This study examined how sodium chloride affects the activity and production of extracellular nuclease in Staphylococcus aureus. Researchers found that adding 1% NaCl enhanced nuclease activity approximately fourfold in enzymatic assays. The optimal conditions for enzyme activity varied with salt concentration: higher NaCl required increased calcium ion concentration and lower pH. Kinetic analysis revealed that NaCl affected the enzyme's maximum velocity (Vmax) but not its substrate affinity (Km). Other monovalent cations (KCl, CsCl, LiCl) showed similar stimulatory effects. In culture experiments, adding 3% NaCl to growing S. aureus cultures increased nuclease production roughly fivefold and prolonged the exponential growth phase. The stimulatory effect appeared unrelated to protein synthesis inhibition, suggesting instead that NaCl may facilitate membrane transport of the enzyme or permeation of an inducer molecule. These findings indicate that monovalent cations influence both the catalytic properties and biosynthesis of staphylococcal nuclease, contrary to previous reports suggesting salt had no effect on this enzyme.

Key findings

• Sodium chloride and other monovalent cations (KCl, CsCl, LiCl) enhanced staphylococcal exonuclease activity approximately fourfold at optimal concentrations around 1%
• The optimal pH and calcium ion concentration for nuclease activity shifted with increasing NaCl concentration, with higher salt requiring lower pH and higher Ca2+ levels
• NaCl affected enzyme kinetics by increasing Vmax but not altering Km, indicating effects on catalytic efficiency rather than substrate binding affinity
• Addition of 3% NaCl to culture media increased nuclease production fivefold compared to salt-free medium and prolonged exponential growth phase
• The monovalent cation effect on nuclease production appears independent of transcriptional or translational inhibition, possibly involving membrane transport mechanisms