EFFECT OF SALTS ON THE ACTIVITY OF NITRATE REDUCTASE FROM THE PHOTOSYNTHETIC BACTERIUM RHODOBACTER-SPHAEROIDES SW

The effect of different salts on the nitrate reductase (NR) activity o f Rhodobacter sphaeroides SW was studied. An increase of the activity in the presence of monovalent cations was observed (90, 80 and 77% wit h Na+, K+ and NH4+, respectively), whereas divalent cations inhibited the enzyme activity (30 acid 85% with Ca2+ and Mg2+). Both activation or inhibition of the NR activity were reversible. These results could be explained by the interaction of cations with negatively charged ami no acids. On the other hand, several anions were also effective in sti mulating NR activity (Cl- > NO3- > Br- > I- > SCN-), suggesting that t he degree of hydration of the enzyme molecule might influence its acti vity. Finally, the effect of salts on the NR activity of R. sphaeroide s SW can heattributed to both electrostatic and hydrophobic interactio ns.