Circular dichroism and fluorescence of polyethylene glycol-subtilisin in organic solvents.

Subtilisin Carlsberg has been made soluble in organic solvents such as dioxane and acetonitrile by covalent linking to polyethylene glycol. Far-ultraviolet circular dichroism and intrinsic protein fluorescence have shown that subtilisin dissolved in dioxane, in which the enzyme is active and highly stable, maintains the native secondary structure as well as the native microenvironment for tyrosyl residues. In acetonitrile subtilisin undergoes conformational changes that cause enzyme inactivation and precipitation.