Ionizing Radiation-Induced Release of a Cell Surface Nuclease from Micrococcus radiodurans

Micrococcus radiodurans possesses an exonuclease (orthophosphoric diester phosphohydrolase EC 3.1.4.1) bound to its cell surface. Exposure to ionizing radiation causes release of this activity into the surrounding medium; less than 10% remains cell associated after 400 krad dose (sublethal). This enzyme is not normally excreted. The extent of release is a function of total ionizing radiation dose only, and is independent of dose rate or temperature. This enzyme is not involved in the postirradiation DNA degradation that accompanies repair in this organism. A 5′-nucleotidase also located in the cell envelope is not released under these conditions. Since only a small amount of the total cell protein is released, an initial enzyme purification of about 150-fold could be achieved relative to crude extracts.