Ribonucleotide reductase: evidence for specific association with HeLa cell mitochondria

Mammalian mitochondria contain pools of deoxyribonucleoside 5'-triphosphates that behave differently from the much larger whole-cell pools. To investigate the origins of these pools, we analyzed HeLa cell mitochondria for ribonucleotide reductase activity. Three findings suggest specific association of a reductase with mitochondria: (1) enzyme activity in extracts of washed mitochondria, (2) stimulation of that activity by dATP at levels inhibitory to the major cellular activity, and (3) association of immunoreactive material with washed and fractionated mitochondria.