Isolation and properties of the bovine brain protein inhibitor of adenosine 3′:5′‐monophosphate‐dependent protein kinases

While the heat-stable protein inhibitor (PKI) of the CAMP-dependent protein kinase was first described in skeletal muscle [I] from which it was recently isolated in pure form [2] , its greatest concentration occurs in the brain [3] . This is not surprising in view of the very high concentration of protein kinase found in this tissue It has recently been proposed that CAMP-dependent phosphorylations might be involved in neuronal functions, such as tissue growth, membrane permeability and synaptic transmission (reviewed [S-7] ). Another protein kinease inhibitor has also been described in nervous tissue that can block phosphorylations catalyzed by both cyclic nucleotidedependent and -independent enzymes [8].