Apoptosis induces efflux of the mitochondrial matrix enzyme deoxyguanosine kinase. 
Deoxyguanosine kinase (dGK) initiates the salvage of purine deoxynucleosides in mitochondria and is a key enzyme in mitochondrial DNA precursor synthesis.  The active form of the enzyme is a 60-kDa protein normally located in the mitochondrial matrix.  Here we describe the subcellular distribution of dGK during apoptosis in human epithelial kidney 293 cells and human lymphoblast Molt-4 cells.  Immunological methods were used to monitor dGK as well as other mitochondrial proteins.  Surprisingly, dGK was found to relocate to the cytosolic compartment at a similar rate as cytochrome c, a mitochondrial intermembraneous enzyme known to enter the cytosol early in apoptosis.  The redistribution of dGK from the mitochondria to the cytosol may be of importance for the activation of apoptotic purine nucleoside cofactors such as dATP and demonstrates that mitochondrial matrix proteins may selectively leak out during apoptosis.