What is the minimum amount of detergent needed for effective solubilization if the CMC is 5 mM?
Solubilization efficiency depends on detergent self-assembly thermodynamics above critical micelle concentration. Below CMC monomers dissolve individually with limited bilayer insertion causing minor perturbation without micelle formation. Above CMC cooperative aggregation produces spherical micelles of thirty to hundred monomers with hydrophobic core shielded and hydrophilic exterior, light scattering increases sharply and free monomer concentration remains near CMC. Micelles provide hydrophobic compartments that encapsulate lipids and transmembrane segments into water-soluble mixed micelles preventing aggregation while annular lipids may be retained when mild detergents used. CMC depends on tail length longer lowers CMC, headgroup ionic character, ionic strength and temperature. Effective extraction therefore requires concentration at or slightly above CMC providing micellar reservoir; typically one to two times CMC optimal, higher ratios risk delipidation and inactivation. For detergent with five millimolar CMC, six millimolar represents minimal supra-CMC condition allowing micelle formation and partitioning essential for purification of receptors and transporters while preserving activity.
Ref: Rosen and DeLisi, Detergent Properties and CMC in Membrane Protein Solubilization, Methods Enzymol.