Occurrence of A-kinase anchor protein and associatedcAMP-dependent protein kinase in the inner compartmentof mammalian mitochondria

Evidence showing the existence in the inner compartment of rat-heart mitochondria of AKAP121 and associated PKA is presented. Immunoblotting analysis and trypsin digestion pattern show that 90% or more of mitochondrial C-PKA, RPKA and AKAP121 is localized in the inner mitochondrial compartment, when prepared both from isolated mitochondria or cardiomyocyte cultures. This localization is verified by measurement of the specific catalytic activity of PKA, radiolabelling of R-PKA by 32P-phosphorylated C-PKA and of AKAP by 32Pphosphorylated R-PKA and electron microscopy of mitochondria exposed to gold-conjugated AKAP121 antibody.