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#detergent

4 public questions tagged with this topic.

Lipid Link Protein

What happens when detergent concentration is below the CMC?

Understanding CMC highlights phase behavior of amphiphiles. At subsaturation detergent monomers exist dissolved in aqueous phase hydration shell disordered, partial insertion into outer leaflet may increase permeability but leaves bilayer structure largely intact. When monomer concentration reaches thermodynamic threshold where entropic cost of ordering water around hydrophobic tails outweighs micellization free energy, spontaneous aggregation into micelles occurs with hydrocarbon tails sequestered interior and polar heads facing water forming spherical or ellipsoidal particles thirty to fifty angstroms diameter. Below this point no micelles detected by dye solubilization, surface tension or NMR; membranes not disrupted into mixed micelles, so integral proteins remain embedded and organelle barriers persist demonstrated by retention of luminal markers. This intentional sub-CMC usage allows delivery of hydrophobic drugs or limited permeabilization. For complete lysis and purification supra-CMC concentrations mandatory providing sufficient micelles to sequester phospholipids and proteins into soluble particles preventing aggregation and inactivation during biochemical isolation. Experimental determination of CMC using light scattering fluorescent probes ANS or N-phenyl naphthylamine tracks abrupt intensity increase indicating micellization.

Ref: le Maire et al., Interaction of Membrane Proteins and Detergents, Biochim Biophys Acta 2000.

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Lipid Link Protein

Which of the following is a membrane-permeable detergent?

Detergent physicochemical properties determine permeabilization without denaturation. Triton X-100 tert-octylphenyl polyethoxyethanol consists of hydrophobic tert-octylphenol moiety and hydrophilic polyoxyethylene chain averaging nine to ten units, conferring CMC near zero point two four millimolar, aggregation number about one hundred to one fifty and micellar weight around ninety kilodalton. It partitions efficiently into phospholipid bilayers increasing permeability to macromolecules like antibodies and substrates, forming mixed micelles that solubilize lipids while protein-protein electrostatic contacts and hydrophobic core packing of soluble domains remain undisturbed because headgroup uncharged does not bind backbone cooperatively. SDS anionic twelve-carbon sulfate displays low CMC but strong cooperative binding unfolding helices and beta sheets into rodlike micelles. Sodium deoxycholate bile salt anionic steroid forms smaller micelles relatively harsh. For gentle permeabilization preserving enzyme activity, antigenicity and protein complexes, Triton X-100 remains laboratory standard, explaining identification as membrane-permeable non-denaturing detergent distinct from ionic denaturants used for SDS-PAGE. Quantitative assessment of protein activity after extraction confirms retention of ligand binding and catalytic turnover essential for biochemical characterization.

Ref: Seddon et al., Methods Mol Biol, Membrane Protein Solubilization and Detergent Properties.

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Lipid Link Protein

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.

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