Thermal stability and enzymatic activity of RNase A in the presence of cationic gemini surfactants

The thermal stability and enzymatic activity of bovine pancreatic ribonuclease A (RNase A) have been investigated in the presence of a homologous series of cationic gemini surfactants (alkanediyl-α,ω-bis(hydroxyethyl methyl hexadecyl ammonium bromide)). UV, circular dichorism and fluorescence spectroscopies have been used for this study. The denaturation curves at various surfactant concentrations were analyzed on basis of a two-transition model to obtain values of Tm (temperature at the midpoint of denaturation) and ΔHm (enthalpy change at Tm) of each transition. The main conclusion of this study is that these cationic gemini surfactants slightly activate and stabilize RNase A below their critical micelle concentrations at pH 5.0. The cationic gemini surfactant with the shorter spacer interacts more efficiently with RNase A than those with longer spacers.

► Thermal denaturation of RNase A in the presence of cationic gemini surfactants is two distinct transitions (native ↔ intermediate ↔ denaturated).
► Cationic gemini surfactants slightly activate and stabilize RNase A sub-CMC.
► Stability of RNase A solution increases with increasing of spacer length from 4 to 6.