Physical Parameters of Solubilized Membrane Proteins

From solubilized membrane proteins you can— without major equipment—determine MW, Stokes radius, sedimentation coefficient, proportion of bound detergent and phospholipid, isoelectric point, and the apparent frictional coefficient. Knowledge of Stokes radius, MW, and isoelectric point comes in handy during planning of a purification or drafting of a detection assay (the other measures are good for the library). 

A gel filtration (e.g., to Sepharose 6B or CL 6B) yields the Stokes radius of the protein-detergent-phospholipid complex, provided you also run marker proteins of known Stokes radius (e.g., P-galactosidase 6.9 nm apoferritin 6.1 nm catalase 5.2 nm BSA 3.55 nm). The method does not determine the protein MW (because of detergent and phospholipid in the complex). 

Chromatofocusing is suited for determining the isoelectric point of membrane proteins. It also provides substantial enrichment. For chromatofocusing, the protein must also be stable with low ion strength (salt interferes with focusing), and you may not use any ionic detergents such as deoxycholate, cholate, or SDS. 

Clarke, S. (1975). The Size and Detergent Binding of Membrane Proteins, /. Biol. Chem. 250 5459-5469. 

(1977). Hydrodynamic Properties of the P-adrenetgic Receptor and Adenylate Cyclase from 

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