Kinetics of Detergent-Induced Activation and Inhibition of a Minimal Lipase

Detergents are commonly applied in lipase assays to solubilize sparingly soluble model substrates. However, detergents affect lipases as well as substrates in multiple ways. The effect of detergents on lipase activity is commonly attributed to conformational changes in the lid region. This study deals with the effect of the nonionic detergent, poly(ethylene glycol) dodecyl ether, on a lipase that does not contain a lid sequence, lipase A from Bacillus subtilis (BSLA). We show that BSLA activity depends strongly on the detergent concentration and the dependency profile changes with pH. The interaction of BSLA with detergent monomers and micelles is studied using fluorescence correlation spectroscopy, time-resolved anisotropy decay, and temperature-induced unfolding. Detergent-dependent hydrolysis kinetics of two different substrates at two pH values are fitted with a microkinetic model. This analysis shows that the mechanism of interfacial lipase catalysis is strongly affected by the detergent. It reveals an activation mechanism by monomeric detergent that does not result from structural changes of the lipase. Instead, we propose that interfacial diffusion of the lipase is enhanced by detergent binding.