Hyperactivation of serine proteases by the Hofmeister effect

alpha-Chymotrypsin (CHT) is a serine protease that hydrolyzes peptide bonds at the carboxyl end of hydrophobic amino acids. It has been shown that the enzyme activity of CHT increases one order of magnitude in the presence of some types of amine compounds and inorganic ions. Here we show that hyperactivation occurs for several kinds of serine proteases in the presence of a kosmotrope. Among the eight model enzymes, the catalytic activities of four serine protease increased 1.3-30-fold by the addition of 1.5 M sodium sulfate. Enzyme kinetics and circular dichroism analyses revealed that the hyperactivation is caused by both increased k(cat) and decreased K-M, which reflect stabilization of the active form of the enzyme and the affinity between the enzyme and hydrophobic substrate, respectively. These findings demonstrate the effectiveness of this simple method for enzyme activation without cost and contribute to our fundamental understanding of enzyme activity in solution.