition for Protein kinase A

From Biology Forums Dictionary

Protein kinase A (PKA) is a versatile regulator of cell metabolism and gene transcription and consists of two main subunits, PKAc and PKAR (PKAR is the regulatory subunit of PKA). Before cellular activation, PKAc and PKAR bind in an inactive complex that can be induced by the low molecular weight signaling molecule cAMP. Cyclic AMP is a second messenger molecule generated both at the cell surface and in the cytoplasm by numerous isoforms of the enzyme adenylate cyclase. Binding of cAMP to the PKA complex liberates PKAc to interact with a wide range of protein substrates, phosphorylating them on serine or threonine residues, usually within the conserved motif (RXXS/T), (where X can be any amino acid, R is arginine, S/T serine or threonine).