Hofmeister effects in enzymatic activity:: Weak and strong electrolyte influences on the activity of Candida rugosa lipase

The effects of weak and strong electrolytes on the enzymatic activity of Candida rugosa lipase are explored. Weak electrolytes, used as buffers, set the pH, while strong electrolytes regulate the ionic strength. The interplay between pH and ionic strength has been assumed to be the determinant of enzymatic activity. In experiments that probe activities by varying these parameters, there has been little attention focused on the role of specific electrolyte effects. Here we show that both buffers and the choice of background electrolyte ion strongly affect the enzymatic activity of Candida rugosa lipase. The effects here shown are dramatic at high salt concentration; indeed, a 2 M concentration of NaSCN is able to fully inactivate the lipase. By contrast, Na2SO4 acts generally as an activator, whereas NaCl shows a quasi-neutral behavior. Such specific ion effects are well-known and are classified among the Hofmeister effects. However, there has been little awareness of them, or of their potential for optimization of activities in the enzyme community. Rather than the effects per se, the focus here is on their origin. New insights into mechanism are proposed.