Protein Kinase A
Protein kinases are enzymes which catalyse the phosphorylation of proteins. ATP often supplies the phosphate for the reaction. Protein kinases have differing levels of specificity. Some will only phosphorylate one particular protein but others, such as protein kinase A, can phosphorylate many different proteins. Protein kinase A is involved in the ‘fight or flight’ response in mammals. In this response, the hormone adrenaline causes the production of cyclic AMP, a secondary messenger. Cyclic AMP then activates protein kinase A. Protein kinase A then activates phosphorylase kinase which continues the pathway for the breakdown of glycogen. This pathway occurs in the muscle and in the liver but the hormone is glucagon in the liver.