Intracellular proteolytic activity of the haloalkaliphilic archaeon Natronococcus occultus. Effect of starvation.

Intracellular proteolytic activity was detected in the haloalkaliphilic archaeon Natronococcus occultus during the stationary phase of cultures grown in complete medium and during carbon and nitrogen starvation. Puromycin prevented the occurrence of proteolytic activity in starved cells, suggesting that de novo synthesis of proteolytic enzymes might be required for protein degradation during starvation. Intracellular proteolytic activity degraded casein and gelatin. It had a temperature optimum of 60 degree centigrade in 2 M NaCl and depended on high salt concentration (NaCl or KCl) for activity and stability. Gelatin zymography of cell extracts from stationary phase or starved cells showed a complex pattern of proteolytic bands ranging from ∼ 20 to 120 kDa. All these proteolytic bands were inhibited by PMSF1) and chymostatin. However, they showed differences in stability to temperature and salt concentration.