CAMP-Dependent Protein Kinase Activity in Yeast Mitochondria

Abstract

Two different cAMP-binding proteins have been identified in yeast mitochondria by photoaffinity labelling and based on the occurrence of cAMP-binding activity in two different sub-mitochondrial fractions. One protein (Mr 45-46,000) is tightly bound to the inner mitochondrial membrane whereas the other (Mr 42,000) is found in the soluble intermembrane space. With endogenous substrate cAMP-dependent protein kinase activity could not be demonstrated with sufficient clarity. However, using acidic heterologous substrates, like casein and phosvitin, one cAMP-dependent protein kinase was identified in the intermembrane space. Only low phosphate incorporation was found using histone fractions as substrate. cAMP-dependent modification of proteins appears to be very shortlived in mitochondria. Its physiological significance remains unknown, since neither mitochondrial transcription, translation, respiration nor import of cytoplasmically synthesized precursors into mitochondria appear to be influenced by exogenous cAMP either in vivo or in vitro. It is shown that cAMP is not actively transported into the inner mitochondrial compartment but rather binds to a receptor(s) localized outside the permeability barrier provided by the inner membrane.